Origin of hydrodynamic turbulence in rotating shear flows is investigated. The particular emphasis is the flows whose angular velocity decreases but specific angular momentum increases with increasing radial coordinate. Such flows are Rayleigh stable, but must be turbulent in order to explain observed data. Such a mismatch between the linear theory and observations/experiments is more severe when any hydromagnetic/magnetohydrodynamic instability and then the corresponding turbulence therein is ruled out. The present work explores the effect of stochastic noise on such hydrodynamic flows. We essentially concentrate on a small section of such a flow which is nothing but a plane shear flow supplemented by the Coriolis effect. This also mimics a small section of an astrophysical accretion disk. It is found that such stochastically driven flows exhibit large temporal and spatial correlations of perturbation velocities, and hence large energy dissipations of perturbation, which presumably generate instability. A range of angular velocity (\Omega) profiles of background flow, starting from that of constant specific angular momentum (\lambda = \Omega r^2 ; r being the radial coordinate) to that of constant circular velocity (v_\phi = \Omega r), is explored. However, all the background angular velocities exhibit identical growth and roughness exponents of perturbations, revealing a unique universality class for the stochastically forced hydrodynamics of rotating shear flows. This work, to the best of our knowledge, is the first attempt to understand origin of instability and turbulence in the three-dimensional Rayleigh stable rotating shear flows by introducing additive noise to the underlying linearized governing equations. This has important implications to resolve the turbulence problem in astrophysical hydrodynamic flows such as accretion disks.
We study the basic properties of accretion flows onto binary supermassive black holes, including the cases in which a circumbinary disk is misaligned with the binary orbital plane, by means of three-dimensional Smoothed Particle Hydrodynamics simulations. We find that a circular binary system with a misaligned circumbinary disk normally produces a double peaked mass-accretion-rate variation per binary orbit. This is because each black hole passes across the circumbinary disk plane and captures gas twice in one orbital period. Even in misaligned systems, however, a single peaked mass-accretion-rate variation per binary orbit is produced, if the orbital eccentricity is moderately large (e\lesssim0.3). The number of peaks in mass accretion rates can be understood simply in terms of the orbital phase dependence of the distance between each binary black hole and its closest inner edge of the circumbinary disk. In the cases of eccentric binary black holes having different masses, the less massive black hole can get closer to the circumbinary disk than the massive one, thus tidally splitting gas from its inner edge, but the created gas flows are comparably captured by both black holes with a short time delay. As a consequence, the combined light curve shows periodic occurrence of double-peaked flares with a short interval. This may account for the observed light variations of OJ287.
We place general constraints on the luminosity and mass of hot X-ray emitting gas residing in extended "hot halos" around nearby massive galaxies. We examine stacked images of 2165 galaxies from the 2MASS Very Isolated Galaxy Catalog (2MVIG), as well as subsets of this sample based on galaxy morphology and K-band luminosity. We detect X-ray emission at high confidence (ranging up to nearly 10\sigma) for each subsample of galaxies. The average L_X within 50 kpc is 1.0\pm0.1 (statistical) \pm0.2 (systematic) x10^40 erg/s, although the early-type galaxies are more than twice as luminous as the late-type galaxies. Using a spatial analysis, we also find evidence for extended emission around five out of seven subsamples (the full sample, the luminous galaxies, early-type galaxies, luminous late-type galaxies, and luminous early-type galaxies) at 92.7%, 99.3%, 89.3%, 98.7%, and 92.1% confidence, respectively. Several additional lines of evidence also support this conclusion and suggest that about 1/2 of the total emission is extended, and about 1/3 of the extended emission comes from hot gas. For the sample of luminous galaxies, which has the strongest evidence for extended emission, the average hot gas mass is 4x10^9 Msun within 50 kpc and the implied accretion rate is 0.4 Msun/yr.
Given the extreme precision attainable with the Kepler Space Telescope, the mitigation of instrumental artefacts is very important. In an earlier paper (Murphy 2012), the characteristics of Kepler data were discussed in light of their effect on asteroseismology. We continue this discussion now that data processed with the new PDC-MAP pipeline are publicly available; users should use the latest data reductions available at the Mikulski Archive for Space Telescopes (MAST), not just for PDC, but also for improvements in the attached meta-data. We discuss the injection of noise in the frequency range 0-24 c/d (up to ~277 {\mu}Hz) by the PDC-LS pipeline into ~15 per cent of light-curves.
We present the BOSS Lyman-alpha (Lya) Forest Sample from SDSS Data Release 9, comprising 54,468 quasar spectra with zqso > 2.15 suitable for Lya forest analysis. This data set probes the intergalactic medium with absorption redshifts 2.0 < z_alpha < 5.7 over an area of 3275 square degrees, and encompasses an approximate comoving volume of 20 h^-3 Gpc^3. With each spectrum, we have included several products designed to aid in Lya forest analysis: improved sky masks that flag pixels where data may be unreliable, corrections for known biases in the pipeline estimated noise, masks for the cores of damped Lya systems and corrections for their wings, and estimates of the unabsorbed continua so that the observed flux can be converted to a fractional transmission. The continua are derived using a principal component fit to the quasar spectrum redwards of restframe Lya (lambda > 1216 Ang), extrapolated into the forest region and normalized by a linear function to fit the expected evolution of the Lya forest mean-flux. The estimated continuum errors are ~5% rms. We also discuss possible systematics arising from uncertain spectrophotometry and artifacts in the flux calibration; global corrections for the latter are provided. Our sample provides a convenient starting point for users to analyze clustering in BOSS Lya forest data, and it provides a fiducial data set that can be used to compare results from different analyses of baryon acoustic oscillations in the Lya forest. The full data set is available from the SDSS-III DR9 web site.
The first calibrated broadband BVI time-series photometry is presented for the variable stars in NGC 2808, with observations spanning a range of twenty-eight years. We have also redetermined the variability types and periods for the variable stars identified previously by Corwin et al, revising the number of probable fundamental-mode RR Lyrae variables (RR0) to 11 and the number of first-overtone variables (RR1) to five. Our observations were insufficient to discern the nature of the previously identified RR1 star, V24, and the tentatively identified RR1 star, V13. These two variables are \sim0.8 mag brighter than the RR Lyrae variables, appear to have somewhat erratic period and/or luminosity changes, and lie inside the RR Lyrae instability strip. Curiously, all but one of the RR Lyrae stars studied in this relatively metal-rich cluster exhibit the Blazhko phenomenon, an effect thought to occur with higher frequency in metal-poor environments. The mean periods of the RR0 and RR1 variables are <P>_RR0=0.56 pm 0.01 d and <P>_RR1=0.30 pm 0.02 d, respectively, supporting an Oosterhoff I classification of the cluster. On the other hand, the number ratio of RR1- to RR0-type variables is high, though not unprecedented, for an Oosterhoff I cluster. The RR Lyrae variables have no period shifts at a given amplitude as compared to the M3 variables, making it unlikely that these variables are He-enhanced. Using the recent recalibration of the RR Lyrae luminosity scale by Catelan & Cortes, a mean distance modulus of (m-M)_V= 15.57 pm 0.13 mag for NGC 2808 is obtained, in good agreement with that determined here from its type II Cepheid and SX Phoenicis population. Our data have also allowed the discovery of two new candidate SX Phoenicis stars and an eclipsing binary in the blue straggler region of the NGC 2808 color-magnitude diagram.
We present 1.3 millimeter ALMA Cycle 0 observations of the edge-on debris disk around the nearby, ~10 Myr-old, M-type star AU Mic. These observations obtain 0.6 arcsec (6 AU) resolution and reveal two distinct emission components: (1) the previously known dust belt that extends to a radius of 40 AU, and (2) a newly recognized central peak that remains unresolved. The cold dust belt of mass about 1 lunar mass is resolved in the radial direction with a rising emission profile that peaks sharply at the location of the outer edge of the "birth ring" of planetesimals hypothesized to explain the midplane scattered light gradients. No significant asymmetries are discerned in the structure or position of this dust belt. The central peak identified in the ALMA image is ~6 times brighter than the stellar photosphere, which indicates an additional emission process in the inner regions of the system. Emission from a stellar corona or activity may contribute, but the observations show no signs of temporal variations characteristic of radio-wave flares. We suggest that this central component may be dominated by dust emission from an inner planetesimal belt of mass about 0.01 lunar mass, consistent with a lack of emission shortward of 25 microns and a location <3 AU from the star. Future millimeter observations can test this assertion, as an inner dust belt should be readily separated from the central star at higher angular resolution.
The appearance of the B[e] phenomenon in evolved massive stars such as B[e] supergiants is still a mystery. While these stars are generally found to have disks that are cool and dense enough for efficient molecule and dust condensation, the origin of the disk material is still unclear. We aim at studying the kinematics and origin of the disk in the eccentric binary system GG Car, whose primary component is proposed to be a B[e] supergiant. Based on medium- and high-resolution near-infrared spectra we analyzed the CO-band emission detected from GG Car. The complete CO-band structure delivers information on the density and temperature of the emitting region, and the detectable 13CO bands allow us to constrain the evolutionary phase. In addition, the kinematics of the CO gas can be extracted from the shape of the first 12CO band head. We find that the CO gas is located in a ring surrounding the eccentric binary system, and its kinematics agrees with Keplerian rotation with a velocity, projected to the line of sight, of (80\pm 1) km/s. The CO ring has a column density of (5\pm 3)x10^21 cm^-2 and a temperature of 3200\pm 500 K. In addition, the material is chemically enriched in 13CO, which agrees with the primary component being slightly evolved off the main sequence. We discuss two possible scenarios for the origin of the circumbinary disk: (i) non-conservative Roche lobe overflow, and (ii) the possibility that the progenitor of the primary component could have been a classical Be star. Neither can be firmly excluded, but for Roche lobe overflow to occur, a combination of stellar and orbital parameter extremawould be required.
With the aim of assessing the effects of bars on active galactic nuclei (AGN), we present an analysis of host characteristics and nuclear activity of AGN galaxies with and without bars selected from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7). By visual inspection of SDSS images we classified the hosts of face-on AGN spiral galaxies brighter than g < 16.5 into barred or unbarred. With the purpose of providing an appropriate quantification of the effects of bars, we also constructed a suitable control sample of unbarred AGN galaxies with similar redshift, magnitude, morphology, bulge sizes and local environment distributions. We find that the bar fraction, with respect to the full sample of spiral face-on AGN host galaxies, is 28.5%, in good agreement with previous works. Barred AGN host galaxies show an excess of young stellar populations dominated by red u-r and g-r colors, with respect to the control sample, suggesting that bars produce an important effect on galaxy properties of AGN hosts. Regarding the nuclear activity distribution, we find that barred AGN galaxies show a shift toward higher Lum[OIII] values with respect to AGN without bars. In addition, we also find that this trend is more significant in less massive, younger stellar population and bluer AGN host galaxies. We found that the fraction of powerful AGN increase towards more massive hosts with bluer colors and younger stellar populations residing in denser environments. However, barred host AGN systematically show a higher fraction of powerful active nuclei galaxies with respect to the control sample. We also explored the accretion rate onto the central black holes finding that barred AGN show an excess of objects with high accretion rate values with respect to unbarred AGN galaxies.
Star formation is self-regulated by its feedback that drives turbulence and heats the gas. In equilibrium, the star formation rate (SFR) should be directly related to the total (thermal plus turbulent) midplane pressure and hence the total weight of the diffuse gas if energy balance and vertical dynamical equilibrium hold simultaneously. To investigate this quantitatively, we utilize numerical hydrodynamic simulations focused on outer-disk regions where diffuse atomic gas dominates. By analyzing gas properties at saturation, we obtain relationships between the turbulence driving and dissipation rates, heating and cooling rates, the total midplane pressure and the total weight of gas, and the SFR and the total midplane pressure. We find a nearly linear relationship between the SFR and the midplane pressure consistent with the theoretical prediction.
The existence of intermediate-mass ($\sim 10^3 M_\odot$) black holes in the center of globular clusters has been suggested by different observations. Extended, central X-ray sources observed in NGC 6388 and in G1 in M31 could be interpreted as being powered by the accretion of matter onto such objects. In this work we explore a scenario in which the black hole accretes from the cluster interstellar medium, which is generated by the mass loss of the red giants in the cluster. We estimate the accretion rate onto the black hole and compare it to the values obtained via the traditional Bondi-Hoyle model. Our results show that the accretion rate is no longer solely defined by the black hole mass and the ambient parameters but also by the host cluster itself. Furthermore, we find that the more massive globular clusters with large stellar velocity dispersion are the best candidates in which accretion onto IMBHs could be detected.
We used the Pixelised Wavelet Filtering (PWF) method to compute narrow-band power maps of SDO/AIA imaging datasets in the 1700 \AA{}, 1600 \AA{} and 304 \AA{} bandpasses that correspond to different heights. The cut-off frequency was defined as contours where the spectral power droped to the median level. It was measured as a function of the spatial location. We inferred the magnetic field inclination according to the MAG wave theory in the low-$\beta$ limit and compared it with the potential field extrapolation.{We analysed intensity oscillations in a symmetric sunspot AR11131(08 Dec 2010) and an asymmetric sunspot AR11330 (27 Oct 2011). We reconstructed the magnetic field inclination in the radial direction for the symmetric sunspot and in both radial and azimuthal directions for the asymmetric sunspot. We observed 3D variation of the main oscillation periods in sunspots. We found that shorter-period oscillations were mostly constrained in sunspot umbrae, while longer-period oscillations formed an annular shape enclosing the umbra. Longer periods are found to be distributed further away from the sunspot centre. Our results indicate that 3-min oscillation are generated in the chromosphere, possibly by the acoustic resonator model, while 5-min and longer-period oscillations seemed to originate in a level under the photosphere. The reconstructed field inclinations gives the values of the field inclination that are systematically larger than the values obtained by the potential field extrapolation. The inclined magnetic field line can account for 60-80% of cut-offfrequency lowering only.
We present the results of high spatial resolution observations at 1.1 mm waveband, with the Submillimeter Array (SMA), towards the protocluster G10.6-0.4. The 1.1 mm continuum emission reveals seven dense cores, in which infall motions are all detected with the red-shifted absorption dips in HCN (3--2) line. This is the first time that infall is seen towards multiple sources in a protocluster. The dense core located in the center has the largest mass and mass infall rate and dominates the gas accretion of the protocluster, while the off-center cores have much smaller masses and mass infall rates, which favors the "competitive accretion" model. We also identified four infrared point sources in this region, which are most likely Class 0/I protostars. Two jet-like structures are also identified from Spitzer/IRAC image.
Pulsed gamma-ray emission from millisecond pulsars (MSPs) has been detected by the sensitive Fermi, which sheds light on studies of the emission region and mechanism. In particular, the specific patterns of radio and gamma-ray emission from PSR J0101-6422 challenge the popular pulsar models, e.g. outer gap and two-pole caustic (TPC) models. Using the three dimension (3D) annular gap model, we have jointly simulated radio and gamma-ray light curves for three representative MSPs (PSR J0034-0534, PSR J0101-6422 and PSR J0437-4715) with distinct radio phase lags and present the best simulated results for these MSPs, particularly for PSR J0101-6422 with complex radio and gamma-ray pulse profiles and for PSR J0437-4715 with a radio interpulse. It is found that both the gamma-ray and radio emission originate from the annular gap region located in only one magnetic pole, and the radio emission region is not primarily lower than the gamma-ray region in most cases. In addition, the annular gap model with a small magnetic inclination angle instead of "orthogonal rotator" can account for MSPs' radio interpulse with a large phase separation from the main pulse. The annular gap model is a self-consistent model not only for young pulsars but also MSPs, and multi-wavelength light curves can be fundamentally explained by this model.
We discover that the mass of dark matter particles mDM is imprinted in phase-correlations of the cosmic density field more significantly than in the 2-point correlation. In particular, phase-correlations trace mDM out to scales about five times larger than the 2-point correlation. This result relies on a new estimator l(r) of pure phase-information in Fourier space, which can be interpreted as a parameter-free and scale-invariant tracer of filament-like structure. Based on simulated density fields we show how mDM can, in principle, be measured using l(r), given a suitably reconstructed density field.
There exists a special class of X-ray pulsars that exhibit very slow pulsation of $P_{\rm spin}>1000$ s in the high mass X-ray binaries (HMXBs). We have studied the temporal and spectral properties of these superslow pulsation neutron star binaries in hard X-ray bands with INTEGRAL observations. Long-term monitoring observations find spin period evolution of two sources: spin-down trend for 4U 2206+54 ($P_{\rm spin}\sim 5560$ s with $\dot{P}_{\rm spin}\sim 4.9\times 10^{-7}$ s s$^{-1}$) and long-term spin-up trend for 2S 0114+65 ($P_{\rm spin}\sim 9600$ s with $\dot{P}_{\rm spin}\sim -1\times 10^{-6}$ s s$^{-1}$) in the last 20 years. A Be X-ray transient, SXP 1062 ($P_{\rm spin}\sim 1062$ s), also showed a fast spin-down rate of $\dot{P}_{\rm spin}\sim 3\times 10^{-6}$ s s$^{-1}$ during an outburst. These superslow pulsation neutron stars cannot be produced in the standard X-ray binary evolution model unless the neutron star has a much stronger surface magnetic field ($B>10^{14}$ G). The physical origin of the superslow spin period is still unclear. The possible origin and evolution channels of the superslow pulsation X-ray pulsars are discussed. Superslow pulsation X-ray pulsars could be younger X-ray binary systems, still in the fast evolution phase preceding the final equilibrium state. Alternatively, they could be a new class of neutron star system $-$ accreting magnetars.
We propose the new scenario for X-ray outbursts in Be/X-ray binaries that normal and giant outbursts are respectively caused by radiatively inefficient accretion flows (RIAFs) and Bondi-Hoyle-Lyttleton (BHL) accretion of the material transferred from the outermost part of a Be disk misaligned with the binary orbital plane. Based on simulated mass-transfer rates from misaligned Be disks, together with simplified accretion flow models, we show that mass-accretion rates estimated from the luminosity of the normal X-ray outbursts are consistent with those obtained with advection-dominated accretion flows, not with the standard, radiative-cooling dominated, accretion. Our RIAF scenario for normal X-ray outbursts resolves problems that have challenged the standard disk picture for these outbursts. When a misaligned Be disk crosses the orbit of the neutron star, e.g., by warping, the neutron star can capture a large amount of mass via BHL-type accretion during the disk transit event. We numerically show that such a process can reproduce the X-ray luminosity of giant X-ray outbursts. In the case of very high Be disk density, the accretion flow associated with the disk transit becomes supercritical, giving rise to the luminosity higher than the Eddington luminosity.
We present a study of the star formation histories of the Lupus I, III, and IV clouds using the Herschel 70-500 micron maps obtained by the Herschel Gould Belt Survey Key Project. By combining the new Herschel data with the existing Spitzer catalog we obtained an unprecedented census of prestellar sources and young stellar objects in the Lupus clouds, which allowed us to study the overall star formation rate (SFR) and efficiency (SFE). The high SFE of Lupus III, its decreasing SFR, and its large number of pre-main sequence stars with respect to proto- and prestellar sources, suggest that Lupus III is the most evolved cloud, and after having experienced a major star formation event in the past, is now approaching the end of its current star-forming cycle. Lupus I is currently undergoing a large star formation event, apparent by the increasing SFR, the large number of prestellar objects with respect to more evolved objects, and the high percentage of material at high extinction (e.g., above A_V=8 mag). Also Lupus IV has an increasing SFR; however, the relative number of prestellar sources is much lower, suggesting that its star formation has not yet reached its peak.
We summarize our ground-based program of spectroscopic and photometric observations of the asteroseismic targets of the Kepler space telescope. We have already determined atmospheric parameters, projected velocity of rotation, and radial velocity of 62 Kepler asteroseismic targets and 33 other stars in the Kepler field of view. We discovered six single-lined and two double-lined spectroscopic binaries, we determined the interstellar reddening for 29 stars in the Kepler field of view, and discovered three delta Sct, two gamma Dor and 14 other variable stars in the field of NGC 6866.
We investigate accreting disk systems with polytropic gas in Keplerian motion. Numerical data and partial analytic results show that the self-gravitation of the disk speeds up its rotation -- its rotational frequency is larger than that given by the well known strictly Keplerian formula that takes into account the central mass only. Thus determination of central mass in systems with massive disks requires great care -- the strictly Keplerian formula yields only an upper bound. The effect of self-gravity depends on geometric aspects of disk configurations. Disk systems with a small (circa $10^{-4}$) ratio of the innermost radius to the outermost disk radius have the central mass close to the upper limit, but if this ratio is of the order of unity then the central mass can be smaller by many orders of magnitude from this bound.
During a solar magnetic field reversal the magnetic dipole moment does not vanish, but migrates between poles, in contradiction to the predictions of mean-field dynamo theory. We try to explain this as a consequence of magnetic fluctuations. We exploit the statistics of fluctuations to estimate observable signatures. Simple statistical estimates, taken with results from mean-field dynamo theory, suggest that a non-zero dipole moment may persist through a global field reversal. Fluctuations in the solar magnetic field may play a key role in explaining reversals of the dipolar component of the field.
We present long-slit integrated spectroscopy of 238 late-type galaxies belonging to the Herschel Reference Survey, a volume limited sample representative of the nearby universe. This sample has a unique legacy value since ideally defined for any statistical study of the multifrequency properties of galaxies spanning a large range in morphological type and luminosity. The spectroscopic observations cover the spectral range 3600-6900 A at a resolution R ~ 1000 and are thus suitable for separating the underlying absorption from the emission of the Hbeta line as well as the two [NII] lines from the Halpha emission. We measure the fluxes and the equivalent widths of the strongest emission lines ([OII], Hbeta, [OIII], [NII], Halpha, and [SII]). The data are used to study the distribution of the equivalent width of all the emission lines, of the Balmer decrement C(Hbeta) and of the observed underlying Balmer absorption under Hbeta in this sample. Combining these new spectroscopic data with those available at other frequencies, we also study the dependence of C(Hbeta) and E.W.Hbeta_{abs} on morphological type, stellar mass and stellar surface density, star formation rate, birthrate parameter and metallicity in galaxies belonging to different environments (fields vs. Virgo). The distribution of the equivalent width of all the emission lines, of C(Hbeta) and E.W.Hbeta_{abs} are systematically different in cluster and field galaxies. The Balmer decrement increases with stellar mass, stellar surface density, metallicity and star formation rate of the observed galaxies, while it is unexpectedly almost independent from the column density of the atomic and molecular gas. The dependence of C(Hbeta) on stellar mass is steeper than that previously found in other works. The underlying Balmer absorption does not significantly change with any of these physical parameters.
We investigate claims of excess ellipticity of hot and cold spots in the WMAP data (Gurzadyan et al. 2005, 2007). Using the cosmic microwave background data from 7 years of observations by the WMAP satellite, we find, contrary to previous claims of a 10 sigma detection of excess ellipticity in the 3-year data, that the ellipticity of hot and cold spots are perfectly consistent with simulated CMB maps based on the concordance cosmology. We further test for excess obliquity and excess skewness/kurtosis of ellipticity and obliquity and find the WMAP7 data consistent with Gaussian simulated maps.
The current understanding of the spin evolution of young pulsars is reviewed through a compilation of braking index measurements. An immediate conclusion is that the spin evolution of all pulsars with a measured braking index is not purely caused by a constant magnetic dipole. The case of PSR J1734-3333 and its upward movement towards the magnetars is used as a guide to try to understand why pulsars evolve with n < 3. Evolution between different pulsar families, driven by the emergence of a hidden internal magnetic field, appears as one possible picture.
We present an analysis of the photometric variability of M dwarfs in the WFCAM Transit Survey. Although periodic lightcurve variability in low mass stars is generally dominated by photospheric star spot activity, M dwarf variability in the J band has not been as thoroughly investigated as at visible wavelengths. Spectral type estimates for a sample of over 200,000 objects are made using spectral type-colour relations, and over 9600 dwarfs (J<17) with spectral types later than K7 were found. The light curves of the late-type sample are searched for periodicity using a Lomb-Scargle periodogram analysis. A total of 68 periodic variable M dwarfs are found in the sample with periods ranging from 0.16 days to 90.33 days, with amplitudes in the range of ~0.009 to ~0.115 in the J band. We simulate active M dwarfs with a range of latitude-independent spot coverages and estimate a periodically variable fractions of 1-3 per cent for stars where spots cover more than 10 per cent of the star's surface. Our simulated spot distributions indicate that operating in the J band, where spot contrast ratios are minimised, enables variability in only the most active of stars to be detected. These findings affirm the benefits of using the $J$ band for planetary transit searches compared to visible bands. We also serendipitously find a \Delta J>0.2 mag flaring event from an M4V star in our sample.
We present photometric and spectroscopic analysis of AE For -- a detached eclipsing binary composed of two late K dwarfs. The masses of the components are found to be 0.6314 +- 0.0035 and 0.6197 +- 0.0034 Msun and the radii to be 0.67 +- 0.03 and 0.63$ +- 0.03 Rsun for primary and secondary component, respectively. Both components are significantly oversized compared to theoretical models, which we attribute to their high activity. They show Halpha, Hbeta, Hgamma, Ca H and Ca K lines in emission, and are heavily spotted, causing large variations of the light curve.
We have studied a sample of 296 faint (> 0.5 mJy) radio sources selected from
an area of the Tenth Cambridge (10C) survey at 15.7 GHz in the Lockman Hole. By
matching this catalogue to several lower frequency surveys (e.g. including a
deep GMRT survey at 610 MHz, a WSRT survey at 1.4 GHz, NVSS, FIRST and WENSS)
we have investigated the radio spectral properties of the sources in this
sample; all but 30 of the 10C sources are matched to one or more of these
surveys. We have found a significant increase in the proportion of flat
spectrum sources at flux densities below approximately 1 mJy - the median
spectral index between 15.7 GHz and 610 MHz changes from 0.75 for flux
densities greater than 1.5 mJy to 0.08 for flux densities less than 0.8 mJy.
This suggests that a population of faint, flat spectrum sources is emerging at
flux densities below 1 mJy.
The spectral index distribution of this sample of sources selected at 15.7
GHz is compared to those of two samples selected at 1.4 GHz from FIRST and
NVSS. We find that there is a significant flat spectrum population present in
the 10C sample which is missing from the samples selected at 1.4 GHz. The 10C
sample is compared to a sample of sources selected from the SKADS Simulated Sky
by Wilman et al. and we find that this simulation fails to reproduce the
observed spectral index distribution and significantly underpredicts the number
of sources in the faintest flux density bin. It is likely that the observed
faint, flat spectrum sources are a result of the cores of FRI sources becoming
dominant at high frequencies. These results highlight the importance of
studying this faint, high frequency population.
Research into hot subdwarf stars is progressing rapidly. We present recent important discoveries. First we review the knowledge about magnetic fields in hot subdwarfs and highlight the first detection of a highly-magnetic, helium-rich sdO star. We briefly summarize recent discoveries based on Kepler light curves and finally introduce the closest known sdB+WD binary discovered by the MUCHFUSS project and discuss its relevance as progenitor of a double-detonation type Ia supernova.
(Abridged) This paper explores the use of k-means clustering as a tool for automated unsupervised classification of massive stellar spectral catalogs. The classification criteria are defined by the data and the algorithm, with no prior physical framework. We work with a representative set of stellar spectra associated with the SDSS SEGUE and SEGUE-2 programs. We classify the original spectra as well as the spectra with the continuum removed. The second set only contains spectral lines, and it is less dependent on uncertainties of the flux calibration. The classification of the spectra with continuum renders 16 major classes. Roughly speaking, stars are split according to their colors, with enough finesse to distinguish dwarfs from giants of the same effective temperature, but with difficulties to separate stars with different metallicities. Overall, there is no one-to-one correspondence between the classes we derive and the MK types. The classification of spectra without continuum renders 13 classes, the color separation is not so sharp, but it distinguishes stars of the same effective temperature and different metallicities. Some classes thus obtained present a fairly small range of physical parameters (200 K in effective temperature, 0.25 dex in surface gravity, and 0.35 dex in metallicity), so that the classification can be used to estimate the main physical parameters of some stars at a minimum computational cost. We also analyze the outliers of the classification. Most of them turn out to be failures of the reduction pipeline, but there are also high redshift QSOs, multiple stellar systems, dust-reddened stars, galaxies, and, finally, odd spectra whose nature we have not decipher. The template spectra representative of the classes are publicly available (this ftp URL).
The depolarization asymmetry seen in double-lobed radio sources, referred to as the Laing-Garrington (L-G) effect where more rapid depolarization is seen in the lobe with no visible jet as the wavelength increases, can be explained either by internal differences between the two lobes, or by an external Faraday screen that lies in front of only the depolarized lobe. If the jet one-sidedness is due to relativistic beaming the depolarization asymmetry must be due to an intervening Faraday screen. If it is intrinsic the depolarization asymmetry must be related to internal differences in the lobes. We assume in this paper that the speed in the outer jet of several Fanaroff-Riley Class 1 (FRI) sources exhibiting the L-G effect is close to the 0.1c reported by several other investigators. For these sources we find that the jet one-sidedness cannot be explained by beaming and therefore must be intrinsic. In these FRI sources the L-G effect must be due to differences that originate inside the lobes themselves. Although it is not known if the flow in the outer jets of FRII sources also slows to this speed it is suggested that the explanation of the L-G effect is likely to be the same in both types. This argument is strengthened by the recent evidence that FRII galaxies have very large viewing angles, which in turn implies that the L-G model cannot work regardless of the jet velocity. It may therefore be too soon to completely rule out internal depolarization in the lobes as the true explanation for the L-G effect.
Recent numerical simulations of dynamo action resulting from rotating convection have revealed some serious problems in applying the standard picture of mean field electrodynamics at high values of the magnetic Reynolds number, and have thereby underlined the difficulties in large-scale magnetic field generation in this regime. Here we consider kinematic dynamo processes in a rotating convective layer of Boussinesq fluid with the additional influence of a large-scale horizontal velocity shear. Incorporating the shear flow enhances the dynamo growth rate and also leads to the generation of significant magnetic fields on large scales. By the technique of spectral filtering, we analyse the modes in the velocity that are principally responsible for dynamo action, and show that the magnetic field resulting from the full flow relies crucially on a range of scales in the velocity field. Filtering the flow to provide a true separation of scales between the shear and the convective flow also leads to dynamo action; however, the magnetic field in this case has a very different structure from that generated by the full velocity field. We also show that the nature of the dynamo action is broadly similar irrespective of whether the flow in the absence of shear can support dynamo action.
Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections
(ICMEs) where a magnetic flux rope is detected. Is the difference between MCs
and ICMEs without detected flux rope intrinsic or rather due to an
observational bias? As the spacecraft has no relationship with the MC
trajectory, the frequency distribution of MCs versus the spacecraft distance to
the MCs axis is expected to be approximately flat. However, Lepping and Wu
(2010) confirmed that it is a strongly decreasing function of the estimated
impact parameter. Is a flux rope more frequently undetected for larger impact
parameter? In order to answer the questions above, we explore the parameter
space of flux rope models, especially the aspect ratio, boundary shape, and
current distribution. The proposed models are analyzed as MCs by fitting a
circular linear force-free field to the magnetic field computed along simulated
crossings.
We find that the distribution of the twist within the flux rope, the
non-detection due to too low field rotation angle or magnitude are only weakly
affecting the expected frequency distribution of MCs versus impact parameter.
However, the estimated impact parameter is increasingly biased to lower values
as the flux-rope cross section is more elongated orthogonally to the crossing
trajectory. The observed distribution of MCs is a natural consequence of a
flux-rope cross section flattened in average by a factor 2 to 3 depending on
the magnetic twist profile. However, the faster MCs at 1 AU, with V>550 km/s,
present an almost uniform distribution of MCs vs. impact parameter, which is
consistent with round shaped flux ropes, in contrast with the slower ones. We
conclude that either most of the non-MC ICMEs are encountered outside their
flux rope or near the leg region, or they do not contain any.
We present new fast numerical simulations of cosmic microwave background and large scale structure in the case in which the cosmological dark matter is made entirely or partly of mirror matter. We consider scalar adiabatic primordial perturbations at linear scales in a flat Universe. The speed of the simulations allows us for the first time to use Markov Chain Monte Carlo analyses to constrain the mirror parameters. A Universe with pure mirror matter can fit very well the observations, equivalently to the case of an admixture with cold dark matter. In both cases, the analyses show a clear indication of the presence of a consistent amount of mirror dark matter, 0.05 < Omega_mirror h^2 < 0.12.
Apparent period variations detected in several eclipsing, close-compact binaries are frequently interpreted as being caused by circumbinary giant planets. This interpretation raises the question of the origin of the potential planets that must have either formed in the primordial circumbinary disk, together with the host binary star, and survived its evolution into a close-compact binary or formed in a post-common-envelope circumbinary disk that remained bound to the post-common-envelope binary (PCEB). Here we combine current knowledge of planet formation and the statistics of giant planets around primordial and evolved binary stars with the theory of close-compact binary star evolution aiming to derive new constraints on possible formation scenarios. We compiled a comprehensive list of observed eclipsing PCEBs, estimated the fraction of systems showing apparent period variations, reconstructed the evolutionary history of the PCEBs, and performed binary population models of PCEBs to characterize their main sequence binary progenitors. We reviewed the currently available constraints on the fraction of PCEB progenitors that host circumbinary giant planets. We find that the progenitors of PCEBs are very unlikely to be frequent hosts of giant planets (<~10 per cent), while the frequency of PCEBs with observed apparent period variations is very high (~90 per cent). The variations in eclipse timings measured in eclipsing PCEBs are probably not caused by first-generation planets that survived common-envelope evolution. The remaining options for explaining the observed period variations are second-generation planet formation or perhaps variations in the shape of a magnetically active secondary star. We suggest observational tests for both options.
We aim to identify and characterize secondary eclipses in the original light
curves of all published CoRoT planets using uniform detection and evaluation
critetia. Our analysis is based on a Bayesian model selection between two
competing models: one with and one without an eclipse signal. The search is
carried out by mapping the Bayes factor in favor of the eclipse model as a
function of the eclipse center time, after which the characterization of
plausible eclipse candidates is done by estimating the posterior distributions
of the eclipse model parameters using Markov Chain Monte Carlo.
We discover statistically significant eclipse events for two planets,
CoRoT-6b and CoRoT-11b, and for one brown dwarf, CoRoT-15b. We also find
marginally significant eclipse events passing our plausibility criteria for
CoRoT-3b, 13b, 18b, and 21b. The previously published CoRoT-1b and CoRoT-2b
eclipses are also confirmed.
In this letter we carry out the first systematic investigation of the expected gravitational wave (GW) background generated by supermassive black hole (SMBH) binaries in the nHz frequency band accessible to pulsar timing arrays (PTAs). We take from the literature several estimates of the redshift dependent galaxy mass function and of the fraction of close galaxy pairs to derive a wide range of galaxy merger rates. We then exploit empirical black hole-host relations to populate merging galaxies with SMBHs. The result of our procedure is a collection of a large number of phenomenological SMBH binary merger rates consistent with current observational constraints on the galaxy assembly at z<1.5. For each merger rate we compute the associated GW signal, eventually producing a large set of estimates of the nHz GW background that we use to infer confidence intervals of its expected amplitude. When considering the most recent SMBH-host relations, accounting for ultra-massive black holes in brightest cluster galaxies, we find that the nominal $1\sigma$ interval of the expected GW signal is only a factor of 3-to-10 below current PTA limits, implying a non negligible chance of detection in the next few years.
We introduce a novel implementation of orbit-based (or Schwarzschild) modeling that allows dark matter density profiles to be calculated non-parametrically in nearby galaxies. Our models require no assumptions to be made about velocity anisotropy or the dark matter profile. The technique can be applied to any dispersion-supported stellar system, and we demonstrate its use by studying the Local Group dwarf spheroidal (dSph) galaxy Draco. We use existing kinematic data at larger radii and also present 12 new radial velocities within the central 13 pc obtained with the VIRUS-W integral field spectrograph on the 2.7m telescope at McDonald Observatory. Our non-parametric Schwarzschild models find strong evidence that the dark matter profile in Draco is cuspy for 20 < r < 700 pc. The profile for r > 20 pc is well-fit by a power law with slope \alpha=-1.0 +/- 0.2, consistent with predictions from Cold Dark Matter (CDM) simulations. Our models confirm that, despite its low baryon content relative to other dSphs, Draco lives in a massive halo.
We present a model for merger-driven evolution of the mass function for massive galaxies and their central supermassive black holes at late times. We discuss the current observational evidence in favor of merger-driven massive galaxy evolution during this epoch, and demonstrate that the observed evolution of the mass function can be reproduced by evolving an initial mass function under the assumption of negligible star formation. We calculate the stochastic gravitational wave signal from the resulting black-hole binary mergers in the low redshift universe (z < 1) implied by this model, and find that this population has a signal-to-noise ratio as much as ~5x larger than previous estimates for pulsar timing arrays, with an expectation value for the characteristic strain h_c(f =1 yr^{-1})=5.8 x 10^{-15} that is already in tension with observational constraints, and a 2-sigma lower limit within this model of h_c(f =1 yr^{-1})=2.0 x 10^{-15}. The strength of this signal may therefore be detectable with the data already collected using the current generation of pulsar timing arrays, and could be detected with high statistical significance under conservative assumptions within the next few years, if the principle assumption of merger-driven galaxy evolution since z=1 holds true. For cases where a galaxy merger fails to lead to a black hole merger, we estimate the probability for a given number of satellite unmerged black holes to remain within a massive host galaxy, and interpret the result in light of ULX observations. In particular, we find that the brightest cluster galaxies should have 1-2 such sources with luminosities above 10^{39} erg/s, which is consistent with the statistics of observed ULXs.
Using 5 GHz radio luminosity at light-curve maximum as a proxy for jet power and black-hole spin measurements obtained via the continuum-fitting method, Narayan & McClintock (2012) presented the first direct evidence for a relationship between jet power and black hole spin for four transient black-hole binaries. We test and confirm their empirical relationship using a fifth source, H1743-322, whose spin was recently measured. We show that this relationship is consistent with Fe-line spin measurements provided that the black hole spin axis is assumed to be aligned with the binary angular momentum axis. We also show that, during a major outburst of a black hole transient, the system reasonably approximates an X-ray standard candle. We further show, using the standard synchrotron bubble model, that the radio luminosity at light-curve maximum is a good proxy for jet kinetic energy. Thus, the observed tight correlation between radio power and black hole spin indicates a strong underlying link between mechanical jet power and black hole spin. Using the fitted correlation between radio power and spin for the above five calibration sources, we predict the spins of six other black holes in X-ray/radio transient systems with low-mass companions. Remarkably, these predicted spins are all relatively low, especially when compared to the high measured spins of black holes in persistent, wind-fed systems with massive companions.
We present a new way to formulate the geometry of the Cosmic Web in terms of Lagrangian space. The Adhesion model has an ingenious geometric interpretation out of which the spine of the Cosmic Web emerges naturally. Within this context we demonstrate a deep connection of the relation between Eulerian and Lagrangian space with that between Voronoi and Delaunay tessellations.
The study of high-magnetic-field pulsars is important for examining the relationships between radio pulsars, magnetars, and X-ray-isolated neutron stars (XINSs). Here we report on X-ray observations of three such high-magnetic-field radio pulsars. We first present the results of a deep XMM-Newton observation of PSR J1734-3333, taken to follow up on its initial detection in 2009. The pulsar's spectrum is well fit by a blackbody with a temperature of 300 +/- 60 eV, with bolometric luminosity L_bb = 2.0(+2.2 -0.7)e+32 erg/s = 0.0036E_dot for a distance of 6.1 kpc. We detect no X-ray pulsations from the source, setting a 1 sigma upper limit on the pulsed fraction of 60% in the 0.5-3 keV band. We compare PSR J1734-3333 to other rotation-powered pulsars of similar age and find that it is significantly hotter, supporting the hypothesis that the magnetic field affects the observed thermal properties of pulsars. We also report on XMM-Newton and Chandra observations of PSRs B1845-19 and J1001-5939. We do not detect either pulsar, setting 3 sigma upper limits on their blackbody temperatures of 48 and 56 eV, respectively. Despite the similarities in rotational properties, these sources are significantly cooler than all but one of the XINSs, which we attribute to the two groups having been born with different magnetic fields and hence evolving differently.
We propose that the energetic major outburst of the supernovae (SN) impostor SN 2009ip in September 2012 (outburst 2012b) was a mergerburst event, where two massive stars merged. The previous outbursts of 2009 and 2011 occurred during near periastron passages of the binary system prior to the merger, in a similar manner to the luminosity peaks in the ninetieth century Great Eruption of the massive binary system Eta Carinae. The major 2012b outburst and the 2012a pre-outburst, resemble the light curve of the mergerburst event V838 Mon. A merger of stars with masses of M_1~100Mo and M_2~0.2-0.4M_1 can account for the energy of SN 2009ip. The ejected nebula is expected to have a bipolar structure. The observed fast blue-shifted absorption suggests that we observe the system along the polar direction.
The nature of the recently detected HE and VHE gamma-ray emission of Tycho's supernova remnant (SNR) is studied. A nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is employed to investigate the properties of Tycho's SNR and their correspondence to the existing experimental data, taking into account that the ambient interstellar medium (ISM) is expected to be clumpy. It is demonstrated that the overall steep gamma-ray spectrum observed can be interpreted as the superposition of two spectra produced by the CR proton component in two different ISM phases: The first gamma-ray component, extending up to about $10^{14}$ eV, originates in the diluted warm ISM, whereas the second component, extending up to 100 GeV, comes from numerous dense, small-scale clouds embedded in this warm ISM. Given the consistency between acceleration theory and the observed properties of the nonthermal emission of Tycho's SNR, a very efficient production of nuclear CRs in Tycho's SNR is established. The excess of the GeV gamma-ray emission due to the clouds' contribution above the level expected in the case of a purely homogeneous ISM, is inevitably expected in the case of type Ia SNe.
In order to understand the physical mechanisms underlying non-steady stellar spiral arms in disk galaxies, we analyzed the growing and damping phases of their spiral arms using three-dimensional $N$-body simulations. We confirmed that the spiral arms are formed due to a swing amplification mechanism that reinforces density enhancement as a seeded wake. In the damping phase, the Coriolis force exerted on a portion of the arm surpasses the gravitational force that acts to shrink the portion. Consequently, the stars in the portion escape from the arm, and subsequently they form a new arm at a different location. The time-dependent nature of the spiral arms are originated in the continual repetition of this non-linear phenomenon. Since a spiral arm does not rigidly rotate, but follows the galactic differential rotation, the stars in the arm rotate at almost the same rate as the arm. In other words, every single position in the arm can be regarded as the co-rotation point. Due to interaction with their host arms, the energy and angular momentum of the stars change, thereby causing the radial migration of the stars. During this process, the kinetic energy of random motion (random energy) of the stars does not significantly increase, and the disk remains dynamically cold. Owing to this low degree of disk heating, the short-lived spiral arms can recurrently develop over many rotational periods. The resultant structure of the spiral arms in the $N$-body simulations is consistent with some observational nature of spiral galaxies. We conclude that the formation and structure of spiral arms in isolated disk galaxies can be reasonably understood by non-linear interactions between a spiral arm and its constituent stars.
A search for light dark matter using low-threshold data from the single phase liquid xenon scintillation detector XMASS, has been conducted. Using the entire 835 kg inner volume as target, the analysis threshold can be lowered to 0.3 keVee (electron-equivalent) to search for light dark matter. With low-threshold data corresponding to a 5591.4 kg$\cdot$day exposure of the detector and without discriminating between nuclear-recoil and electronic events, XMASS sets an upper limit on the WIMP-nucleon cross section for WIMPs with masses below 20 GeV and excludes part of the parameter space allowed by other experiments.
The Chinese Area Positioning System (CAPS), a navigation system based on GEO communication satellites, was developed in 2002 by astronomers at Chinese Academy of Sciences. Extensive positioning experiments of CAPS have been performed since 2005. On the basis of CAPS, this paper studies the principle of navigation constellation composed of Slightly Inclined Geostationary Orbit (SIGSO) communication satellites. SIGSO satellites are derived from end-of-life Geostationary Orbit (GEO) satellites under inclined orbit operation. Considering the abundant frequency resources of SIGSO satellites, multi-frequency observations could be conducted to enhance the precision of pseudorange measurements and ameliorate the positioning performence. The constellation composed of two GEO satellites and four SIGSO satellites with inclination of 5 degrees can provide the most territory of China with 24-hour maximum PDOP less than 42. With synthetic utilization of the truncated precise (TP) code and physical augmentation factor in four frequencies, navigation system with this constellation is expected to obtain comparable positioning performance with that of coarse acquisition code of GPS. When the new approach of code-carrier phase combinations is adopted, the system has potential to possess commensurate accuracy of precise code in GPS. Additionally, the copious frequency resources can also be used to develop new anti-interference techniques and integrate navigation and communication.
(shortened) We perform 3D hydrodynamic simulations of gas flowing around a planetary core of mass \mplan=10\me embedded in a near Keplerian background flow, using a modified shearing box approximation. We employ a nested grid hydrodynamic code with as many as six nested grids, providing spatial resolution on the finest grid comparable to the present day diameters of Neptune and Uranus. We find that a strongly dynamically active flow develops such that no static envelope can form. The activity is not sensitive to plausible variations in the rotation curve of the underlying disk. It is sensitive to the thermodynamic treatment of the gas, as modeled by prescribed equations of state (either `locally isothermal' or `locally isentropic') and the temperature of the background disk material. The activity is also sensitive to the shape and depth of the core's gravitational potential, through its mass and gravitational softening coefficient. The varying flow pattern gives rise to large, irregular eruptions of matter from the region around the core which return matter to the background flow: mass in the envelope at one time may not be found in the envelope at any later time. The angular momentum of material in the envelope, relative to the core, varies both in magnitude and in sign on time scales of days to months near the core and on time scales a few years at distances comparable to the Hill radius. We show that material entering the dynamically active environment may suffer intense heating and cooling events the durations of which are as short as a few hours to a few days. Peak temperatures in these events range from $T \sim 1000$ K to as high as $T \sim 3-4000$ K, with densities $\rho\sim 10^{-9}-10^{-8}$ g/cm$^3$. These time scales, densities and temperatures span a range consistent with those required for chondrule formation in the nebular shock model.
The possibility of non-axisimmetric (kink) instabilities of a toroidal field seated in the tachocline is much discussed in the literature. In this work, the basic properties of kink and quasi-interchange instabilities, produced by mixed toroidal and poloidal configuration, will be briefly reviewed. In particular it will be shown that the unstable modes are strongly localized near the Equator and not near the Poles as often claimed in the literature. Based on the results of recent numerical simulations, it is argued that a non-zero helicity can already be produced at a non-linear level. A mean-field solar dynamo is then constructed with a positive $\alpha$-effect in the overshoot layer localized near the Equator and a meridional circulation with a deep return flow. Finally, the possibility that the solar cycle is driven by a $\alpha\Omega$ dynamo generated by the negative subsurface shear in the supergranulation layer will also be discussed.
In December 2012, Austria will launch its first two satellites: UniBRITE and BRITE-Austria. This is the first pair of three, forming a network called BRITE-Constellation. The other pairs being contributed by Canada and Poland. The primary goal of BRITE-Constellation is the exploration of short term intensity variations of bright stars (V>6 mag) for a few years. For each satellite pair, one will employ a blue filter and the other a red filter. With the discovery of the first exoplanet in 1992, more than 800 have been detected since. The high-precision photometry from the BRITE instrument will enable a transit search for exoplanets around bright stars. To estimate the capability of BRITE to detect planets, we include in our calculations technical constraints, such as photometric noise levels for stars accessible by BRITE, the duty cycle and duration of observations. The most important parameter is the fraction of stars harboring a planet. Our simulation is based on 2695 stars distributed over the entire sky. Kepler data indicate that at minimum 34% of all stars are orbited by at least one of five different planetary sizes: Earth, Super-Earth, Uranus, Jupiter and Super-Jupiter. Depending on the duty cycle and duration of the observations, about six planets should be detectable in 180 days, of which about five of them being of Jupiter size.
We present preliminary results obtained from analysis of the VI photometry of the globular cluster M79. Stellar variability survey performed with the image subtraction method yielded six new pulsating stars: two of RR Lyrae type, three SX Phoenicis stars and even one W Virginis star. Using all eleven RR Lyrae stars known in the cluster we find that M79 is Oosterhoff type II globular cluster.
We compiled a list of about 250 SX Phoenicis stars known in Galactic globular clusters in order to study period-luminosity relation for this type of variable. The absolute magnitudes of these stars are derived using metallicity-luminosity calibration for RR Lyrae stars. The mixture of different radial and non-radial modes present in SX Phoenicis stars and the lack of unique method of mode identification cause the difficulties in defining strict period-luminosity relation. As a solution we propose to use confirmed double-mode radial pulsators.
The moss is the area at the footpoint of the hot (3 to 5 MK) loops forming the core of the active region where emission is believed to result from the heat flux conducted down to the transition region from the hot loops. Studying the variation of Doppler shift as a function of line formation temperatures over the moss area can give clues on the heating mechanism in the hot loops in the core of the active regions. We investigate the absolute Doppler shift of lines formed at temperatures between 1 MK and 2 MK in a moss area within active region NOAA 11243 using a novel technique that allows determining the absolute Doppler shift of EUV lines by combining observations from the SUMER and EIS spectrometers. The inner (brighter and denser) part of the moss area shows roughly constant blue shift (upward motions) of 5 km/s in the temperature range of 1 MK to 1.6 MK. For hotter lines the blue shift decreases and reaches 1 km/s for Fe xv 284 {\AA} (~2 MK). The measurements are discussed in relation to models of the heating of hot loops. The results for the hot coronal lines seem to support the quasi-steady heating models for non-symmetric hot loops in the core of active regions.
We present a multi-purpose genetic algorithm, designed and implemented with GPGPU / CUDA parallel computing technology. The model was derived from a multi-core CPU serial implementation, named GAME, already scientifically successfully tested and validated on astrophysical massive data classification problems, through a web application resource (DAMEWARE), specialized in data mining based on Machine Learning paradigms. Since genetic algorithms are inherently parallel, the GPGPU computing paradigm has provided an exploit of the internal training features of the model, permitting a strong optimization in terms of processing performances and scalability.
I present some insights into Hanny's Voorwerp and the Antikythera mechanism - contrasting their similarities and differences. They are both excellent examples of serendipitous discoveries in which human curiosity and perseverance have played an important role. Both objects have captured the imagination of the general public, and their discovery was only made possible via the introduction of new technologies. One major difference is that there is only one Antikythera device but there are now many Voorwerpen or "voorwerpjes", as they are more commonly known. The study of a collection of objects, as is common in astronomy, greatly aids our understanding of cosmic phenomena. In the case of the voorwepjes, we now know that such systems are to be identified with obscured galaxies or Active Galactic Nuclei (AGN) that appear to have recently and indeed rapidly turned off. Clearly, the discovery of more examples of devices similar to the Antikythera mechanism would have a significant affect in advancing our understanding of this object and the people that constructed it. Thus far, surveys of the site of the Antikythera wreck are incomplete and non-systematic. Like radio astronomy and other progressive fields, technological advances proceed exponentially in terms of capacity and capability. Recent advances in diving technology are no exception to this rule. It is almost 40 years ago that Jacques Cousteau led the last adhoc survey of the Antikythera wreck - the time has surely come to revisit the site and conduct a proper scientific and systematic survey. The deepest areas of the site are so far completely unexplored while it is known that some artefacts did fall into this area during the original excavation. During this workshop, I called for a return to the site using the most modern diving technologies.
This paper presents an orbital analysis of six southern single-lined
spectroscopic binary systems. The systems selected were shown to have circular
or nearly circular orbits (e < 0.1) from earlier published solutions of only
moderate precision. The purpose was to obtain high-precision orbital solutions
in order to investigate the presence of small non-Keplerian velocity effects in
the data and hence the reality of the small eccentricities found for most of
the stars.
The Hercules spectrograph and 1-m McLellan telescope at Mt John Observatory,
New Zealand, were used to obtain over 450 CCD spectra between 2004 October and
2007 August. Radial velocities were obtained by cross-correlation. These data
were used to achieve high-precision orbital solutions for all the systems
studied, sometimes with solutions up to about 50 times more precise than those
from the earlier literature. However, the precision of the solutions is limited
in some cases by the rotational velocity or chromospheric activity of the
stars.
The data for the six binaries analysed here are combined with those for six
stars analysed earlier by Komonjinda, Hearnshaw and Ramm.We have performed
tests using the prescription of Lucy on all 12 binaries, and conclude that,
with one exception, none of the small eccentricities found by fitting Keplerian
orbits to the radial-velocity data can be supported. Instead we conclude that
small non-Keplerian effects, which are clearly detectable for six of our stars,
make impossible the precise determination of spectroscopic binary orbital
eccentricities for many late-type stars to better than about 0.03 in
eccentricity, unless the systematic perturbations are also carefully modelled.
The magnitudes of the non-Keplerian velocity variations are given
quantitatively.
Aims. Excitation of far-infrared and submillimetric molecular lines may originate from nonreactive collisions, chemical formation, or far infrared, near-infrared, and optical fluorescences. As a template, we investigate the impact of each of these processes on the excitation of the methylidyne cation CH+ and on the intensities of its rotational transitions recently detected in emission in dense photodissociation regions (PDRs) and in planetary nebulae. Methods. We have developed a nonlocal thermodynamic equilibrium (non-LTE) excitation model that includes the entire energy structure of CH+, i.e. taking into account the pumping of its vibrational and bound and unbound electronic states by near-infrared and optical photons. The model includes the theoretical cross-sections of nonreactive collisions with H, H2, He, and e-, and a Boltzmann distribution is used to describe the probability of populating the excited levels of CH+ during its chemical formation by hydrogenation of C+. To confirm our results we also performed an extensive analytical study, which we use to predict the main excitation process of several diatomic molecules, namely HF, HCl, SiO, CS, and CO. Results. At densities nH = 10^4 cm-3, the excitation of the rotational levels of CH+ is dominated by the radiative pumping of its electronic, vibrational, and rotational states if the intensities of the radiation field at \sim 0.4, \sim 4, and \sim 300 \mum are stronger than 10^5, 10^8, and 10^4 times those of the local interstellar radiation field (ISRF). Below these values, the chemical pumping is the dominant source of excitation of the J > 1 levels, even at high kinetic temperatures (\sim 1000 K). The far-infrared emission lines of CH+ observed in the Orion Bar and the NGC 7027 PDRs are consistent with the predictions of our excitation model assuming an incident far-ultraviolet (FUV) radiation field of \sim 3 \times 10^4 (in Draine's unit) and densities of \sim 5 \times 10^4 and \sim 2 \times 10^5 cm-3. In the case of NGC 7027, the estimate of the density is 10 to 100 times lower than those deduced by traditional excitation codes. Applying our model to other X1\Sigma+ ground state diatomic molecules, we find that HF, and SiO and HCl are the species the most sensitive to the radiative pumping of their vibrational and bound electronic states. In both cases, the minimal near-infrared and optical/UV radiation field intensities required to modify their rotational level populations are \sim 10^3 times those of the local ISRF at densities nH = 10^4 cm-3. All these results point towards interstellar and circumstellar media with densities lower than previously established and cast doubts on the clumpiness of well-studied molecular clouds.
It is often claimed that there is not only one, but two different types of solar dynamos: the one that is responsible for the appearance of sunspots and the 11-yr cycle, frequently referred to as the "global dynamo", and a statistically time-invariant dynamo, generally referred to as the "local dynamo", which is supposed to be responsible for the ubiquitous magnetic structuring observed at small scales. Here we examine the relative contributions of these two qualitatively different dynamos to the small-scale magnetic flux, with the following conclusion: The local dynamo does not play a significant role at any of the spatially resolved scales, nearly all the small-scale flux, including the flux revealed by Hinode, is supplied by the global dynamo. This conclusion is reached by careful determination of the Sun's noise-corrected basal magnetic flux density while making use of a flux cancellation function determined from Hinode data. The only allowed range where there may be substantial or even dominating contributions from a local dynamo seems to be the scales below about 10 km, as suggested by observations of the Hanle depolarization effect in atomic spectral lines. To determine the fraction of the Hanle depolarization that may be due to the action of a local dynamo, a synoptic program is being initiated at IRSOL (Istituto Ricerche Solari Locarno).
TIRCAM2 (TIFR Near Infrared Imaging Camera - II) is a closed cycle cooled imager that has been developed by the Infrared Astronomy Group at the Tata Institute of Fundamental Research for observations in the near infrared band of 1 to 3.7 microns with existing Indian telescopes. In this paper, we describe some of the technical details of TIRCAM2 and report its observing capabilities, measured performance and limiting magnitudes with the 2-m IUCAA Girawali telescope and the 1.2-m PRL Gurushikhar telescope. The main highlight is the camera's capability of observing in the nbL (3.59 microns) band enabling our primary motivation of mapping of Polycyclic Aromatic Hydrocarbon (PAH) emission at 3.3 microns.
The near-infrared (NIR) wavelength range offers some unique spectral features, and it is less prone to the extinction than the optical one. Recently, the first flux calibrated NIR library of cool stars from the NASA Infrared Telescope Facility (IRTF) have become available, and it has not been fully exploited yet. We want to develop spectroscopic diagnostics for stellar physical parameters based on features in the wavelength range 1-5 micron. In this work we test the technique in the I and K bands. The study of the Y, J, H, and L bands will be presented in the following paper. An objective method for semi-empirical definition of spectral features sensitive to various physical parameters is applied to the spectra. It is based on sensitivity map--i.e., derivative of the flux in the spectra with respect to the stellar parameters at a fixed wavelength. New optimized indices are defined and their equivalent widths (EWs) are measured. A number of sensitive features to the effective temperature and surface gravity are re-identified or newly identified clearly showing the reliability of the sensitivity map analysis. The sensitivity map allows to identify the best bandpass limits for the line and nearby continuum. It reliably predicts the trends of spectral features with respect to a given physical parameter but not their absolute strengths. Line blends are easy to recognize when blended features have different behavior with respect to some physical stellar parameter. The use of sensitivity map is therefore complementary to the use of indices. We give the EWs of the new indices measured for the IRTF star sample. This new and homogeneous set of EWs will be useful for stellar population synthesis models and can be used to get element-by-element abundances for unresolved stellar population studies in galaxies.
A Baker-Nunn Camera (BNC), originally installed at the Real Instituto y
Observatorio de la Armada (ROA) in 1958, was refurbished and robotized. The new
facility, called Telescope Fabra ROA Montsec (TFRM), was installed at the
Observatori Astron\`omic del Montsec (OAdM).
The process of refurbishment is described in detail. Most of the steps of the
refurbishment project were accomplished by purchasing commercial components,
which involve little posterior engineering assembling work. The TFRM is a 0.5m
aperture f/0.96 optically modified BNC, which offers a unique combination of
instrumental specifications: fully robotic and remote operation, wide-field of
view (4.4 deg x 4.4 deg), moderate limiting magnitude (V~19.5mag), ability of
tracking at arbitrary right ascension and declination rates, as well as opening
and closing CCD shutter at will during an exposure.
Nearly all kind of image survey programs can benefit from those
specifications. Apart from other less time consuming programs, since the
beginning of science TFRM operations we have been conducting two specific and
distinct surveys: super-Earths transiting around M-type dwarfs stars, and
geostationary debris in the context of Space Situational Awareness / Space
Surveillance and Tracking (SSA/SST) programs. Preliminary results for both
cases will be shown.
The relationship between the clustering of dark matter and that of luminous matter is often described using the bias parameter. Here, we provide a new method to probe the bias of intermediate to high-redshift radio continuum sources for which no redshift information is available. We matched radio sources from the Faint Images of the Radio Sky at Twenty centimetres (FIRST) survey data to their optical counterparts in the Sloan Digital Sky Survey (SDSS) to obtain photometric redshifts for the matched radio sources. We then use the publicly available semi-empirical simulation of extragalactic radio continuum sources (S3) to infer the redshift distribution for all FIRST sources and estimate the redshift distribution of unmatched sources by subtracting the matched distribution from the distribution of all sources. We infer that the majority of unmatched sources are at higher redshifts than the optically matched sources and demonstrate how the angular scales of the angular two-point correlation function can be used to probe different redshift ranges. We compare the angular clustering of radio sources with that expected for dark matter and estimate the bias of different samples.
The latest XENON100 data severely constrains dark matter elastic scattering off nuclei, leading to impressive upper limits on the spin-independent cross-section. The main goal of this paper is to stress that the same data set has also an excellent \emph{spin-dependent} sensitivity, which is of utmost importance in probing dark matter models. We show in particular that the constraints set by XENON100 on the spin-dependent neutron cross-section are by far the best at present, whereas the corresponding spin-dependent proton limits lag behind other direct detection results. The effect of nuclear uncertainties on the structure functions of xenon isotopes is analysed in detail and found to lessen the robustness of the constraints, especially for spin-dependent proton couplings. Notwithstanding, the spin-dependent neutron prospects for XENON1T and DARWIN are very encouraging. We apply our constraints to well-motivated dark matter models and demonstrate that in both mass-degenerate scenarios and the minimal supersymmetric standard model the spin-dependent neutron limits can actually override the spin-independent limits. This opens the possibility of probing additional unexplored regions of the dark matter parameter space with the next generation of ton-scale direct detection experiments.
We reinvestigate the scenario that the amount of the baryons and the gravitino dark matter is naturally explained by the decay of the Q balls in the gauge-mediated SUSY breaking. Equipped by the more correct decay rates into gravitinos and baryons recently derived, we find that the scenario with the direct production of the gravitino dark matter from the Q-ball decay works naturally.
Motivated by recent claims of lines in the Fermi gamma-ray spectrum, we critically examine means of enhancing neutralino annihilation into neutral gauge bosons. The signal can be boosted while remaining consistent with continuum photon constraints if a new singlet-like pseudoscalar is present. We consider singlet extensions of the MSSM, focusing on the NMSSM, where a `well-tempered' neutralino can explain the lines while remaining consistent with current constraints. We adopt a complementary numerical and analytic approach throughout in order to gain intuition for the underlying physics. The scenario requires a rich spectrum of light neutralinos and charginos leading to characteristic phenomenological signatures at the LHC whose properties we explore. Future direct detection prospects are excellent, with sizeable spin-dependent and spin-independent cross-sections.
We investigate the finite temperature expectation values of the charge and current densities for a complex scalar field with nonzero chemical potential in background of a flat spacetime with spatial topology $R^{p}\times (S^{1})^{q}$. Along compact dimensions quasiperiodicity conditions with general phases are imposed on the field. In addition, we assume the presence of a constant gauge field which, due to the nontrivial topology of background space, leads to Aharonov-Bohm-like effects on the expectation values. By using the Abel-Plana-type summation formula and zeta function techniques, two different representations are provided for both the current and charge densities. The current density has nonzero components along the compact dimensions only and, in the absence of a gauge field, it vanishes for special cases of twisted and untwisted scalar fields. In the high-temperature limit, the current density and the topological part in the charge density are linear functions of the temperature. The Bose-Einstein condensation for a fixed value of the charge is discussed. The expression for the chemical potential is given in terms of the lengths of compact dimensions, temperature and gauge field. It is shown that the parameters of the phase transition can be controlled by tuning the gauge field. The separate contributions to the charge and current densities coming from the Bose-Einstein condensate and from excited states are also investigated.
Photoionization of Kr$^+$ ions was studied in the energy range from 23.3 eV to 39.0 eV at a photon energy resolution of 7.5 meV. Absolute measurements were performed by merging beams of Kr$^+$ ions and of monochromatized synchrotron undulator radiation. Photoionization (PI) of this Br-like ion is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionization continuum. Resonance features observed in the experimental spectra are spectroscopically assigned and their energies and quantum defects tabulated. The high-resolution cross-section measurements are benchmarked against state-of-the-art theoretical cross-section calculations from the Dirac-Coulomb R-matrix method.
The acceleration of the expansion of the Universe has led to the construction of Dark Energy models where a light scalar field may have a range reaching up to cosmological scales. Screening mechanisms allow these models to evade the tight gravitational tests in the solar system and the laboratory. I will briefly review some of the salient features of screened modified gravity models of the chameleon, dilaton or symmetron types using $f(R)$ gravity as a template.
Despite over 35 years of constant satellite-based measurements of cloud, reliable evidence of a long-hypothesized link between changes in solar activity and Earth's cloud cover remains elusive. This work examines evidence of a cosmic ray cloud link from a range of sources, including satellite-based cloud measurements and long-term ground-based climatological measurements. The satellite-based studies can be divided into two categories: 1) monthly to decadal timescale correlations, and 2) daily timescale epoch-superpositional (composite) analysis. The latter analyses frequently focus on high-magnitude reductions in the cosmic ray flux known as Forbush Decrease (FD) events. At present, two long-term independent global satellite cloud datasets are available (ISCCP and MODIS). Although the differences between them are considerable, neither shows evidence of a solar-cloud link at either long or short timescales. Furthermore, reports of observed correlations between solar activity and cloud over the 1983 to 1995 period are attributed to the chance agreement between solar changes and artificially induced cloud trends. It is possible that the satellite cloud datasets and analysis methods may simply be too insensitive to detect a small solar signal. Evidence from ground-based studies suggests that some weak but statistically significant CR-cloud relationships may exist at regional scales, involving mechanisms related to the global electric circuit. However, a poor understanding of these mechanisms and their effects on cloud make the net impacts of such links uncertain. Regardless of this, it is clear that there is no robust evidence of a widespread link between the cosmic ray flux and clouds.
Low Energy solar neutrino detection plays a fundamental role in understanding both solar astrophysics and particle physics. After introducing the open questions on both fields, we review here the major results of the last two years and expectations for the near future from Borexino, Super-Kamiokande, SNO and KamLAND experiments as well as from upcoming (SNO+) and planned (LENA) experiments. Scintillator neutrino detectors are also powerful antineutrino detectors such as those emitted by the Earth crust and mantle. First measurements of geo-neutrinos have occurred and can bring fundamental contribution in understanding the geophysics of the planet.
In polyatomic molecules with \Pi\ electronic ground state the ro-vibrational spectrum can be strongly modified by the Renner-Teller effect. The linear form of C3H molecule has particularly strong Renner-Teller interaction and a very low lying vibronic \Sigma+ level, which corresponds to the excited bending vibrational mode. This leads to the increased sensitivities of the microwave and submillimeter transition frequencies to the possible variation of the fine structure constant alpha and electron to proton mass ratio mu.
Horndeski derived a most general vector-tensor theory in which the vector field respects the gauge symmetry and the resulting dynamical equations are of second order. The action contains only one free parameter, $\lambda$, that determines the strength of the non-minimal coupling between the gauge field and gravity. We investigate the cosmological consequences of this action and discuss observational constraints. For $\lambda<0$ we identify singularities where the deceleration parameter diverges within a finite proper time. This effectively rules out any sensible cosmological application of the theory for a negative non-minimal coupling. We also find a range of parameter that gives a viable cosmology and study the phenomenology for this case. Observational constraints on the value of the coupling are rather weak since the interaction is higher-order in space-time curvature.
We discuss asymmetric or symmetric dark matter candidate in the supersymmetric Dirac leptogenesis scenario. By introducing a singlet superfield coupling to right-handed neutrinos, the overabundance problem of dark matter can be evaded and various possibilities for dark matter candidate arise. If the singlino is the lightest supersymmetric particle (LSP), it becomes naturally asymmetric dark matter. On the other hand, the right-handed sneutrino is a symmetric dark matter candidate whose relic density can be determined by the usual thermal freeze-out process. The conventional neutralino or gravitino LSP can be also a dark matter candidate as its non-thermal production from the right-handed sneutrino can be controlled appropriately. In our scenario, the late-decay of heavy supersymmetric particles mainly produce the right-handed sneutrino and neutrino which is harmless to the standard prediction of the big-bang nucleosynthesis.
We have derived a non-Maxwellian molecular velocity distribution at large Knudsen numbers for ideal gas. This distribution approaches Maxwellian molecular velocity distribution as the Knudsen number approaches zero. We have found that the expectation value of the square of velocity is the same in the non-Maxwellian molecular velocity distribution as it is in the Maxwellian distribution; however, the expectation value of the speed is not the same.
During inflation, spacetime is approximately described by de Sitter space which is conformally invariant with the symmetry group SO(1,4). This symmetry can significantly constrain the quantum perturbations which arise in the inflationary epoch. We consider a general situation of single field inflation and show that the three point function involving two scalar modes and one tensor mode is uniquely determined, up to small corrections, by the conformal symmetries. Special conformal transformations play an important role in our analysis. Our result applies only to models where the inflaton sector also approximately preserves the full conformal group and shows that this three point function is a good way to test if special conformal invariance was preserved during inflation.
The ANTARES underwater neutrino telescope is located in the Mediterranean Sea about 40 km from Toulon at a depth of 2475 m. In its 12 line configuration it has almost 900 photomultipliers in 295 floors. The performance of the detector is discussed and several results are presented, including the measurements of downgoing muons, atmospheric neutrinos, search for a diffuse flux of high energy muon neutrinos, search for cosmic point sources of neutrinos, multi messenger astronomy, searches for fast magnetic monopoles and slow nuclearites. A short discussion is also made on Earth and Sea Science studies with a neutrino telescope.
We investigate the LHC sensitivity to supersymmetric models with light higgsinos, small R-parity breaking and gravitino dark matter. The limits on decaying gravitino dark matter from gamma-ray searches with the Fermi-LAT put a lower bound on the higgsino-like neutralino NLSP decay length, giving rise to a displaced-vertex collider signature. Using publicly available tools for simulation of signal, background and detector response, we find that higgsinos with masses of 100-400 GeV and R-parity violation of approximately 10^-8 to 10^-9 can show up in the 8 TeV LHC data with 10-30 fb^-1 of integrated luminosity. We demonstrate that in the case of a signal, the higgsino mass can be determined by reconstruction of the dimuon mass edge.
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The capture of a compact object in a galactic nucleus by a massive black hole (MBH), an extreme-mass ratio inspiral (EMRI), is the best way to map space and time around it. Recent work on stellar dynamics has demonstrated that there seems to be a complot in phase space acting on low-eccentricity captures, since their rates decrease significantly by the presence of a blockade in the rate at which orbital angular momenta change takes place. This so-called "Schwarzschild barrier" is a result of the impact of relativistic precession on to the stellar potential torques, and thus it affects the enhancement on lower-eccentricity EMRIs that one would expect from resonant relaxation. We confirm and quantify the existence of this barrier using a statistical sample of 2,500 direct-summation N-body simulations using both a post-Newtonian and also for the first time in a direct-summation code a geodesic approximation for the relativistic orbits. The existence of the barrier prevents low-eccentricity EMRIs from approaching the central MBH, but high-eccentricity EMRIs, which have been wrongly classified as "direct plunges" until recently, ignore the presence of the barrier, because they are driven by two-body relaxation. Hence, since the rates are significantly affected in the case of low-eccentricity EMRIs, we predict that a LISA-like observatory such as eLISA will predominantly detect high-eccentricity EMRIs.
We summarize the science opportunity, design elements, current and projected partner observatories, and anticipated science returns of the Astrophysical Multimessenger Observatory Network (AMON). AMON will link multiple current and future high-energy, multimessenger, and follow-up observatories together into a single network, enabling near real-time coincidence searches for multimessenger astrophysical transients and their electromagnetic counterparts. Candidate and high-confidence multimessenger transient events will be identified, characterized, and distributed as AMON alerts within the network and to interested external observers, leading to follow-up observations across the electromagnetic spectrum. In this way, AMON aims to evoke the discovery of multimessenger transients from within observatory subthreshold data streams and facilitate the exploitation of these transients for purposes of astronomy and fundamental physics. As a central hub of global multimessenger science, AMON will also enable cross-collaboration analyses of archival datasets in search of rare or exotic astrophysical phenomena.
The multiple-planet systems discovered by the Kepler mission exhibit the following feature: planet pairs near first-order mean-motion resonances prefer orbits just outside the nominal resonance, while avoiding those just inside the resonance. We explore an extremely simple dynamical model for planet formation, in which planets grow in mass at a prescribed rate without orbital migration or dissipation. We develop an analytic version of this model for two-planet systems in two limiting cases: the planet mass grows quickly or slowly relative to the characteristic resonant libration time. In both cases the distribution of systems in period ratio develops a characteristic asymmetric peak-trough structure around the resonance, qualitatively similar to that observed in the Kepler sample. We verify this result with numerical integrations of the restricted three-body problem. We show that for the 3:2 resonance, where the observed peak-trough structure is strongest, our simple model is consistent with the observations for a range of mean planet masses 20-100M_{\oplus}. This mass range is higher than expected, by at least a factor of three, from the few Kepler planets with measured masses, but part of this discrepancy could be due to oversimplifications in the dynamical model or uncertainties in the planetary mass-radius relation.
We examine unresolved nuclear X-ray sources in 57 brightest cluster galaxies to study the relationship between nuclear X-ray emission and accretion onto supermassive black holes (SMBHs). The majority of the clusters in our sample have prominent X-ray cavities embedded in the surrounding hot atmospheres, which we use to estimate mean jet power and average accretion rate onto the SMBHs over the past several hundred Myr. We find that ~50% of the sample have detectable nuclear X-ray emission. The nuclear X-ray luminosity is correlated with average accretion rate determined using X-ray cavities, which is consistent with the hypothesis that nuclear X-ray emission traces ongoing accretion. The results imply that jets in systems that have experienced recent AGN outbursts, in the last ~10^7yr, are `on' at least half of the time. Nuclear X-ray sources become more luminous with respect to the mechanical jet power as the mean accretion rate rises. We show that nuclear radiation exceeds the jet power when the mean accretion rate rises above a few percent of the Eddington rate, where the AGN apparently transitions to a quasar. The nuclear X-ray emission from three objects (A2052, Hydra A, M84) varies by factors of 2-10 on timescales of 6 months to 10 years. If variability at this level is a common phenomenon, it can account for much of the scatter in the relationship between mean accretion rate and nuclear X-ray luminosity. We find no significant change in the spectral energy distribution as a function of luminosity in the variable objects. The relationship between accretion and nuclear X-ray luminosity is consistent with emission from either a jet, an ADAF, or a combination of the two, although other origins are possible. We also consider the longstanding problem of whether jets are powered by the accretion of cold circumnuclear gas or nearly spherical inflows of hot keV gas.[abridged]
We place the most robust constraint to date on the scale of the turnover in the cosmological matter power spectrum using data from the WiggleZ Dark Energy Survey. We find this feature to lie at a scale of k_0=0.0160^{+0.0041}_{-0.0035}$ [h/Mpc] (68% confidence) for an effective redshift of 0.62 and obtain from this the first-ever turnover-derived distance and cosmology constraints: a measure of the cosmic distance-redshift relation in units of the horizon scale at the redshift of radiation-matter equality (r_H) of D_V(z=0.62)/r_H=18.3 (+6.3/-3.3) and, assuming a prior on the number of extra relativistic degrees of freedom N_eff=3, constraints on the cosmological matter density parameter Omega_Mh^2=0.136 (+0.026/-0.052) and on the redshift of matter-radiation equality z_eq=3274 (+631/-1260). All results are in excellent agreement with the predictions of standard LCDM models. Our constraints on the logarithmic slope of the power spectrum on scales larger than the turnover is bounded in the lower limit with values only as low as -1 allowed, with the prediction of standard LCDM models easily accommodated by our results. Lastly, we generate forecasts for the achievable precision of future surveys at constraining k_0, Omega_Mh^2, z_eq and N_eff. We find that the Baryon Oscillation Spectroscopic Survey should substantially improve upon the WiggleZ turnover constraint, reaching a precision on k_0 of {\pm}9% (68% confidence), translating to precisions on Omega_Mh^2 and z_eq of +/-10% (assuming a prior N_eff=3) and on N_eff of (+78/-56)% (assuming a prior Omega_Mh^2=0.135). This is sufficient precision to sharpen the constraints on N_eff from WMAP, particularly in its upper limit. For Euclid, we find corresponding attainable precisions on k_0, Omega_Mh^2, N_eff)$ of (3,4,+17/-21)%. This represents a precision approaching our forecasts for the Planck Surveyor. (Abridged)
We present an analysis of the 2-10 keV X-ray emission associated with the active galactic nuclei (AGNs) in brightest cluster galaxies (BCGs). Our sample consists of 32 BCGs that lie in highly X-ray luminous cluster of galaxies [L_X-ray(0.1-2.4 keV)>3*10^44 erg/s] in which AGN-jetted outflows are creating and sustaining clear X-ray cavities. Our sample covers the redshift range 0<z<0.6 and reveals strong evolution in the nuclear X-ray luminosities, such that the black holes in these systems have become on average at least 10 times fainter over the last 5 Gyrs. Mindful of the potential selection effects that may affect our results, we propose two possible scenarios to explain our results: 1) either that the AGNs in BCGs with X-ray cavities are steadily becoming fainter, or more likely, 2) that the fraction of these BCGs with radiatively efficient nuclei is decreasing with time from roughly 60 per cent at z~0.6 to 30 per cent at z~0.1. Based on this strong evolution, we predict that a significant fraction of BCGs in z~1 clusters may host quasars at their centres, potentially complicating the search for such clusters at high redshift. In analogy with black-hole binaries and based on the observed Eddington ratios of our sources, we further propose that the evolving AGN population in BCGs with X-ray cavities may be transiting from a canonical low/hard state analogous to that of X-ray binaries to a quiescent state over the last 5 Gyrs.
We examine the red fraction of central and satellite galaxies in the large zCOSMOS group catalog out to z ~ 0.8 correcting for both the incompleteness in stellar mass and for the less than perfect purities of the central and satellite samples. We show that, at all masses and at all redshifts, the fraction of satellite galaxies that have been quenched, i.e., are red, is systematically higher than that of centrals, as seen locally in the SDSS. The satellite quenching efficiency, which is the probability that a satellite is quenched because it is a satellite rather than a central, is, as locally, independent of stellar mass. Furthermore, the average value is about 0.5, which is also very similar to that seen in the SDSS. We also construct the mass functions of blue and red centrals and satellites and show that these broadly follow the predictions of the Peng et al. (2012) analysis of the SDSS groups. Together, these results indicate that the effect of the group environment in quenching satellite galaxies was very similar when the Universe was about a half its present age, as it is today.
The Cherenkov Telescope Array (CTA) \cite{CTA:2010} will be the successor to
current Imaging Atmospheric Cherenkov Telescopes (IACT) like H.E.S.S., MAGIC
and VERITAS. CTA will improve in sensitivity by about an order of magnitude
compared to the current generation of IACTs. The energy range will extend from
well below 100 GeV to above 100 TeV. To accomplish these goals, CTA will
consist of two arrays, one in each hemisphere, consisting of 50-80 telescopes
and composed of three different telescope types with different mirror sizes. It
will be the first open observatory for very high energy $\gamma$-ray astronomy.
The Array Control working group of CTA is currently evaluating existing
technologies which are best suited for a project like CTA. The considered
solutions comprise the ALMA Common Software (ACS), the OPC Unified Architecture
(OPC UA) and the Data Distribution Service (DDS) for bulk data transfer. The
first applications, like an automatic observation scheduler and the control
software for some prototype instrumentation have been developed.
Heavy fields coupled to the inflaton reduce the speed of sound in the effective theory of the adiabatic mode each time the background inflationary trajectory deviates from a geodesic. This can result in features in the primordial spectra. We compute the corresponding bispectrum and show that if a varying speed of sound induces features in the power spectrum, the change in the bispectrum is given by a simple formula involving the change in the power spectrum and its derivatives. In this manner, we provide a uniquely discriminable signature of a varying sound speed for the adiabatic mode during inflation that indicates the influence of heavy fields. We find that features in the bispectrum peak in the equilateral limit and, in particular, in the squeezed limit we find considerable enhancement entirely consistent with the single field consistency relation. From the perspective of the underlying effective theory, our results can be generalized to incorporate a wide variety of inflationary models where features are sourced by the time variation of background quantities.
Observations imply that long \gamma-ray bursts (GRBs) are originated from explosions of massive stars, therefore they may occur in the molecular clouds where their progenitors were born. We show here that the prompt optical-UV emission from GRBs may be delayed due to the dust extinction, which can well explain the observed optical delayed onset and fast rise in GRB 080319B. The density and the size of the molecular cloud around GRB 080319B are roughly constrained to be \sim10^3cm^{-3} and \sim 8pc, respectively. We also investigate the other GRBs with prompt optical-UV data, and find similar values of the densities and sizes of the local molecular clouds. The future observations of prompt optical-UV emission from GRBs in subsecond timescale, e.g., by UFFO-Pathfinder and SVOM-GWAC, will provide more evidence and probes of the local GRB environments.
A recent composite-dark-matter scenario assumes that the dominant fraction of dark matter consists of O-helium (OHe) dark atoms, in which a lepton-like doubly charged particle O is bound with a primordial helium nucleus. It liberates the physics of dark matter from unknown features of new physics, but it demands a deep understanding of the details of known nuclear and atomic physics, which are still unclear. Here, we consider in detail the physics of the binding of OHe to various nuclei of interest for direct dark matter searches. We show that standard quantum mechanics leads to bound states in the keV region, but does not seem to provide a simple mechanism that stabilizes them. The crucial role of a barrier in the OHe-nucleus potential is confirmed for such a stabilization.
To obtain a better statistics on the occurrence of magnetism among white dwarfs, we searched the spectra of the hydrogen atmosphere white dwarf stars (DAs) in the Data Release 7 of the Sloan Digital Sky Survey (SDSS) for Zeeman splittings and estimated the magnetic fields. We found 521 DAs with detectable Zeeman splittings, with fields in the range from around 1 MG to 733 MG, which amounts to 4% of all DAs observed. As the SDSS spectra have low signal-to-noise ratios, we carefully investigated by simulations with theoretical spectra how reliable our detection of magnetic field was.
We present deep Sparse Aperture Masking (SAM) observations obtained with the ESO Very Large Telescope of the pre-transitional disk object FL Cha (SpT=K8, d=160 pc), the disk of which is known to have a wide optically thin gap separating optically thick inner and outer disk components. We find non-zero closure phases, indicating a significant flux asymmetry in the K-band emission (e.g., a departure from a single point source detection). We also present radiative transfer modeling of the SED of the FL Cha system and find that the gap extends from ~0.06 to ~8.3 AU. We demonstrate that the non-zero closure phases can be explained almost equally well by starlight scattered off the inner edge of the outer disk or by a (sub)stellar companion. Single-epoch, single-wavelength SAM observations of transitional disks with large cavities that could become resolved should thus be interpreted with caution, taking the disk and its properties into consideration. In the context of a binary model, the signal is most consistent with a high-contrast (delta_K ~4.8 mag) source at a ~40 mas (6 AU) projected separation. However, the flux ratio and separation parameters remain highly degenerate and a much brighter source (deta_K ~1 mag) at 15 mas (2.4 AU) can also reproduce the signal. Second-epoch, multi-wavelength observations are needed to establish the nature of the SAM detection in FL Cha.
Some binary evolution scenarios to Type Ia supernovae include long-period binaries that evolve to symbiotic supersoft X-ray sources in their late stage of evolution. However, symbiotic stars with steady hydrogen burning on the white dwarf's (WD) surface are very rare, and the X-ray characteristics are not well known. SMC3 is one such rare example and a key object for understanding the evolution of symbiotic stars to Type Ia supernovae. SMC3 is an eclipsing symbiotic binary, consisting of a massive WD and red giant (RG), with an orbital period of 4.5 years in the Small Magellanic Cloud. The long-term V light curve variations are reproduced as orbital variations in the irradiated RG, whose atmosphere fills its Roche lobe, thus supporting the idea that the RG supplies matter to the WD at rates high enough to maintain steady hydrogen burning on the WD. We also present an eclipse model in which an X-ray emitting region around the WD is almost totally occulted by the RG swelling over the Roche lobe on the trailing side, although it is always partly obscured by a long spiral tail of neutral hydrogen surrounding the binary in the orbital plane.
Precision measurements of the polarization of the cosmic microwave background (CMB) radiation, especially experiments seeking to detect the odd-parity "B-modes", have far-reaching implications for cosmology. To detect the B-modes generated during inflation the Flux response and polarization angle of these experiments must be calibrated to exquisite precision. While suitable flux calibration sources abound, polarization angle calibrators are deficient in many respects. Man-made polarized sources are often not located in the antenna's far-field, have spectral properties that are radically different from the CMB's, are cumbersome to implement and may be inherently unstable over the (long) duration these searches require to detect the faint signature of the inflationary epoch. Astrophysical sources suffer from time, frequency and spatial variability, are not visible from all CMB observatories, and none are understood with sufficient accuracy to calibrate future CMB polarimeters seeking to probe inflationary energy scales of $10^{15}$ GeV. CMB $TB$ and $EB$ modes, expected to identically vanish in the standard cosmological model, can be used to calibrate CMB polarimeters. By enforcing the observed $EB$ and $TB$ power spectra to be consistent with zero, CMB polarimeters can be calibrated to levels not possible with man-made or astrophysical sources. All of this can be accomplished without any loss of observing time using a calibration source which is spectrally identical to the CMB B-modes. The calibration procedure outlined here can be used for any CMB polarimeter.
We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in normal star forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z~1.2 and 2.2, with log(M*(M_solar))>10.4 and log(SFR(M_solar/yr))>1.5. Including a correction for the incomplete coverage of the M*-SFR plane, we infer average gas fractions of ~0.33 at z~1.2 and ~0.47 at z~2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z~1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular gas - star formation relation for the z=1-3 SFGs is near-linear, with a ~0.7 Gyrs gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z~0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M*, gas fractions correlate strongly with the specific star formation rate. The variation of specific star formation rate between z~0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.
We use the infrared excess (IRX) FIR/UV luminosity ratio to study the relation between the effective UV attenuation (A_IRX) and the UV spectral slope (beta) in a sample of 450 1<z<2.5 galaxies. The FIR data is from very deep Herschel observations in the GOODS fields that allow us to detect galaxies with SFRs typical of galaxies with log(M)>9.3. Thus, we are able to study galaxies on and even below the main SFR-stellar mass relation (main sequence). We find that main sequence galaxies form a tight sequence in the IRX--beta plane, which has a flatter slope than commonly used relations. This slope favors a SMC-like UV extinction curve, though the interpretation is model dependent. The scatter in the IRX-beta plane, correlates with the position of the galaxies in the SFR-M plane. Using a smaller sample of galaxies with CO gas masses, we study the relation between the UV attenuation and the molecular gas content. We find a very tight relation between the scatter in the IRX-beta plane and the specific attenuation (S_A), a quantity that represents the attenuation contributed by the molecular gas mass per young star. S_A is sensitive to both the geometrical arrangement of stars and dust, and to the compactness of the star forming regions. We use this empirical relation to derive a method for estimating molecular gas masses using only widely available integrated rest-frame UV and FIR photometry. The method produces gas masses with an accuracy between 0.12-0.16 dex in samples of normal galaxies between z~0 and z~1.5. Major mergers and sub-millimeter galaxies follow a different S_A relation.
As part of the Herschel Guaranteed Time Key Programme CHESS, we present the discovery of a diffuse gas component in the foreground of the intermediate-mass protostar OMC-2 FIR 4, located in the Orion A region. Making use of the full HIFI spectrum of OMC-2 FIR 4 obtained in CHESS, we detected several ground-state lines from OH+, H2O+, HF, and CH+, all of them seen in absorption against the dust continuum emission of the protostar's envelope. The lines peak at a velocity of 9 km/s, which is blue-shifted by 2 km/s with respect to the systemic velocity of OMC-2 FIR 4 (V = 11.4 km/s). We derived column densities for each species, as well as an upper limit to the column density of the undetected H3O+. In order to model and characterise the foreground cloud, we used the Meudon PDR code to run a homogeneous grid of models that spans a reasonable range of densities, visual extinctions, cosmic ray ionisation rates and far-ultraviolet (FUV) radiation fields. The results of our modelling indicate that the foreground cloud is composed of predominantly neutral diffuse gas (n(H) = 100 cm-3) and is heavily irradiated by an external source of FUV that most likely arises from the nearby Trapezium OB association. The cloud is 6 pc thick and bears many similarities with the so-called C+ interface between Orion-KL and the Trapezium cluster, 2 pc south of OMC-2 FIR 4. We conclude that the foreground cloud we detected is an extension of the C+ interface seen in the direction of Orion KL, and interpret it to be the remains of the parental cloud of OMC-1, which extends from OMC-1 up to OMC-2.
We discuss NICOLE inversions of Fe I 630.15 nm and 630.25 nm Stokes spectra from a sunspot penumbra, recorded with the CRISP imaging spectropolarimeter at the Swedish 1-m Solar Telescope and a spatial resolution close to 0.15". Our emphasis is on narrow downflow lanes, which are cospatial with the relatively dark and cool parts of penumbral filaments. We find that these downflow lanes are located at the boundaries between areas of relatively horizontal magnetic field (the inter-spines) and much more vertical field (the spines). These locations agree with predictions from the convective gap model (the "gappy penumbra") proposed six years ago, and more recent 3D MHD simulations. We also find that in the deep photosphere, the downflow lanes are frequently, but not always, associated with opposite polarity magnetic field. This is also consistent with the simulations, predicting that many of the convective downflows pull down the magnetic field, rather than flow passively along it.
We present a new method to calculate formation of cosmological structure in
the Newtonian limit. The method is based on Lagrangian perturbation theory
(LPT) plus two key theoretical extensions. One advance involves fixing a
previously ignored gauge-like degree of freedom present in the formal LPT. The
traditional derivation of the perturbation expansion introduces this unwanted
freedom which it is crucial to eliminate. In effect, we transform the usual
results of a LPT calculation by a frame shift to give answers sought by a
particular observer. A second extension is based on our previous work where we
showed that, independent of orbit crossing, LPT expansions converge only over a
limited time interval. We had introduced the idea of a multi-step method to
extend the solution as far forward in time as possible. Here, we implement both
the frame shift and the multi-step method to produce an algorithm capable of
solving for the cosmological evolution of cold matter.
Extensive `proof of principle' tests validate the method. The algorithm
behaves satisfactorily in all these trials. The rate of convergence is
exponential in the grid size, exponential in the Lagrangian order and
polynomial in the step size.
There are three main advantages of this new technique. First, it employs a
smooth representation of all fields and the results are not limited by particle
induced shot-noise errors. Second, the numerical error for any problem can be
controlled by changing Lagrangian order and/or number of steps. In principle,
arbitrarily small errors can be achieved prior to orbit crossing. Third, the
initial data is completely generic, including cases where the initial velocity
field has a rotational component. Together, these properties make the new
technique well-suited to handle problems on quasi-linear scales where analytic
methods and/or numerical simulations fail to provide accurate answers.
Unified schemes of radio sources, which account for different types of radio AGN in terms of anisotropic radio and optical emission, together with different orientations of the ejection axis to the line of sight, have been invoked for many years. Recently, large samples of optical quasars, mainly from the Sloan Digital Sky Survey, together with large radio samples, such as FIRST, have become available. These hold the promise of providing more stringent tests of unified schemes but, compared to previous samples, lack high resolution radio maps. Nevertheless they have been used to investigate unified schemes, in some cases yielding results which appear inconsistent with such theories. Here we investigate using simulations how the selection effects to which such investigations are subject can influence the conclusions drawn. In particular, we find that the effects of limited resolution do not allow core-dominated radio sources to be fully represented in the samples, that the effects of limited sensitivity systematically exclude some classes of sources and the lack of deep radio data make it difficult to decide to what extent closely separated radio sources are associated. Nevertheless, we conclude that relativistic unified schemes are entirely compatible with the current observational data. For a sample selected from SDSS and FIRST which includes weak-cored triples we find that the equivalent width of the [OIII] emission line decreases as core-dominance increases, as expected, and also that core-dominated quasars are optically brighter than weak-cored quasars.
In this paper, we develop the analysis of a two-dimensional magnetohydrodynamical configuration for an axially symmetric and rotating plasma (embedded in a dipole like magnetic field), modeling the structure of a thin accretion disk around a compact astrophysical object. Our study investigates the global profile of the disk plasma, in order to fix the conditions for the existence of a crystalline morphology and ring sequence, as outlined by the local analysis pursued in [1, 2]. In the linear regime, when the electromagnetic back-reaction of the plasma is small enough, we show the existence of an oscillating radial behavior for the flux surface function which very closely resembles the one outlined in the local model, apart from a radial modulation of the amplitude. In the opposite limit, corresponding to a dominant back-reaction in the magnetic structure over the field of central object, we can recognize the existence of a ring-like decomposition of the disk, according to the same modulation of the magnetic flux surface, and a smoother radial decay of the disk density, with respect to the linear case. In this extreme non-linear regime, the global model seems to predict a configuration very close to that of the local analysis, but here the thermostatic pressure, crucial for the equilibrium setting, is also radially modulated. Among the conditions requested for the validity of such a global model, the confinement of the radial coordinate within a given value sensitive to the disk temperature and to the mass of the central objet, stands; however, this condition corresponds to dealing with a thin disk configuration.
We introduce a probabilistic (Bayesian) method for producing catalogs from images of crowded stellar fields. The method is capable of inferring the number of sources (N) in the image and can also handle the challenges introduced by overlapping sources. The luminosity function of the stars can also be inferred even when the precise luminosity of each star is uncertain. This is in contrast with standard techniques which produce a single catalog, potentially underestimating the uncertainties in any study of the stellar population and discarding information about sources at or below the detection limit. The method is implemented using advanced Markov Chain Monte Carlo (MCMC) techniques including Reversible Jump and Nested Sampling. The computational feasibility of the method is demonstrated on simulated data where the luminosity function of the stars is a broken power-law. The parameters of the luminosity function can be recovered with moderate uncertainties. We compare the results obtained from our method with those obtained from the SExtractor software and find that the latter significantly underestimates the number of stars in the image and leads to incorrect inferences about the luminosity function of the stars.
The Galactic orbital parameters of 159 cataclysmic variables in the Solar neighbourhood are calculated, for the first time, to determine their population types using published kinematical parameters. Population analysis shows that about 6 per cent of cataclysmic variables in the sample are members of the thick disc component of the Galaxy. This value is consistent with the fraction obtained from star count analysis. The rest of the systems in the sample are found to be in the thin disc component of the Galaxy. Our analysis revealed no halo CVs in the Solar vicinity. About 60 per cent of the thick disc CVs have orbital periods below the orbital period gap. This result is roughly consistent with the predictions of population synthesis models developed for cataclysmic variables. A kinematical age of 13 Gyr is obtained using total space velocity dispersion of the most probable thick disc CVs which is consistent with the age of thick disc component of the Galaxy.
We analyze the quantum-mechanical rotational excitation/de-excitation spectrum and cross sections of CN molecules during low and high-energy collisions with protons, H+. The problem is of significant importance in astrophysics of the early Universe, specifically connected with the problems of cosmic microwave background (CMB) radiation. A quantum-mechanical close-coupling method is applied in this work. The cyanide molecule (CN) is treated as a rigid rotor, i.e. the distance between the carbon and nitrogen atoms is fixed at an average equilibrium value. The new results of the excitation/de-excitation cross-sections and corresponding thermal rate coefficients are compared with the results of few previous calculations performed on the basis of few approximate semiclassical frameworks. The interaction potential between CN and H+ is taken in the following form: proton induced polarization potential + proton-dipole potential + proton-quadrupole potential.
We present the results of a new spectroscopic study of Fe K-band absorption in Active Galactic Nuclei (AGN). Using data obtained from the Suzaku public archive we have performed a statistically driven blind search for Fe XXV Hea and/or Fe XXVI Lyb absorption lines in a large sample of 51 type 1.0-1.9 AGN. Through extensive Monte Carlo simulations we find statistically significant absorption is detected at E>6.7 keV in 20/51 sources at the P(MC)>95% level, which corresponds to ~40% of the total sample. In all cases, individual absorption lines are detected independently and simultaneously amongst the two (or three) available XIS detectors which confirms the robustness of the line detections. The most frequently observed outflow phenomenology consists of two discrete absorption troughs corresponding to Fe XXV Hea and Fe XXVI Lyb at a common velocity shift. From xstar fitting the mean column density and ionisation parameter for the Fe K absorption components are log(NH/cm^{-2})~23 and log(xi/erg cm s^{-1})~4.5, respectively. Measured outflow velocities span a continuous range from <1,500 km/s up to ~100,000 km/s, with mean and median values of ~0.1c and ~0.056c, respectively. The results of this work are consistent with those recently obtained using XMM-Newton and independently provides strong evidence for the existence of very highly-ionised circumnuclear material in a significant fraction of both radio-quiet and radio-loud AGN in the local universe.
Westerlund 1 is the most important starburst cluster in the Galaxy due to its massive star content. We have performed BVIc and JKs photometry to investigate the initial mass function (IMF). By comparing the observed color with the spectral type - intrinsic color relation, we obtain the mean interstellar reddening of <E(B-V)>=4.19+/-0.23 and <E(J-Ks)>=1.70+/-0.21. Due to the heavy extinction toward the cluster, the zero-age main sequence fitting method based on optical photometry proved to be inappropriate for the distance determination, while the near-infrared photometry gave a reliable distance to the cluster -- 3.8 kpc from the empirical relation. Using the recent theoretical stellar evolution models with rotation, the age of the cluster is estimated to be 5.0+/-1.0 Myr. We derived the IMF in the massive part and obtained a fairly shallow slope of {\Gamma} = -0.8 +/- 0.1. The integration of the IMF gave a total mass for the cluster in excess of 5.0 x 10^4 solar mass. The IMF shows a clear radial variation indicating the presence of mass segregation. We also discuss the possible star formation history of Westerlund 1 from the presence of red supergiants and relatively low-luminosity yellow hypergiants.
Radio emissions from young supernovae (~ 1 year after the explosion) show a peculiar feature in the relativistic electron population at a shock wave, where their energy distribution is steeper than typically found in supernova remnants (SNRs) and than the prediction from the standard diffusive shock acceleration (DSA) mechanism. This is especially established for a class of stripped envelope supernovae (SNe IIb/Ib/Ic) where a combination of high shock velocity and low circumstellar material (CSM) density makes it easier to derive the intrinsic energy distribution than in other classes of SNe. We suggest that this apparent discrepancy reflects the situation that the low energy electrons before accelerated by the DSA-like mechanism are responsible for the radio synchrotron emission from young SNe, and that studying young SNe sheds light on the still-unresolved electron injection problem in the acceleration theory of cosmic rays. We suggest that electron's energy distribution could be flattened toward the high energy, most likely around 100 MeV, which marks a transition from inefficient to efficient acceleration. Identifying this feature will be a major advance in understanding the electron acceleration mechanism. We suggest two further probes: (1) mm/sub-mm observations in the first year after the explosion, and (2) X-ray observations at about 1 year and thereafter. We show that these are reachable by ALMA and Chandra for nearby SNe.
The Planck satellite was launched in 2009 by the European Space Agency to study the properties of the cosmic microwave background (CMB). An expected result of the Planck data analysis is the distinction of the various contaminants of the CMB signal. Among these contaminants is the Sunyaev-Zel'dovich (SZ) effect, which is caused by the inverse Compton scattering of CMB photons by high energy electrons in the intracluster medium of galaxy clusters. We modify a public version of the JADE (Joint Approximate Diagonalization of Eigenmatrices) algorithm, to deal with noisy data, and then use this algorithm as a tool to search for SZ clusters in two simulated datasets. The first dataset is composed of simple "homemade" simulations and the second of full sky simulations of high angular resolution, available at the LAMBDA (Legacy Archive for Microwave Background Data Analysis) website. The process of component separation can be summarized in four main steps: (1) pre-processing based on wavelet analysis, which performs an initial cleaning (denoising) of data to minimize the noise level; (2) the separation of the components by JADE; (3) the calibration of the recovered SZ map; and (4) the identification of the positions and intensities of the clusters using the SExtractor software. The results show that our JADE-based algorithm is effective in identifying the position and intensity of the SZ clusters, with the purities being higher then 90% for the extracted "catalogues". This value changes slightly according to the characteristics of noise and the number of components included in the input maps. The main highlight of our developed work is the effective recovery rate of SZ sources from noisy data, with no a priori assumptions. This powerful algorithm can be easily implemented and become an interesting complementary option to the "matched filter" algorithm widely used in SZ data analysis.
We show, using global 3D grid-based hydrodynamical simulations, that Ultra Fast Outflows (UFOs) from Active Galactic Nuclei (AGN) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous hot hydrostatic medium. The outflow floods through the inter-cloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically, rather than in a disc. In the latter case the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGN, they are likely to be important in the cosmological feedback cycles of galaxy formation.
Massive stars at redshifts z > 6 are predicted to have played a pivotal role in cosmological reionization as luminous sources of ultra-violet (UV) photons. However, the remnants of these massive stars could be equally important as X-ray luminous (L_X 1e38 erg/s) high-mass X-ray binaries (HMXBs). Because the absorption cross section of neutral hydrogen decreases sharply with photon energy (proportional to the inverse cube), X-rays can escape more freely than UV photons from the star-forming regions in which they are produced, allowing HMXBs to make a potentially significant contribution to the ionizing X-ray background during reionization. In this paper, we explore the ionizing power of HMXBs at redshifts z > 6 using a Monte Carlo model for a coeval stellar population of main sequence stars and HMXBs. Using the archetypal Galactic HMXB Cygnus X-1 as our template, we propose a composite HMXB spectral energy distribution consisting of black-body and power-law components, whose contributions depend on the accretion state of the system. We determine the time-dependent ionizing power of a combined population of UV-luminous stars and X-ray luminous HMXBs, and deduce fitting formulae for the boost in the population's ionizing power arising from HMXBs; these fits allow for simple implementation of HMXB feedback in numerical simulations. Based on this analysis, we estimate the contribution of high redshift HMXBs to the present-day soft X-ray background, and we show that it is a factor of ~100-1000 smaller than the observed limit. Finally, we discuss the implications of our results for the role of HMXBs in reionization and in high redshift galaxy formation.
We present two new mechanisms for neutirno-induced production of 9Be in core-collapse supernovae. In both cases, neutrino reactions in He shells produce 3H, which then makes 7Li through 4He(3H,gamma)7Li. For progenitors of ~8 M_sun, the shocked He-shell material rapidly expands, allowing production of 9Be through 7Li(3H,n_0)9Be. For ultra-metal-poor progenitors of ~11-15 M_sun, neutrons generated by neutrino reactions in He shells lead to both 7Li(n,gamma)8Li(n,gamma)9Li and a rapid neutron-capture process, depending on details of neutrino spectra, flavor oscillations, and the explosion. We discuss the associated production of 7Li and 11B, related mechanisms for 9Be production that might operate in other sites, and consistency of the identified mechanisms with the observational data.
Signals from radio pulsars show a wavelength-dependent delay due to dispersion in the interstellar plasma. At a typical observing wavelength, this delay can vary by tens of microseconds on five-year time scales, far in excess of signals of interest to pulsar timing arrays, such as that induced by a gravitational-wave background. Measurement of these delay variations is not only crucial for the detection of such signals, but also provides an unparallelled measurement of the turbulent interstellar plasma at au scales. In this paper we demonstrate that without consideration of wavelength- independent red-noise, 'simple' algorithms to correct for interstellar dispersion can attenuate signals of interest to pulsar timing arrays. We present a robust method for this correction, which we validate through simulations, and apply it to observations from the Parkes Pulsar Timing Array. Correction for dispersion variations comes at a cost of increased band-limited white noise. We discuss scheduling to minimise this additional noise, and factors, such as scintillation, that can exacerbate the problem. Comparison with scintillation measurements confirms previous results that the spectral exponent of electron density variations in the interstellar medium often appears steeper than expected. We also find a discrete change in dispersion measure of PSR J1603-7202 of ~2x10^{-3} cm^{-3}pc for about 250 days. We speculate that this has a similar origin to the 'extreme scattering events' seen in other sources. In addition, we find that four pulsars show a wavelength-dependent annual variation, indicating a persistent gradient of electron density on an au spatial scale, which has not been reported previously.
The delayed-detonation explosion mechanism applied to a Chandrasekhar-mass white dwarf offers a very attractive model to explain the inferred characteristics of Type Ia supernovae (SNe Ia). The resulting ejecta are chemically stratified, have the same mass and roughly the same asymptotic kinetic energy, but exhibit a range in 56Ni mass. We investigate the contemporaneous photometric and spectroscopic properties of a sequence of delayed-detonation models, characterized by 56Ni masses between 0.18 and 0.81 Msun. Starting at 1d after explosion, we perform the full non-LTE, time-dependent radiative transfer with the code CMFGEN, with an accurate treatment of line blanketing, and compare our results to SNe Ia at bolometric maximum. Despite the 1D treatment, our approach delivers an excellent agreement to observations. We recover the range of SN Ia luminosities, colours, and spectral characteristics from the near-UV to 1 micron, for standard as well as low-luminosity 91bg-like SNe Ia. Our models predict an increase in rise time to peak with increasing 56Ni mass, from ~15 to ~21d, yield peak bolometric luminosities that match Arnett's rule to within 10%, and reproduce the much smaller scatter in near-IR magnitudes compared to the optical. We reproduce the morphology of individual spectral features, the stiff dependence of the R(Si) spectroscopic ratio on 56Ni mass, and the onset of blanketing from TiII/ScII in low-luminosity SNe Ia with a 56Ni mass <0.3 Msun. We find that ionization effects, which often dominate over abundance variations, can produce high-velocity features in CaII lines, even in 1D. Distinguishing between different SN Ia explosion mechanisms is a considerable challenge but the results presented here provide additional support to the viability of the delayed-detonation model.
We report on a concerted effort aimed at understanding the nucleosynthesis origin of Xe-H in presolar nanodiamonds. Previously explored possible explanations have included a secondary neutron-burst process occurring in the He-shell of a type II supernova (SN), as well as a rapid separation, between unstable precursor isobars of a primary r-process, and stable Xe isotopes. Here we present results from the investigation of a rapid neutron-capture scenario in core-collapse SNe with different non-standard r-process variants. Our calculations are performed in the framework of the high-entropy-wind (HEW) scenario using updated nuclear-physics input. We explore the consequences of varying the wind expansion velocity (Vexp) for selected electron fractions (Ye) with their correlated entropy ranges (S), and neutron-freezeout temperatures (T9(freeze)) and timescales (tau-r(freeze). We draw several conclusions: For Xe-H a "cold" r-process with a fast freezeout seems to be the favored scenario. Furthermore, eliminating the low-S range (i.e. the "weak" r-process component) and maintaining a pure "main" or even "strong" r-process leads to an optimum overall agreement with the measured iXe/136Xe abundance ratios. Our results can provide valuable additional insight into overall astrophysical conditions of producing the r-process part of the total SS heavy elements in explosive nucleosynthesis scenarios.
Type I X-ray bursts are thermonuclear explosions that occur in the envelopes of accreting neutron stars. Detailed observations of these phenomena have prompted numerous studies in theoretical astrophysics and experimental nuclear physics since their discovery over 35 years ago. In this review, we begin by discussing key observational features of these phenomena that may be sensitive to the particular patterns of nucleosynthesis from the associated thermonuclear burning. We then summarize efforts to model type I X-ray bursts, with emphasis on determining the nuclear physics processes involved throughout these bursts. We discuss and evaluate limitations in the models, particularly with regard to key uncertainties in the nuclear physics input. Finally, we examine recent, relevant experimental measurements and outline future prospects to improve our understanding of these unique environments from observational, theoretical and experimental perspectives.
We use a global pixel based estimator to identify the axis of the residual Maximum Temperature Asymmetry (MTA) (after the dipole subtraction) of the WMAP 7 year Internal Linear Combination (ILC) CMB temperature sky map. The estimator is based on considering the temperature differences between opposite pixels in the sky at various angular resolutions (4 degrees-15 degrees and selecting the axis that maximizes this difference. We consider three large scale Healpix resolutions (N_{side}=16 (3.7 degrees), N_{side}=8 (7.3 degrees) and N_{side}=4 (14.7 degrees)). We compare the direction and magnitude of this asymmetry with three other cosmic asymmetry axes (\alpha dipole, Dark Energy Dipole and Dark Flow) and find that the four asymmetry axes are abnormally close to each other. We compare the observed MTA axis with the corresponding MTA axes of 10^4 Gaussian isotropic simulated ILC maps (based on LCDM). The fraction of simulated ILC maps that reproduces the observed magnitude of the MTA asymmetry and alignment with the observed \alpha dipole is in the range of 0.1%-0.5%$ (depending on the resolution chosen for the CMB map). The corresponding magnitude+alignment probabilities with the other two asymmetry axes (Dark Energy Dipole and Dark Flow) are at the level of about 1%. We propose Extended Topological Quintessence as a physical model qualitatively consistent with this coincidence of directions.
We report the discovery of a bow-shock-producing star in the vicinity of the young massive star cluster NGC 3603 using archival data of the Spitzer Space Telescope. Follow-up optical spectroscopy of this star with Gemini-South led to its classification as O6 V. The orientation of the bow shock and the distance to the star (based on its spectral type) suggest that the star was expelled from the cluster, while the young age of the cluster (~2 Myr) implies that the ejection was caused by a dynamical few-body encounter in the cluster's core. The relative position on the sky of the O6 V star and a recently discovered O2 If*/WN6 star (located on the opposite side of NGC 3603) allows us to propose that both objects were ejected from the cluster via the same dynamical event -- a three-body encounter between a single (O6 V) star and a massive binary (now the O2 If*/WN6 star). If our proposal is correct, then one can "weigh" the O2 If*/WN6 star using the conservation of the linear momentum. Given a mass of the O6 V star of 30 Msun, we found that at the moment of ejection the mass of the O2 If*/WN6 star was 175 Msun. Moreover, the observed X-ray luminosity of the O2 If*/WN6 star (typical of a single star) suggests that the components of this originally binary system have merged (e.g., because of encounter hardening).
Binary properties are usually expressed (for good observational reasons) as a function of primary mass. It has been found that the distribution of companion masses -- the mass ratio distribution -- is different for different primary masses. We argue that system mass is the more fundamental physical parameter to use. We show that if system masses are drawn from a log-normal mass function, then the different observed mass ratio distributions as a function of primary mass, from M-dwarfs to A-stars, are all consistent with a universal, flat, system mass ratio distribution. We also show that the brown dwarf mass ratio distribution is not drawn from the same flat distribution, suggesting that the process which decides upon mass ratios is very different in brown dwarfs and stars.
We analyse the evolution of coronal plasma upflows from the edges of AR 10978, which has the best limb-to-limb data coverage with Hinode's EUV Imaging Spectrometer (EIS). We find that the observed evolution is largely due to the solar rotation progressively changing the viewpoint of nearly stationary flows. From the systematic changes in the upflow regions as a function of distance from disc centre, we deduce their 3D geometrical properties as inclination and angular spread in three coronal lines (SiVII, FeXII, FeXV). In agreement with magnetic extrapolations, we find that the flows are thin, fan-like structures rooted in quasi separatrix layers (QSLs). The fans are tilted away from the AR centre. The highest plasma velocities in these three spectral lines have similar magnitudes and their heights increase with temperature. The spatial location and extent of the upflow regions in the SiVII, FeXII and FeXV lines are different owing to (i) temperature stratification and (ii) line of sight integration of the spectral profiles with significantly different backgrounds. We conclude that we sample the same flows at different temperatures. Further, we find that the evolution of line widths during the disc passage is compatible with a broad range of velocities in the flows. Everything considered, our results are compatible with the AR upflows originating from reconnections along QSLs between over-pressure AR loops and neighboring under-pressure loops. The flows are driven along magnetic field lines by a pressure gradient in a stratified atmosphere. We propose that, at any given time, we observe the superposition of flows created by successive reconnections, leading to a broad velocity distribution.
We study the prospects for measuring the dark matter distribution of voids with stacked weak lensing. We select voids from a large set of N-body simulations, and explore their lensing signals with the full ray-tracing simulations including the effect of the large-scale structure along the line-of-sight. The lensing signals are compared with simple void model predictions to reconstruct the three-dimensional mass distribution of voids. We show that the stacked weak lensing signals are detected at significant level (S/N \geq 5) for a 5000 degree^2 survey area, for a wide range of void radii up to \sim 50 Mpc. The error from the shape noise little affects lensing signals at large scale. It is also found that dense ridges around voids have a great impact on the weak lensing signals, suggesting that proper modeling of the void density profile including surrounding ridges is essential for extracting the average total mass of voids.
A nearby friable cloud in Ursa Majoris contains 270 galaxies with radial velocities 500 < VLG < 1500 km s^-1 inside the area of RA= [11h; 13h] and DEC= [+40deg; +60deg]. At present, 97 galaxies of them have individual distance estimates. We use these data to clarify the structure and kinematics of the UMa complex. According to Makarov & Karachentsev (2011), most of the UMa galaxies belong to seven bound groups, which have the following median parameters: velocity dispersion of 58 km s^-1, harmonic projected radius of 300 kpc, virial mass of 2.10^12 Msol, and virial- mass-to-K-band-luminosity of 27Msol=Lsol. Almost a half of the UMa cloud population are gas-rich dwarfs (Ir, Im, BCD) with active star formation seen in the GALEX UV-survey. The UMa groups reside within 15-19 Mpc from us, being just at the same distance as Virgo cluster. The total virial mass of the UMa groups is 4.10^13 Msol, yielding the average density of dark matter in the UMa cloud to be Omega_m = 0.08, i.e. a factor three lower than the cosmic average. This is despite the fact that the UMa cloud resides in a region of the Universe that is an apparent overdensity. A possible explanation for this is that most mass in the Universe lies in the empty space between clusters. Herewith, the mean distances and velocities of the UMa groups follow nearly undisturbed Hubble ow without a sign of the 'Z-wave" effect caused by infall toward a massive attractor. This constrains the total amount of dark matter between the UMa groups within the cloud volume.
The planned Cherenkov Telescope Array (CTA) is a future observatory for very-high-energy (VHE) gamma-ray astronomy composed of one site per hemisphere. It aims at 10 times better sensitivity, a better angular resolution and wider energy coverage than current installations such as H.E.S.S., MAGIC and VERITAS. In order to achieve this level of performance, both the design of the telescopes and the analysis algorithms are being studied and optimized within the CTA Monte-Carlo working group. Here, we present ongoing work on the data analysis for both the event reconstruction (energy, direction) and gamma/hadron separation, carried out within the HAP (H.E.S.S. Analysis Package) software framework of the H.E.S.S. collaboration, for this initial study. The event reconstruction uses both Hillas-parameter-based algorithms and an improved version of the 3D-Model algorithm. For the gamma/hadron discrimination, original and robust discriminant variables are used and treated with Boosted Decision Trees (BDTs) in the TMVA (Toolkit for Multivariate Data Analysis) framework. With this advanced analysis, known as Paris-MVA, the sensitivity is improved by a factor of about 2 in the core range of CTA relative to the standard analyses. Here we present the algorithms used for the reconstruction and discrimination, together with the resulting performance characteristics, with good confidence, since the method has been successfully applied for H.E.S.S.
White dwarfs correspond to the final stages of stellar evolution of solar-type stars. In these objects, production of energy by nuclear burning has ended which means that a white dwarf simply cools down over the course of the next billion years. It is now known that white dwarfs spend some of their cooling history in an instability strip. The pulsating white dwarfs with an hydrogen atmosphere (called DAV or ZZ Ceti stars) show non-radial oscillation modes with periods in the range 100 - 1200s. In this work we try to illustrate how the oscillation p-mode frequencies of idealized white dwarf models change as the result of a different chemical composition in the core, with the ultimate goal of determining the chemical stratification from seismic observations. The presence of acoustic glitches in the internal structure results in a periodic signal in the frequencies. We find that this signal depends on the chemical stratification/composition of the core in a form that can be analytically modelled.
Small cyclic variations in the frequencies of acoustic modes are expected to be a common phenomenon in solar-like pulsators, as a result of stellar magnetic activity cycles. The frequency variations observed throughout the solar and stellar cycles contain information about structural changes that take place inside the stars as well as about variations in magnetic field structure and intensity. The task of inferring and disentangling that information is, however, not a trivial one. In the sun and solar-like pulsators, the direct effect of the magnetic field on the oscillations might be significantly important in regions of strong magnetic field (such as solar- / stellar-spots), where the Lorentz force can be comparable to the gas-pressure gradient. Our aim is to determine the sun- / stellar-spots effect on the oscillation frequencies and attempt to understand if this effect contributes strongly to the frequency changes observed along the magnetic cycle. The total contribution of the spots to the frequency shifts results from a combination of direct and indirect effects of the magnetic field on the oscillations. In this first work we considered only the indirect effect associated with changes in the stratification within the starspot. Based on the solution of the wave equation and the variational principle we estimated the impact of these stratification changes on the oscillation frequencies of global modes in the sun and found that the induced frequency shifts are about two orders of magnitude smaller than the frequency shifts observed over the solar cycle.
To demonstrate the effect of turbulent background density fluctuations on flare accelerated electron transport in the solar corona. Using the quasi-linear approximation, we numerically simulate the propagation of a beam of accelerated electrons from the solar corona to chromosphere, including the self-consistent response of the inhomogeneous background plasma in the form of Langmuir waves. We calculate the X-ray spectrum from these simulations using the bremsstrahlung cross-section and fit the footpoint spectrum using the collisional "thick-target" model, a standard approach adopted in observational studies. We find that the interaction of the Langmuir waves with the background electron density gradient shifts the waves to higher phase velocity where they then resonate with higher velocity electrons. The consequence is that some of the electrons are shifted to higher energies, producing more high energy X-rays than expected in the cases where the density inhomogeneity is not considered. We find that the level of energy gain is strongly dependent on the initial electron beam density at higher energy and the magnitude of the density gradient in the background plasma. The most significant gains are for steep (soft) spectra which had few electrons initially at higher energies. If the X-ray spectrum of the simulated footpoint emission are fitted using the standard "thick-target" model some simulation scenarios produce more than an order-of-magnitude over estimate of the number of electrons $>50$keV in the source coronal distribution.
We report the discovery of a transiting planet with an orbital period of 1.36d orbiting the brighter component of the visual binary star BD -07 436. The host star, WASP-77A, is a moderately bright G8V star (V=10.3) with a metallicity close to solar ([Fe/H]= 0.0 +- 0.1). The companion star, WASP-77B, is a K-dwarf approximately 2 magnitudes fainter at a separation of approximately 3arcsec. The spectrum of WASP-77A shows emission in the cores of the Ca II H and K lines indicative of moderate chromospheric activity. The WASP lightcurves show photometric variability with a period of 15.3 days and an amplitude of about 0.3% that is probably due to the magnetic activity of the host star. We use an analysis of the combined photometric and spectroscopic data to derive the mass and radius of the planet (1.76+-0.06MJup, 1.21+-0.02RJup). The age of WASP-77A estimated from its rotation rate (~1 Gyr) agrees with the age estimated in a similar way for WASP-77B (~0.6 Gyr) but is in poor agreement with the age inferred by comparing its effective temperature and density to stellar models (~8 Gyr). Follow-up observations of WASP-77 Ab will make a useful contribution to our understanding of the influence of binarity and host star activity on the properties of hot Jupiters.
We show how to include in the existing calculations the corrections to the isovector coupling arising in chiral effective field theory recently found in Ref. Menendez. The dominant effect can be taken into account by conveniently redefining the static spin matrix elements $<\mathbf{S}_{p,n}>$: the largest one is reduced, on average, a 10%. To show the impact of these corrections we recalculate the limits on the WIMP-proton spin dependent cross scetion set by COUPP. We also give practical formulas to obtain $<\mathbf{S}_{p,n}>$ given the structure functions in the various formalisms/notations existing in literature. We argue that the standard treatment of the spin-dependent cross section in terms of three independent isospin functions, $S_{00}(q)$, $S_{11}(q)$, $S_{01}(q)$, is redundant in the sense that the interference function $S_{01}(q)$ is the double product $|S_{01}(q)|=2\sqrt{S_{00}(q)}\sqrt{S_{11}(q)}$.
Optical and infrared interferometers definitively established that the photometric standard Vega (alpha Lyrae) is a rapidly rotating star viewed nearly pole-on. Recent independent spectroscopic analyses could not reconcile the inferred inclination angle with the observed line profiles, preferring a larger inclination. In order to resolve this controversy, we observed Vega using the six-beam Michigan Infrared Combiner on the Center for High Angular Resolution Astronomy Array. With our greater angular resolution and dense (u,v)-coverage, we find Vega is rotating less rapidly and with a smaller gravity darkening coefficient than previous interferometric results. Our models are compatible with low photospheric macroturbulence and also consistent with the possible rotational period of ~0.71 days recently reported based on magnetic field observations. Our updated evolutionary analysis explicitly incorporates rapid rotation, finding Vega to have a mass of 2.15+0.10_-0.15 Msun and an age 700-75+150 Myrs, substantially older than previous estimates with errors dominated by lingering metallicity uncertainties (Z=0.006+0.003-0.002).
The Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) are some of the most interesting groups of pulsars that have been intensively studied in the recent years. They are seen usually as neutron stars with super strong magnetic fields, namely $B\gtrsim10^{14}$ G. However, in the last two years two SGRs with low magnetic fields $B\sim(10^{12}-10^{13})$ G have been detected. Moreover, fast and very magnetic WD pulsars have also been observed in the last years. Based on these new pulsar discoveries, white dwarf pulsars have been proposed as an alternative explanation to the observational features of SGRs and AXPs. The pulsar magnetic dipole moment depending only on the momentum of inertia $I$, and the observational properties as the period $P$ and its first time derivative $\dot{P}$, can help to identify the scale of $I$ for SGRs/AXPs. We discuss here the pulsar magnetic dipole moment $m$ of SGRs and AXPs when a model based on a massive fast rotating highly magnetized white dwarf is considered. We show that the values for $m$ obtained for almost all SGRs and AXPs are in agreement with the observed range $10^{34}{\rm emu}\leq m \leq10^{36}{\rm emu}$ of isolated and polar magnetic white dwarfs, excepted for the two SGRs with low $B$ and the AE Aquarii white dwarf pulsar where $m \simeq10^{33}$ emu. This supports the understanding of SGRs and AXPs as belonging to a class of very fast and magnetic massive white dwarfs, perfect in line to the recent astronomical observations of fast white dwarf pulsars.
Until recently, symbiotic binary systems in which a white dwarf accretes from a red giant were thought to be mainly a soft X-ray population. Here we describe the detection with the X-ray Telescope (XRT) on the Swift satellite of 10 white dwarf symbiotics that were not previously known to be X-ray sources and one that was previously detected as a supersoft X-ray source. The 10 new X-ray detections were the result of a survey of 41 symbiotic stars, and they increase the number of symbiotic stars known to be X-ray sources by 30%. Swift/XRT detected all of the new X-ray sources at energies greater than 2 keV. Their X-ray spectra are consistent with thermal emission and fall naturally into three distinct groups. The first group contains those sources with a single, highly absorbed hard component, which we identify as probably coming from an accretion-disk boundary layer. The second group is composed of those sources with a single, soft X-ray spectral component, which likely arises in a region where the winds from the two stars collide. The third group consists of those sources with both hard and soft X-ray spectral components. We also find that unlike in the optical, where rapid, stochastic brightness variations from the accretion disk are typically not seen, detectable UV flickering is a common property of symbiotic stars. Supporting our physical interpretation of the two X-ray spectral components, simultaneous Swift UV photometry shows that symbiotic stars with harder X-ray emission tend to have stronger UV flickering, which is usually associated with accretion through a disk.
Through the McDonald Observatory M Dwarf Planet Search, we have acquired nearly 3,000 high-resolution spectra of 93 late-type (K5-M5) stars over more than a decade using HET/HRS. This sample provides a unique opportunity to investigate the occurrence of long-term stellar activity cycles for low-mass stars. In this paper, we examine the stellar activity of our targets as reflected in the H-alpha feature. We have identified periodic signals for 6 stars, with periods ranging from days to more than 10 years, and find long-term trends for 7 others. Stellar cycles with P > 1 year are present for at least 5% of our targets. Additionally, we present an analysis of the time-averaged activity levels of our sample, and search for correlations with other stellar properties. In particular, we find that more massive, earlier type (M0-M2) stars tend to be more active than later type dwarfs. Furthermore, high-metallicity stars tend to be more active at a given stellar mass. We also evaluate H-alpha variability as a tracer of activity-induced radial velocity (RV) variation. For the M dwarf GJ 1170, H-alpha variation reveals stellar activity patterns matching those seen in the RVs, mimicking the signal of a giant planet, and we find evidence that the previously identified stellar activity cycle of GJ 581 may be responsible for the recently retracted planet f (Vogt et al. 2012) in that system. In general, though, we find that H-alpha is not frequently correlated with RV at the precision (typically 6-7 m/s) of our measurements.
The Bose-Einstein (BE) condensates of weakly interacting bosons in a strong gravity field, such as AGN (Active Galactic Nuclei), BHs (black holes) and neutron stars, are discussed. Being bound systems in gravity fields, these are stable reservoirs for the Higgs bosons, and vector bosons of Z and W as well as supersymmetric bosons. Upon gravitational disturbances, such as a gravitational collapse, these objects are relieved from the BE condensate bound states and decay or interact with each other freely. Using the repulsive nature of gravity at short distances which was obtained by the present author as quantum corrections to gravity, the particles produced by the decays or interactions of the bosons liberated from BE condensates can be emitted outside the horizon for our observation. It is suggested that the recently observed gamma ray peak at 129.8 +- 2.4 GeV from FERMI Large Area Telescope may be evidence for the existence of the Higgs boson condensates. The BE condensates of supersymmetric bosons are the most likely sources for the gamma rays from DMP (dark matter particle) and anti-DMP collisions. It is shown that the said process from DMPs spread in the galaxy is too small for the incident DMP with the intensity of the cosmic ray energy spectrum.
Particle production at the end of a first-order electroweak phase transition may be rather generic in theories beyond the standard model. Dark matter may then be abundantly produced by this mechanism if it has a sizable coupling to the Higgs field. For an electroweak phase transition occuring at a temperature T_EW ~ 50-100 GeV, non-thermally generated dark matter with mass M_X > TeV will survive thermalization after the phase transition, and could then potentially account for the observed dark matter relic density in scenarios where a thermal dark matter component is either too small or absent. Dark matter in these scenarios could then either be multi-TeV WIMPs whose relic abundace is mostly generated at the electroweak phase transition, or "Baby-Zillas" with mass M_GUT >> M_X >> v_EW that never reach thermal equilibrium in the early universe.
We study general constraints on spontaneous R-symmetry breaking models coming from the cosmological effects of the pseudo Nambu-Goldstone bosons, R-axions. They are substantially produced in the early Universe and may cause several cosmological problems. We focus on relatively long-lived R-axions and find that in a wide range of parameter space, models are severely constrained. In particular, R-axions with mass less than 1 MeV are generally ruled out for relatively high reheating temperature, $T_R>10$ GeV.
We study the cosmic no-hair in the presence of spin-2 matter, i.e. in bimetric gravity. We obtain stable de Sitter solutions with the cosmological constant in the physical sector and find an evidence that the cosmic no-hair is correct. In the presence of the other cosmological constant, there are two branches of de Sitter solutions. Under anisotropic perturbations, one of them is always stable and there is no violation of the cosmic no-hair at the linear level. The stability of the other branch depends on parameters and the cosmic no-hair can be violated in general. Remarkably, the bifurcation point of two branches exactly coincides with the Higuchi bound. It turns out that there exists a de Sitter solution for which the cosmic no-hair holds at the linear level and the effective mass for the anisotropic perturbations is above the Higuchi bound.
We compare three different statistical models for the equation of state (EOS) of stellar matter at subnuclear densities and temperatures (0.5-10 MeV) expected to occur during the collapse of massive stars and supernova explosions. The models introduce the distributions of various nuclear species in nuclear statistical equilibrium, but use somewhat different nuclear physics inputs. It is demonstrated that the basic thermodynamical quantities of stellar matter under these conditions are similar, except in the region of high densities and low temperatures. We demonstrate that mass and isotopic distributions have considerable differences related to the different assumptions of the models on properties of nuclei at these stellar conditions. Overall, the three models give similar trends, but the details reflect the uncertainties related to the modelling of medium effects, such as the temperature and density dependence of surface and bulk energies of heavy nuclei, and the nuclear shell structure effects. In order to establish a relationship between nuclear physics inputs for astrophysical calculations and the experimental data obtained from intermediate-energy nuclear reactions, we also discuss the similarities and differences of the conditions reached during supernova explosions and heavy-ion collisions.
The theory of a single massive graviton has a cutoff much below its Planck scale, because the extra modes from the graviton multiplet involve higher derivative self-interactions, controlled by a scale convoluted from the small graviton mass. On a generic background, these correct the propagator by environmental effects. The resulting effective cutoff depends on the environmental parameters and the graviton mass. Requiring the theory to be perturbative down to O(1) mm, we derive bounds on the graviton mass, corresponding to scales greater than or similar to O(1) meV for the generic case, and somewhat weaker bounds in cases of fine-tuning. In all cases the mass is required to be much too large for the theory to conform with GR at cosmological distances. Similar results are also found in quartic and quintic Galileon theory.
The nonlinear development of the strong Buneman instability and the associated fast electron heating in thin current layers with $\Omega_e/\omega_{pe} <1$ are explored. Phase mixing of the electrons in wave potential troughs and a rapid increase in temperature are observed during the saturation of the instability. We show that the motion of trapped electrons can be described using a Hamiltonian formalism in the adiabatic approximation. The process of separatrix crossing as electrons are trapped and de-trapped is irreversible and guarantees that the resulting electron energy gain is a true heating process.
The paper contains the results of wide-angle polarization camera (WAPC) measurements of the twilight sky background conducted in summer 2011 and 2012 at 55.2 degs.N, 37.5 degs.E, southwards from Moscow. The method of single scattering separation based on polarization data is suggested. The obtained components of scattering matrixes show the domination of Rayleigh scattering in the mesosphere for all observation days. It made possible to retrieve the altitude distribution of temperature in the mesosphere. The results are compared with the temperature data by TIMED/SABER and EOS Aura/MLS instruments for nearby dates and locations.
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A previously-derived photometric parallax of 10.10+-0.20 mas, d=99+-2 pc, is confirmed for Polaris by a spectroscopic parallax derived using line ratios in high dispersion spectra for the Cepheid. The resulting estimates for the mean luminosity of <Mv>=-3.07+-0.01 s.e., average effective temperature of <Teff>=6025+-1 K s.e., and intrinsic color of (<B>-<V>)o=0.56+-0.01 s.e., which match values obtained previously from the photometric parallax for a space reddening of E(B-V)=0.02+-0.01, are consistent with fundamental mode pulsation for Polaris and a first crossing of the instability strip, as also argued by its rapid rate of period increase. The systematically smaller Hipparcos parallax for Polaris appears discrepant by comparison.
We present a statistical parallax study of nearly 2,000 M subdwarfs with photometry and spectroscopy from the Sloan Digital Sky Survey. Statistical parallax analysis yields the mean absolute magnitudes, mean velocities and velocity ellipsoids for homogenous samples of stars. We selected homogeneous groups of subdwarfs based on their photometric colors and spectral appearance. We examined the color-magnitude relations of low-mass subdwarfs and quantified their dependence on the newly-refined metallicity parameter, zeta. We also developed a photometric metallicity parameter, delta(g-r), based on the g-r and r-z colors of low-mass stars and used it to select stars with similar metallicities. The kinematics of low-mass subdwarfs as a function of color and metallicity were also examined and compared to main sequence M dwarfs. We find that the SDSS subdwarfs share similar kinematics to the inner halo and thick disk. The color-magnitude relations derived in this analysis will be a powerful tool for identifying and characterizing low-mass metal-poor subdwarfs in future surveys such as GAIA and LSST, making them important and plentiful tracers of the stellar halo.
We present a probabilistic approach for inferring the parameters of the present day power-law stellar mass function (MF) of a resolved young star cluster. This technique (a) fully exploits the information content of a given dataset; (b) accounts for observational uncertainties in a straightforward way; (c) assigns meaningful uncertainties to the inferred parameters; (d) avoids the pitfalls associated with binning data; and (e) is applicable to virtually any resolved young cluster, laying the groundwork for a systematic study of the high mass stellar MF (M > 1 Msun). Using simulated clusters and Markov chain Monte Carlo sampling of the probability distribution functions, we show that estimates of the MF slope, {\alpha}, are unbiased and that the uncertainty, {\Delta}{\alpha}, depends primarily on the number of observed stars and stellar mass range they span, assuming that the uncertainties on individual masses and the completeness are well-characterized. Using idealized mock data, we compute the lower limit precision on {\alpha} and provide an analytic approximation for {\Delta}{\alpha} as a function of the observed number of stars and mass range. We find that ~ 3/4 of quoted literature uncertainties are smaller than the theoretical lower limit. By correcting these uncertainties to the theoretical lower limits, we find the literature studies yield <{\alpha}>=2.46 with a 1-{\sigma} dispersion of 0.35 dex. We verify that it is impossible for a power-law MF to obtain meaningful constraints on the upper mass limit of the IMF. We show that avoiding substantial biases in the MF slope requires: (1) including the MF as a prior when deriving individual stellar mass estimates; (2) modeling the uncertainties in the individual stellar masses; and (3) fully characterizing and then explicitly modeling the completeness for stars of a given mass. (abridged)
We examine the nonlinear development of unstable magnetosonic waves driven by a background radiative flux -- the Radiation-Driven Magneto-Acoustic Instability (RMI, a.k.a. the "photon bubble" instability). The RMI may serve as a persistent source of density, radiative flux, and magnetic field fluctuations in stably-stratified, optically-thick media. The conditions for instability are present in a variety of astrophysical environments, and do not require the radiation pressure to dominate or the magnetic field to be strong. Here we numerically study the saturation properties of the RMI, covering three orders of magnitude in the relative strength of radiation, magnetic field, and gas energies. Two-dimensional, time-dependent radiation-MHD simulations of local, stably-stratified domains are conducted with Zeus-MP in the optically-thick, highly-conducting limit. Our results confirm the theoretical expectations of Blaes and Socrates (2003) in that the RMI operates even in gas pressure-dominated environments that are weakly magnetized. The saturation amplitude is a monotonically increasing function of the ratio of radiation to gas pressure. Keeping this ratio constant, we find that the saturation amplitude peaks when the magnetic pressure is comparable to the radiation pressure. We discuss the implications of our results for the dynamics of magnetized stellar envelopes, where the RMI should act as a source of sub-photospheric perturbations.
There are many pertinent open issues in the area of star and planet formation. Large statistical samples of young stars across star-forming regions are needed to trigger a breakthrough in our understanding, but most optical studies are based on a wide variety of spectrographs and analysis methods, which introduces large biases. Here we show how graphical Bayesian networks can be employed to construct a hierarchical probabilistic model which allows pre-main sequence ages, masses, accretion rates, and extinctions to be estimated using two widely available photometric survey databases (IPHAS r/i/Halpha and 2MASS J-band magnitudes.) Because our approach does not rely on spectroscopy, it can easily be applied to homogeneously study the large number of clusters for which Gaia will yield membership lists. We explain how the analysis is carried out using the Markov Chain Monte Carlo (MCMC) method and provide Python source code. We then demonstrate its use on 587 known low-mass members of the star-forming region NGC 2264 (Cone Nebula), arriving at a median age of 3.0 Myr, an accretion fraction of 20+/-2% and a median accretion rate of 10^-8.4 Msol/yr. The Bayesian analysis formulated in this work delivers results which are in agreement with spectroscopic studies already in the literature, but achieves this with great efficiency by depending only on photometry. It is a significant step forward from previous photometric studies, because the probabilistic approach ensures that nuisance parameters, such as extinction and distance, are fully included in the analysis with a clear picture on any degeneracies.
In this contribution, I review the recent developments on the modelling of the lightcurve of tidal disruption events. Our understanding has evolved significantly from the earlier seminal results that imply a simple power-law decay of the bolometric light curve as $t^{-5/3}$. We now know that the details of the rise to the peak of the lightcurve is determined mainly by the internal structure of the disrupted star. We also have improved models for the disc thermal emission, showing that in this case the decline of the luminosity with time should be much flatter than the standard $t^{-5/3}$ law, especially in optical and UV wavelengths, while the X-ray lightcurve is generally best suited to track the bolometric one. Finally, we are just starting to explore the interesting general relativistic effects that might arise for such events, for which the tidal radius lies very close to the black hole event horizon. In particular, I describe here some possible evidences for relativistic Lense-Thirring precession from the light curve of the event Swift J1644.
Total-angular-momentum (TAM) waves provide a set of basis functions for scalar, vector, and tensor fields that can be used in place of plane waves and that reflect the rotational symmetry of the spherical sky. Here we discuss three-point correlation functions, or bispectra in harmonic space, for scalar, vector, and tensor fields in terms of TAM waves. The Wigner-Eckart theorem dictates that the expectation value, assuming statistical isotropy, of the product of three TAM waves is the product of a Clebsch-Gordan coefficient (or Wigner-3j symbol) times a function only of the total-angular-momentum quantum numbers. Here we show how this works, and we provide explicit expressions relating the bispectra for TAM waves in terms of the more commonly used Fourier-space bispectra. This formalism will be useful to simplify calculations of projections of three-dimensional bispectra onto the spherical sky.
We present a new method to achieve high-contrast images using segmented and/or on-axis telescopes. Our approach relies on using two sequential Deformable Mirrors to compensate for the large amplitude excursions in the telescope aperture due to secondary support structures and/or segment gaps. In this configuration the parameter landscape of Deformable Mirror Surfaces that yield high contrast Point Spread Functions is not linear, and non-linear methods are needed to find the true minimum in the optimization topology. We solve the highly non-linear Monge-Ampere equation that is the fundamental equation describing the physics of phase induced amplitude modulation. We determine the optimum configuration for our two sequential Deformable Mirror system and show that high-throughput and high contrast solutions can be achieved using realistic surface deformations that are accessible using existing technologies. We name this process Active Compensation of Aperture Discontinuities (ACAD). We show that for geometries similar to JWST, ACAD can attain at least 10^-7 in contrast and an order of magnitude higher for both the future Extremely Large Telescopes and on-axis architectures reminiscent of HST. We show that the converging non-linear mappings resulting from our Deformable Mirror shapes actually damp near-field diffraction artifacts in the vicinity of the discontinuities. Consequently, ACAD is a true broadband solution to the problem of high-contrast imaging with segmented and/or on-axis apertures. We finally show that once the non-linear solution is found, fine tuning with linear methods used in wavefront control can be applied to further contrast by another order of magnitude. Generally speaking, the ACAD technique can be used to significantly improve a broad class of telescope designs for a variety of problems.
I present an analysis of the deepest X-ray exposure of a radio millisecond pulsar (MSP) to date, an X-ray Multi Mirror-Newton European Photon Imaging Camera spectroscopic and timing observation of the nearest known MSP, PSR J0437--4715. The timing data clearly reveal a secondary broad X-ray pulse offset from the main pulse by $\sim$0.55 in rotational phase. In the context of a model of surface thermal emission from the hot polar caps of the neutron star, this can be plausibly explained by a magnetic dipole field that is significantly displaced from the stellar center. Such an offset, if commonplace in MSPs, has important implications for studies of the pulsar population, high energy pulsed emission, and the pulsar contribution to cosmic ray positrons. The continuum emission shows evidence for at least three thermal components, with the hottest radiation most likely originating from the hot magnetic polar caps and the cooler emission from the bulk of the surface. I present pulse phase-resolved X-ray spectroscopy of PSR J0437--4715, which for the first time, properly accounts for the system geometry of a radio pulsar. Such an approach is essential for unbiased measurements of the temperatures and emission areas of polar cap radiation from pulsars. Detailed modelling of the thermal pulses, including relativistic and atmospheric effects, provides a constraint on the redshift-corrected neutron star radius of R>11.1 km (at 3 sigma conf.) for the current radio timing mass measurement of 1.76 M_sun. This limit favors "stiff'" equations of state.
We select a sample of young passive galaxies from the Sloan Digital Sky Survey Data Release 7 in order to study the processes that quench star formation in the local universe. Quenched galaxies are identified based on the contribution of A-type stars to their observed (central) spectra and relative lack of ongoing star formation; we find that such systems account for roughly 2.5 per cent of all galaxies with log M_sun >= 9.5, and have a space density of ~2.2x10^-4 Mpc^-3. We show that quenched galaxies span a range of morphologies, but that visual classifications suggest they are predominantly early-type systems. Their visual early-type classification is supported by quantitative structural measurements Sersic indices that show a notable lack of disk-dominated galaxies, suggesting that any morphological transformation associated with galaxies' transition from star-forming to passive--e.g. the formation of a stellar bulge--occurs contemporaneously with the decline of their star-formation activity. We show that there is no clear excess of optical AGN in quenched galaxies, suggesting that: i) AGN feedback is not associated with the majority of quenched systems or ii) that the observability of quenched galaxies is such that the quenching phase in general outlives any associated nuclear activity. Comparison with classical post-starburst galaxies shows that both populations show similar signatures of bulge growth, and we suggest that the defining characteristic of post-starburst galaxies is the efficiency of their bulge growth rather than a particular formation mechanism.
We combine far-infrared photometry from Herschel (PEP/HERMES) with deep mid-infrared spectroscopy from Spitzer to investigate the nature and the mass assembly history of a sample of 31 Luminous and Ultraluminous Infrared Galaxies at z~1 and 2 selected in GOODS-S with 24 $\mu$m fluxes between 0.2 and 0.5 mJy. We model the data with a self-consistent physical model (GRASIL) which includes a state-of-the-art treatment of dust extinction and reprocessing. We find that all of our galaxies appear to require massive populations of old (>1 Gyr) stars and, at the same time, to host a moderate ongoing activity of SF (SFR < 100 M$_{\odot}$/yr). The bulk of the stars appear to have been formed a few Gyr before the observation in essentially all cases. Only five galaxies of the sample require a recent starburst superimposed on a quiescent star formation history (SFH). We also find discrepancies between our results and those based on optical-only SED fitting for the same objects; by fitting their observed Spectral Energy Distributions with our physical model we find higher extinctions (by $\Delta$A_{V} ~ 0.81 and 1.14) and higher stellar masses (by $\Delta$Log(M*) ~ 0.16 and 0.36 dex) for z~1 and z~2 (U)LIRGs, respectively. The stellar mass difference is larger for the most dust obscured objects. We also find lower SFRs than those computed from L_{IR} using the Kennicutt relation due to the significant contribution to the dust heating by intermediate-age stellar populations through 'cirrus' emission (~73% and ~66% of total L_{IR} for z~1 and z~2 (U)LIRGs, respectively).
Studying a range of old metal-poor stars provides information over cosmological timescales of our Galaxy. Such studies are indicative of the pristine gases and evolution of the Milky Way. Deriving stellar parameters and abundances from high-resolution observations of stars at various stellar evolution stages (including old dwarfs and RR Lyrae), allows us to use these abundances as tracers of an even earlier progenitor population. Here, we carry out a detailed abundance study of mainly heavy elements (Z > 38), i.e. neutron-capture elements, which we at low metallicities ([Fe/H] < -2.5) take as pure supernova type II products. A comparison of the derived abundances to type II supernova yields of heavy elements provides knowledge of the old stellar generations as well as properties of neutron-capture formation sites.
In this paper we present gas density, star formation rate, stellar masses, and bulge disk decompositions for a sample of 60 galaxies. Our sample is the combined sample of BIMA SONG, CARMA STING, and PdBI NUGA surveys. We study the effect of using CO-to-H_2 conversion factors that depend on the CO surface brightness, and also that of correcting star formation rates for diffuse emission from old stellar populations. We estimate that star formation rates in bulges are typically lower by 20% when correcting for diffuse emission. We find that over half of the galaxies in our sample have molecular gas surface density >100 M_sun pc^-2. We find a trend between gas density of bulges and bulge Sersic index; bulges with lower Sersic index have higher gas density. Those bulges with low Sersic index (pseudobulges) have gas fractions that are similar to that of disks. We also find that there is a strong correlation between bulges with the highest gas surface density and the galaxy being barred. However, we also find that classical bulges with low gas surface density can be barred as well. Our results suggest that understanding the connection between the central surface density of gas in disk galaxies and the presence of bars should also take into account the total gas content of the galaxy and/or bulge Sersic index. Indeed, we find that high bulge Sersic index is the best predictor of low gas density inside the bulge (not barredness of the disk). Finally, we show that when using the corrected star formation rates and gas densities, the correlation between star formation rate surface density and gas surface density of bulges is similar to that of disks.
The $^{14}$C production of shock-accelerated particles is calculated in terms of the total energy released in energetic particles. The recently reported 1.2% jump in the $^{14}$C content of the atmosphere in the year C.E. 775, it is found, would require $\gtrsim 10^{34}$ erg in energetic particles, less than first estimates but far more than any known solar flare on record. It is noted that the superflare from a large comet (comparable to C/Hale-Bopp) colliding with the sun could produce shock-accelerated GeV cosmic rays in the solar corona and/or solar wind, and possibly account for the CE 775 event. Several additional predictions of cometary encounters with the sun and other stars may be observable in the future.
We quantify the systematics in the size-luminosity relation of galaxies in the SDSS main sample which arise from fitting different 1- and 2-component model profiles to the images. In objects brighter than L*, fitting a single Sersic profile to what is really a two-component SerExp system leads to biases: the half-light radius is increasingly overestimated as n of the fitted single component increases; it is also overestimated at B/T ~ 0.6. However, the net effect on the R-L relation is small, except for the most luminous tail, where it curves upwards towards larger sizes. We also study how this relation depends on morphological type. Our analysis is one of the first to use Bayesian-classifier derived weights, rather than hard cuts, to define morphology. Crudely, there appear to be only two relations: one for early-types (Es, S0s and Sa's) and another for late-types (Sbs and Scds). However, closer inspection shows that within the early-type sample S0s tend to be 15% smaller than Es of the same luminosity, and, among faint late types, Sbs are more than 25% smaller than Scds. Neither the early- nor the late-type relations are pure power-laws: both show significant curvature, which we quantify. However, the R-L relations of the bulges of early-types are almost pure power laws; at fixed velocity dispersion sigma, these bulges satisfy the viral theorem scaling, having Rbulge ~ Lbulge. We also show that the intrinsic scatter around the relation decreases at large luminosity and/or stellar mass; this should provide additional constraints on models of how the most massive galaxies formed. Our analysis confirms that two mass scales are special for early-type galaxies: M* = 3e10 and 2e11 Msun. These same mass scales are also special for late types: there is almost no correlation between R and M* below the former, and almost no late-types above the latter.
We present simulations used to test the two dimensional decompositions of SDSS galaxies utilizing the fitting routine GALFIT and analysis pipeline PyMorph. Analysis showing the bias and scatter of the recovered parameters is presented for multiple combinations of simulated galaxy models and fit types. The simulations show that accurate measurement of single Sersic models is well constrained when using SDSS-quality data. Two component fits present a less robust image decomposition. Galaxies observed at higher redshift by Hubble are also simulated. We examine the bias created when fitting incorrect models to galaxies. Fitting a two-component Sersic + Exponential model to what is really just a single Sersic results in a noisier recovery of the input parameters, but these are not biased; fitting a single Sersic to what is truly a two-component system results in significant biases. These biases, for total magnitude and halflight radius in particular, should be useful in correcting other automatic fitting routines.
We investigate observational properties of a kilo-parsec scale knot in radio-loud quasar 3C 380 by using two epoch archival data obtained by Very Long Baseline Interferometry (VLBI) at 5 GHz on 1998 July and 2001 April. We succeed in obtaining the highest spatial resolution image of the bright knot K1 located at 732 milliarcseconds, or more than 20 kpc de-projected, downstream from the nucleus three times better than previously obtained highest resolution image by Papageorgiou et al. (2006). Our images reveal, with new clarity, "inverted bow-shock" structure in K1 facing the nucleus and its morphology resembles a conical shock wave. By comparing the two epoch images directly, we explore the kinematics of K1 and obtain the upper limit of apparent velocity, 0.25 mas/yr or 9.8 c of K1 for the first time. The upper limit of apparent velocity is marginally smaller than superluminal motions seen in the core region. Further new epoch VLBI observations are necessary to measure the proper motion at K1.
We use Gaussian Processes to map the expansion history of the universe in a model independent manner from the Union2.1 supernovae data and then apply these reconstructed results to solve for the growth history. By comparing this to BOSS and WiggleZ large scale structure data we examine whether growth is determined wholly by expansion, with the measured gravitational growth index testing gravity without assuming a model for dark energy. A further model independent analysis looks for redshift dependent deviations of growth from the general relativity solution without assuming the growth index form. Both approaches give results consistent with general relativity.
The hosts of luminous z~2 quasars evolve into today's massive elliptical galaxies. Current theories predict that the circum-galactic medium (CGM) of these massive, dark-matter halos (M~10^12.5 Msun) should be dominated by a T~10^7 K virialized plasma. We test this hypothesis with observations of 74 close-projected quasar pairs, using spectra of the background QSO to characterize the CGM of the foreground one. Surprisingly, our measurements reveal a cool (T~10^4 K), massive (M_CGM > 10^10 Msun), and metal-enriched (Z > ~0.1 Zsun) medium extending to at least the expected virial radius (r_vir = 160 kpc). The average equivalent widths of HI Lya (<W_lya> = 2.1 pm 0.15Ang for impact parameters R<200 kpc) and CII 1334 (<W_1334> = 0.7 pm 0.1Ang) exceed the corresponding CGM measurements of these transitions from all galaxy populations studied previously. Furthermore, we conservatively estimate that the quasar CGM has a 64% covering fraction of optically thick gas (N_HI>10^17.2) within r_vir; this covering factor is twice that of the contemporaneous Lyman Break Galaxy population. This unexpected reservoir of cool gas is rarely detected "down-the-barrel" to quasars, and hence it is likely that our background sightlines intercept gas which is shadowed from the quasar ionizing radiation by the same obscuring medium often invoked in models of AGN unification. Because the high-z halos inhabited by quasars predate modern groups and clusters, these observations are also relevant to the formation and enrichment history of the intragroup/intracluster medium.
I review the current status of studies of the X-ray sources in Galactic old open clusters. Cataclysmic variables (CVs), magnetically-active binaries (ABs), and sub-subgiants (SSGs) dominate the X-ray emission of old open clusters. Surprisingly, the number of ABs detected inside the half-mass radius with Lx >~ 1e30 erg/s (0.3-7 keV) does not appear to scale with cluster mass. Comparison of the numbers of CVs, ABs, and SSGs per unit mass in old open and globular clusters shows that each of these classes is under-abundant in globulars. This suggests that dense environments suppress the frequency of even some of the hardest binaries.
We present an eccentric, short-period brown dwarf candidate orbiting the active, slightly evolved subgiant star TYC 2087-00255-1, which has effective temperature T_eff = 5903+/-42 K, surface gravity log (g) = 4.07+/-0.16 (cgs), and metallicity [Fe/H] = -0.23+/-0.07. This candidate was discovered using data from the first two years of the Multi-object APO Radial Velocity Exoplanets Large-area Survey (MARVELS), which is part of the third phase of Sloan Digital Sky Survey. From our 38 radial velocity measurements spread over a two-year time baseline, we derive a Keplerian orbital fit with semi-amplitude K=3.571+/-0.041 km/s, period P=9.0090+/-0.0004 days, and eccentricity e=0.226+/-0.011. Adopting a mass of 1.16+/-0.11 Msun for the subgiant host star, we infer that the companion has a minimum mass of 40.0+/-2.5 M_Jup. Assuming an edge-on orbit, the semimajor axis is 0.090+/-0.003 AU. The host star is photometrically variable at the \sim1% level with a period of \sim13.16+/-0.01 days, indicating that the host star spin and companion orbit are not synchronized. Through adaptive optics imaging we also found a point source 643+/-10 mas away from TYC 2087-00255-1, which would have a mass of 0.13 Msun if it is physically associated with TYC 2087-00255-1 and has the same age. Future proper motion observation should be able to resolve if this tertiary object is physically associated with TYC 2087-00255-1 and make TYC 2087-00255-1 a triple body system. Core Ca II H and K line emission indicate that the host is chromospherically active, at a level that is consistent with the inferred spin period and measured v_{rot}*sin i, but unusual for a subgiant of this T_eff. This activity could be explained by ongoing tidal spin-up of the host star by the companion.
In the last decade Cherenkov telescopes on the ground and space-based \gamma-ray instruments have identified a new class of high mass X-ray binaries (HMXB), whose emission is dominated by \gamma rays. To date only five of these systems are known. All of them are detected by Cherenkov telescopes in the TeV energy range, while at GeV energies there is still one (HESS J0632+057) that has no reported detection with the Fermi-LAT. A deep search for \gamma-ray emission of HESS J0632+057 has been performed using more than 3.5 years of Fermi-LAT data. We discuss the results of this search and compare it to other \gamma-ray binary systems.
Symbiotic binaries are systems containing white dwarfs (WDs) and red giants. Symbiotic novae are those systems in which thermonuclear eruptions occur on the WD components. These are to be distinguished from events driven by accretion disk instabilities analogous to dwarf novae eruptions in cataclysmic variable outbursts. Another class of symbiotic systems are those in which the WD is extremely luminous and it seems likely that quiescent nuclear burning is ongoing on the accreting WD. A fundamental question is the secular evolution of the WD. Do the repeated outbursts or quiescent burning in these accreting systems cause the WD to gain or lose mass? If it is gaining mass, can it eventually reach the Chandrasekhar Limit and become a supernova (a SN Ia if it can hide the hydrogen and helium in the system)? In order to better understand these systems, we have begun a new study of the evolution of Thermonuclear Runaways (TNRs) in the accreted envelopes of WDs using a variety of initial WD masses, luminosities and mass accretion rates. We use our 1-D hydro code, NOVA, which includes the new convective algorithm of Arnett, Meakin and Young, the Hix and Thielemann nuclear reaction solver, the Iliadis reaction rate library, the Timmes equation of state, and the OPAL opacities. We assume a solar composition (Lodders abundance distribution) and do not allow any mixing of accreted material with core material. This assumption strongly influences our results. We report here (1) that the WD grows in mass for all simulations so that canonical `steady burning' does not occur, and (2) that only a small fraction of the accreted matter is ejected in some (but not all) simulations. We also find that the accreting systems, before thermonuclear runaway, are too cool to be seen in X-ray searches for SN Ia progenitors.
In this paper we present the first formulation of the theory of non-linear particle acceleration in collisionless shocks in the presence of neutral hydrogen in the acceleration region. The dynamical reaction of the accelerated particles, the magnetic field amplification and the magnetic dynamical effects on the shock are also included. The main new aspect consists however in accounting for charge exchange and ionization of neutral hydrogen, which profoundly change the structure of the shock, as discussed in our previous work. This important dynamical effect of neutrals is mainly associated to the so-called neutral return flux, namely the return of hot neutrals from the downstream region to the upstream, where they deposit energy and momentum through charge exchange and ionization. We also present the self-consistent calculation of Balmer line emission from the shock region and discuss how to use measurements of the anomalous width of the different components of the Balmer line to infer the cosmic ray acceleration efficiency in supernova remnants showing Balmer emission: the broad Balmer line, which is due to charge exchange of hydrogen atoms with hot ions downstream of the shock, is shown to become narrower as a result of the energy drainage into cosmic rays, while the narrow Balmer line, due to charge exchange in the cosmic-ray--induced precursor, is shown to become broader. In addition to these two well-known components, the neutral return flux leads to the formation of a third component with intermediate width: this too contains information on ongoing processes at the shock.
The physical modeling of the accretion disk boundary layer, the region where the disk meets the surface of the accreting star, usually relies on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear viscosity, widely adopted in astrophysics, satisfies this assumption by construction. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability is inefficient in this inner disk region. I will discuss the results of a recent study on the generation of hydromagnetic stresses and energy density in the boundary layer around a weakly magnetized star. Our findings suggest that although magnetic energy density can be significantly amplified in this region, angular momentum transport is rather inefficient. This seems consistent with the results obtained in numerical simulations and suggests that the detailed structure of turbulent MHD boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity.
The ages of globular clusters in our own Milky Way are known with precision
of about \pm 1 Gyr, hence their formation at redshifts z>~3 and their role in
hierarchical cosmology and the reionization of the intergalactic medium remain
relatively undetermined. Here we analyze the effect of globular cluster
formation on the observed rest-frame UV luminosity functions (LFs) and UV
continuum slopes of high redshift galaxies in the Hubble Ultra Deep Fields. We
find that the majority of present day globular clusters have formed during two
distinct epochs: at redshifts z ~ 2-3 and at redshifts z>~6. The birth of
proto-GC systems produce the steep, faint-end slopes of the galaxy LFs, and
because the brightness of proto-GCs fades 5 Myrs after their formation, their
blue colors are in excellent agreement with observations.
Our results suggest that: i) the bulk of the old globular cluster population
with estimated ages >~12 Gyr (about 50% of the total population), formed in the
relatively massive dwarf galaxies at redshifts z>~6; ii) proto-GC formation was
an important mode of star formation in those dwarf galaxies, and likely
dominated the reionization process. Another consequence of this scenario is
that some of the most massive Milky Way satellites may be faint and yet
undiscovered because tidal stripping of a dominant GC population precedes
significant stripping of the dark matter halos of these satellites. This
scenario may alleviate some remaining tensions between CDM simulations and
observations.
We analyze the spectra, spatial distributions and kinematics of Ha, [NII] and [SII] emission in a sample of 42, z~2.2 UV/optically selected star forming galaxies (SFGs) from the SINS & zC-SINF surveys, 35 of which were observed in the adaptive optics mode of SINFONI. This is supplemented by kinematic data from 48 z~1-2.5 galaxies from the literature. We find that the kinematic classification of the high-z SFGs as `dispersion dominated' or `rotation dominated' correlates most strongly with their intrinsic sizes. Smaller galaxies are more likely `dispersion-dominated' for two main reasons: 1) The rotation velocity scales linearly with galaxy size but intrinsic velocity dispersion does not depend on size, and as such, their ratio is systematically lower for smaller galaxies, and 2) Beam smearing strongly decreases large-scale velocity gradients and increases observed dispersion much more for galaxies with sizes at or below the resolution. Dispersion dominated SFGs may thus have intrinsic properties similar to `rotation dominated' SFGs, but are primarily more compact, lower mass, less metal enriched and may have higher gas fractions, plausibly because they represent an earlier evolutionary state.
We discuss observations of pseudostreamers and their 3D magnetic configuration as reconstructed with potential field source surface (PFSS) models to study their contribution to the solar wind. To understand the outflow from pseudostreamers the 3D expansion factor must be correctly estimated. Pseudostreamers may contain filament channels at their base in which case the open field lines diverge more strongly and the corresponding greater expansion factors lead to slower wind outflow, compared with pseudostreamers in which filament channels are absent. In the neighborhood of pseudostreamers the expansion factor does not increase monotonically with distance from the sun, and doesn't simply depend on the height of the pseudostreamer null point but on the entire magnetic field configuration.
The MMT and Magellan infrared spectrograph (MMIRS) is a cryogenic multiple slit spectrograph operating in the wavelength range 0.9-2.4 micron. MMIRS' refractive optics offer a 6.9 by 6.9 arcmin field of view for imaging with a spatial resolution of 0.2 arcsec per pixel on a HAWAII-2 array. For spectroscopy, MMIRS can be used with long slits up to 6.9 arcmin long, or with custom slit masks having slitlets distributed over a 4 by 6.9 arcmin area. A range of dispersers offer spectral resolutions of 800 to 3000. MMIRS is designed to be used at the f/5 foci of the MMT or Magellan Clay 6.5m telescopes. MMIRS was commissioned in 2009 at the MMT and has been in routine operation at the Magellan Clay Telescope since 2010. MMIRS is being used for a wide range of scientific investigations from exoplanet atmospheres to Ly-alpha emitters.
In this manuscript, we carefully check the correlation between the line width and the line flux of the double-peaked broad H$\alpha$ of the well-known mapped AGN 3C390.3, in order to show some further distinctions between double-peaked emitters and normal broad line AGN. Based on the Virialization assumption and the empirical relation about $R_{BLR}$, one strong negative correlation of line parameters of the double-peaked broad lines should be expected for 3C390.3, such as the negative correlation confirmed for the mapped broad line object NGC5548. But, based on the public spectra around 1995 from the AGNWATCH project for 3C390.3, one reliable positive correlation is found. In the context of the proposed theoretical accretion disk model for double-peaked emitters, the unexpected positive correlation can be naturally explained, due to different time delays for inner parts and outer parts of disk-like BLR of 3C390.3. Moreover, the Virialization assumption is checked and found to be still available for 3C390.3. However, time-varying size of the BLR of 3C390.3 can not be expected by the empirical relation $R_{BLR}\propto L^{\sim0.5}$, the continuum emission strengthening leads to the size of BLR decreasing (not increasing) in different moments for 3C390.3. Then, we compared our results of 3C390.3 with the previous results reported in the literature for the other double-peaked emitters, and found that before to clearly correct effects from disk physical parameters varying for long-term observed line spectra and effects from the probable 'external' ionizing source with so far unclear structures, it is hard to give one conclusion that the positive correlation can be found for all double-peaked emitters. However, once one positive correlation of broad line parameters was found, the accretion disk origination of the broad line should be firstly considered.
We report on results of astrometric observations of water vapor masers in the "water fountain" source IRAS 18286-0959 (I18286) with the VLBI Exploration of Radio Astrometry (VERA). These observations yielded an annual parallax of IRAS 18286-0959, pi=0.277+/-0.041 mas, corresponding to a heliocentric distance of D=3.61(+0.63)(-0.47) kpc. The maser feature, whose annual parallax was measured, showed the absolute proper motion of (mu_alpha, mu_delta)=(-3.2 +/- 0.3, -7.2 +/- 0.2) [mas/yr]. The intrinsic motion of the maser feature in the internal motions of the cluster of features in I18286 does not seem to trace the motion of the bipolar jet of I18286. Taking into account this intrinsic motion, the derived motion of the maser feature is roughly equal to that of the maser source I18286 itself. The proximity of I18286 to the Galactic midplane (z~10 pc) suggests that the parental star of the water fountain source in I18286 should be intermediate-mass AGB/post-AGB star, but the origin of a large deviation of the systemic source motion from that expected from the Galactic rotation curve is still unclear.
We present the HI column density distribution function,\fnh, as measured from dwarf galaxies observed as part of the Faint Irregular Galaxy GMRT (FIGGS) survey. We find that the shape of the dwarf galaxy \fnh\ is significantly different from the \fnh\ for high redshift Damped \lya\ absorbers (DLAs) or the \fnh\ for a representative sample of $z = 0$ gas rich galaxies. The dwarf \fnh\ falls much more steeply at high HI column densities as compared to the other determinations. While $\sim 10%$ of the cross section above $\nh = 10^{20.3} \acc$ at $z = 0$ is provided by dwarf galaxies, the fraction falls to $\lesssim 1%$ by $\nh \sim 10^{21.5} \acc.$ In the local universe, the contribution to the high \nh\ end of the \fnh\ distribution comes predominantly from the inclined disks of large galaxies. Dwarf galaxies, both because of their smaller scale lengths, and their larger intrinsic axial ratios do not produce large HI column densities even when viewed edge-on. If high column density DLAs/GRB hosts correspond to galaxies like the local dwarfs, this would require either that (i) the absorption arises from merging and not isolated systems or (ii) the observed lines of sight are strongly biased towards high column density regions.
Measuring the two-point correlation function of the galaxies in the Universe gives access to the underlying dark matter distribution, which is related to cosmological parameters and to the physics of the primordial Universe. The estimation of the correlation function for current galaxy surveys makes use of the Landy-Szalay estimator, which is supposed to reach minimal variance. This is only true, however for a vanishing correlation function. We study the Landy-Szalay estimator when these conditions are not fulfilled and propose a new estimator that provides the smallest variance for a given survey geometry. Our estimator is a linear combination of ratios between pair-counts of data and/or random catalogues (DD, RR and DR). The optimal combination for a given geometry is determined by using log-normal mock catalogues. The resulting estimator is biased in a model dependent way, but we propose a simple iterative procedure to obtain an unbiased model independent estimator. Using various sets of simulated data (log-normal, second-order LPT and N-Body), we obtain a 20-25% gain on the error bars on the two-point correlation function for the SDSS geometry and $\Lambda$CDM correlation function. When applied on to SDSS data (DR7 and DR9), we achieve a similar gain on the correlation functions which translates in a 10-15% improvement on the estimation of the densities of matter, $\Omega_m$, and dark energy, $\Omega_\Lambda$ in open LCDM model. The constraints derived from DR7 data with our estimator are similar to those obtained with the DR9 data and the Landy-Szalay estimator which covers a volume twice larger and with a density three times higher.
(Abridged) Estimating the uncertainty on the matter power spectrum internally (i.e. directly from the data) is made challenging by the simple fact that galaxy surveys offer at most a few independent samples. In addition, surveys have non-trivial geometries, which make the interpretation of the observations even trickier, but the uncertainty can nevertheless be worked out within the Gaussian approximation. With the recent realization that Gaussian treatments of the power spectrum lead to biased error bars about the dilation of the baryonic acoustic oscillation scale, efforts are being directed towards developing non-Gaussian analyses, mainly from N-body simulations so far. We propose in this paper a novel method that aims at measuring non-Gaussian error bars on the matter power spectrum directly from galaxy survey data. We utilize known symmetries of the 4-point function, Wiener filtering and principal component analysis to estimate the full covariance matrix from only four independent fields. We assess the quality of the estimated covariance matrix with a measurement of the Fisher information content in the amplitude of the power spectrum. With the noise filtering techniques and only four fields, we are able to recover the results obtained from a large N=200 sample to within 20 per cent, for k less or equal to 1.0 h/Mpc. We further provide error bars on Fisher information and on the best-fitting parameters, and identify which parts of the non-Gaussian features are the hardest to extract. Finally, we provide a prescription to extract a noise-filtered, non-Gaussian, covariance matrix from a handful of fields in the presence of a survey selection function.
We present a generic and fully-automatic method aimed at detecting absorption lines in the spectra of astronomical objects. The algorithm estimates the source continuum flux using a dimensionality reduction technique, nonnegative matrix factorization, and then detects and identifies metal absorption lines. We apply it to a sample of ~100,000 quasar spectra from the Sloan Digital Sky Survey and compile a sample of ~40,000 Mg II & Fe II absorber systems, spanning the redshift range 0.4< z < 2.3. The corresponding catalog is publicly available. We study the statistical properties of these absorber systems and find that the rest equivalent width distribution of strong Mg II absorbers follows an exponential distribution at all redshifts, confirming previous studies. Combining our results with recent near-infrared observations of Mg II absorbers we introduce a new parametrization that fully describes the incidence rate of these systems up to z~5. We find the redshift evolution of strong Mg II absorbers to be remarkably similar to the cosmic star formation history over 0.4<z<5.5 (the entire redshift range covered by observations), suggesting a physical link between these two quantities.
The high resolution optical spectra of H-deficient stars, R Coronae Borealis stars and H-deficient carbon stars are analyzed by synthesizing the C2 Swan bands (0,1), (0,0), and (1,0) using our detailed line-list and Uppsala model atmosphere, to determine the C-abundances and the 12C/13C ratios which are potential clues to the formation process of these stars. The C-abundances derived from C2 bands are about the same for the adopted models constructed with different carbon abundances over the range 8.5 (C/He = 0.1%) to 10.5 (C/He = 10%). The carbon abundances derived from C I lines are a factor of four lower than that adopted for the model atmosphere over the same C/He interval, as reported by Asplund et al.: 'the carbon problem'. In principle, the carbon abundances obtained from C2 Swan bands and that adopted for the model atmosphere can be equated for a particular choice of C/He that varies from star to star (unlike C I lines). Then, the carbon problem for C2 bands is eliminated. However, such C/He ratios are in general less than those of the extreme helium stars, the seemingly natural relatives to the RCB and HdC stars. The derived carbon abundances and the 12C/13C ratios are discussed in light of the double degenerate (DD) and the final flash (FF) scenarios. The carbon abundance and the 12C/13C ratios for the FF product, Sakurai's Object is derived. The carbon abundance in the Sakurai's object is 10 times higher than in the RCB star VZ Sgr. On an average, the carbon abundance in the Sakurai's Object is about 10 to 100 times higher than in RCB stars. The 12C/13C ratio in Sakurai's Object is 3.4, the equilibrium value, as expected for FF products.
The pulsating DA white dwarfs (ZZ Ceti stars) are $g$-mode non-radial pulsators. Asteroseismology provides strong constraints on their global parameters and internal structure. Since all the DA white dwarfs falling in the ZZ Ceti instability strip do pulsate, the internal structure derived from asteroseismology brings knowledge for the DA white dwarfs as a whole group. HS 0507+0434B is one of the ZZ Ceti stars which lies approximately in the middle of the instability strip for which we have undertaken a detailed asteroseismological study. We carried out multisite observation campaigns in 2007 and from December 2009 to January 2010. In total, 206 hours of photometric time-series have been collected. They have been analysed by means of Fourier analysis and simultaneous multi-frequency sine-wave fitting. In total, 39 frequency values are resolved including 6 triplets and a number of linear combinations. We identify the triplets as $\ell$=1 $g$-modes split by rotation. We derived the period spacing, the rotational splitting and the rotation rate. From the comparison of the observed periods with the theoretical periods of a series of models we estimate the fundamental parameters of the star: its total mass M$_{*}$/M$_{\odot}$ = 0.675, its luminosity L/L$_{\odot}$=3.5$\times 10^{-3}$, and its hydrogen mass fraction M$_{H}$/M$_{*}$= 10$^{-8.5}$.
The problem of interaction of the rotating magnetic field, frozen to a star, with a thin well conducting accretion disk is solved exactly. It is shown that a disk pushes the magnetic field lines towards a star, compressing the stellar dipole magnetic field. At the point of corotation, where the Keplerian rotation frequency coincides with the frequency of the stellar rotation, the loop of the electric current appears. The electric currents flow in the magnetosphere only along two particular magnetic surfaces, which connect the corotation region and the inner edge of a disk with the stellar surface. It is shown that the closed current surface encloses the magnetosphere. Rotation of a disk is stopped at some distance from the stellar surface, which is 0.55 of the corotation radius. Accretion from a disk spins up the stellar rotation. The angular momentum transferred to the star is determined.
A conducting disk significantly changes the generation of the electromagnetic radiation excited by the rotation of the magnetic field frozen to a star. Due to the reflection of waves from a disk there appear waves propagating toward a star, not only outward a star as it takes place for the magneto-dipole radiation. Because that the angular momentum can be transformed from a disk to a star when the inner edge of a disk approaches the light surface of a rotating star. This is purely electromagnetic effect. At some distance of a disk from a star, $r_d=r^*\simeq c/\omega_s$, the stellar angular momentum losses due to the electromagnetic radiation become zero. It results the stable stellar rotation.
We present the most energetic BALQSO outflow measured to date, with a kinetic luminosity of at least 10^46 ergs/s, which is 5% of the bolometric luminosity of this high Eddington ratio quasar. The associated mass flow rate is 400 solar masses per year. Such kinetic luminosity and mass flow rate should provide strong AGN feedback effects. The outflow is located at about 300 pc from the quasar and has a velocity of roughly 8000 km/s. Our distance and energetic measurements are based in large part on the identification and measurement of SIV and SIV* BALs. The use of this high ionization species allows us to generalize the result to the majority of high ionization BALQSOs that are identified by their CIV absorption. We also report the energetics of two other outflows seen in another object using the same technique. The distances of all 3 outflows from the central source (100-2000pc) suggest that we observe BAL troughs much farther away from the central source than the assumed acceleration region of these outflows (0.01-0.1pc).
An overview is given about recent developments and results of comprehensive simulations of magneto-convective processes in the near-surface layers and photosphere of the Sun. Simulations now cover a wide range of phenomena, from whole active regions, over individual sunspots and pores, magnetic flux concentrations and vortices in intergranular lanes, down to the intricate mixed-polarity structure of the magnetic field generated by small-scale dynamo action. The simulations in concert with high-resolution observations have provided breakthroughs in our understanding of the structure and dynamics of the magnetic fields in the solar photosphere.
A Large Quasar Group (LQG) of particularly large size and high membership has been identified in the DR7QSO catalogue of the Sloan Digital Sky Survey. It has characteristic size (volume^1/3) ~ 500 Mpc (proper size, present epoch), longest dimension ~ 1240 Mpc, membership of 73 quasars, and mean redshift <z> = 1.27. In terms of both size and membership it is the most extreme LQG found in the DR7QSO catalogue for the redshift range 1.0 <= z <= 1.8 of our current investigation. Its location on the sky is ~ 8.8 deg north (~ 615 Mpc projected) of the Clowes & Campusano LQG at the same redshift, <z> = 1.28, which is itself one of the more extreme examples. Their boundaries approach to within ~ 2 deg (~ 140 Mpc projected). This new, huge LQG appears to be the largest structure currently known in the early universe. Its size suggests incompatibility with the Yadav et al. scale of homogeneity for the concordance cosmology, and thus challenges the assumption of the cosmological principle.
Common extensions of the Standard Model of particle physics predict the existence of a "hidden" sector that comprises particles with a vanishing or very weak coupling to particles of the Standard Model (visible sector). For very light (m < 10^-14 eV) hidden U(1) gauge bosons (hidden photons), broad-band radio spectra of compact radio sources could be modified due to weak kinetic mixing with radio photons. Here, search methods are developed and their sensitivity discussed, with specific emphasis on the effect of the coherence length of the signal, instrumental bandwidth, and spectral resolution. We conclude that radio observations in the frequency range of 0.03--1400 GHz probe kinetic mixing of ~10^-3 of hidden photons with masses down to ~10^-17 eV. Prospects for improving the sensitivity with future radio astronomical facilities as well as by stacking data from multiple objects are discussed.
Analysis of laboratory experiments simulating space weathering optical effects on atmosphereless planetary bodies reveals that the time needed to alter the spectrum of an ordinary chondrite meteorite to resemble the overall spectral shape and slope of an S-type asteroid is about ~ 0.1 Myr. The time required to reduce the visible albedo of samples to ~ 0.05 is ~ 1 Myr. Since both these timescales are much less than the average collisional lifetime of asteroids larger than several kilometers in size, numerous low-albedo asteroids having reddish spectra with subdued absorption bands should be observed instead of an S-type dominated population. It is not the case because asteroid surfaces cannot be considered as undisturbed, unlike laboratory samples. We have estimated the number of collisions occurring in the time of 105 yr between asteroids and projectiles of various sizes and show that impact-activated motions of regolith particles counteract the progress of optical maturation of asteroid surfaces. Continual rejuvenation of asteroid surfaces by impacts does not allow bodies with the ordinary chondrite composition to be masked among S asteroids. Spectroscopic analysis, using relatively invariant spectral parameters, such as band centers and band area ratios, can determine whether the surface of an S asteroid has chondritic composition or not. Differences in the environment of the main asteroid belt versus that at 1 AU, and the physical difference between the Moon and main belt asteroids (i.e., size) can account for the lack of lunar-type weathering on main belt asteroids.
We report on an outburst of the high mass X-ray binary 4U 0115+63 with a pulse period of 3.6s in 2008 March/April as observed with RXTE and INTEGRAL. During the outburst the neutron star's luminosity varied by a factor of 10 in the 3--50\,keV band. In agreement with earlier work we find evidence for five cyclotron resonance scattering features at ~10.7, 21.8, 35.5, 46.7, and 59.7keV. Previous work had found an anti-correlation between the fundamental cyclotron line energy and the X-ray flux. We show that this apparent anti-correlation is probably due to the unphysical interplay of parameters of the cyclotron line with the continuum models used previously, e.g., the negative and positive exponent power law (NPEX). For this model, we show that cyclotron line modeling erroneously leads to describing part of the exponential cutoff and the continuum variability, and not the cyclotron lines. When the X-ray continuum is modeled with a simple exponentially cutoff power law modified by a Gaussian emission feature around 10keV, the correlation between the line energy and the flux vanishes and the line parameters remain virtually constant over the outburst. We therefore conclude that the previously reported anti-correlation is an artifact of the assumptions adopted in the modeling of the continuum.
Well over 700 exoplanets have been detected to date. Only a handful of these have been observed directly. Direct observation is extremely challenging due to the small separation and very large contrast involved. Imaging polarimetry offers a way to decrease the contrast between the unpolarized starlight and the light that has become linearly polarized after scattering by circumstellar material. This material can be the dust and debris found in circumstellar disks, but also the atmosphere or surface of an exoplanet. We present the design, calibration approach, polarimetric performance and sample observation results of the Extreme Polarimeter, an imaging polarimeter for the study of circumstellar environments in scattered light at visible wavelengths. The polarimeter uses the beam-exchange technique, in which the two orthogonal polarization states are imaged simultaneously and a polarization modulator swaps the polarization states of the two beams before the next image is taken. The instrument currently operates without the aid of Adaptive Optics. To reduce the effects of atmospheric seeing on the polarimetry, the images are taken at a frame rate of 35 fps, and large numbers of frames are combined to obtain the polarization images. Four successful observing runs have been performed using this instrument at the 4.2 m William Herschel Telescope on La Palma, targeting young stars with protoplanetary disks as well as evolved stars surrounded by dusty envelopes. In terms of fractional polarization, the instrument sensitivity is better than 10^-4. The contrast achieved between the central star and the circumstellar source is of the order 10^-6. We show that our calibration approach yields absolute polarization errors below 1%.
We determine approximate numerical integrals of motion of 2D symmetric Hamiltonian systems. We detail for a few gravitational potentials the conditions under which quasi-integrals are obtained as polynomial series. We show that each of these potentials has a wide range of regular orbits that are accurately modelled with a unique approximate integral of motion.
Observations of the X-ray pulsar 4U 2206+54, performed over a 15-year span, show its period, which is now 5555 \pm 9 s, to increase drastically. Such behavior of the pulsar can be hardly explained in the frame of traditional scenarios of spin evolution of compact stars. The observed spin-down rate of the neutron star in 4U 2206+54 proves to be in good agreement with the value expected within magnetic accretion scenario which takes into account that magnetic field of the accretion stream can under certain conditions affect its geometry and type of flow. The neutron star in this case accretes material from a dense gaseous slab with small angular momentum which is kept in equilibrium by the magnetic field of the flow itself. The magnetic accretion scenario can be realized in 4U 2206+54 provided the magnetic field strength on the surface of the optical counterpart to the neutron star is in excess of 70 G. The magnetic field strength on the surface of the neutron star in the frame of this scenario turns out to be 4 x 10^{12} G which is in accordance with estimates of this parameter from the analysis of X-ray spectra of the pulsar.
We examine the momentum dependence of the bispectrum of two-field inflationary models within the long-wavelength formalism. We determine the sources of scale dependence in the expression for the parameter of non-Gaussianity fNL and study two types of variation of the momentum triangle: changing its size and changing its shape. We introduce two spectral indices that quantify the possible types of momentum dependence of the local type fNL and illustrate our results with examples.
We study the presence of reversed polarity magnetic flux in sunspot penumbra. We applied a new regularized method to deconvolve spectropolarimetric data observed with the spectropolarimeter SP onboard Hinode. The new regularization is based on a principal component decomposition of the Stokes profiles. The resulting Stokes profiles were inverted to infer the magnetic field vector using SIR. We find, for the first time, reversed polarity fields at the border of many bright penumbral filaments in the whole penumbra.
We present the results of a search for high-energy gamma-ray emission from a large sample of galaxy clusters sharing the properties of three existing Fermi-LAT detections (in Perseus, Virgo and Abell 3392), namely a powerful radio source within their brightest cluster galaxy (BCG). From a parent, X-ray flux-limited sample of clusters, we select 114 systems with a core-dominated BCG radio flux above 50 or 75 mJy, stacking data from the first 45 months of the Fermi mission, to determine statistical limits on the gamma-ray fluxes of the ensemble of candidate sources. For a >300 MeV selection, the distribution of detection significance across the sample is consistent with that across control samples for significances <3 sigma, but has a tail extending to higher values, including three >4 sigma signals which are not associated with previously identified gamma-ray emission. Modelling of the data in these fields results in the detection of four non-2FGL Fermi sources, though none appear to be unambiguously associated with the BCG candidate. A search at energies >3 GeV hints at emission from the BCG in A 2055, which hosts a BL Lac object. There is no evidence for a signal in the stacked data, and the upper limit derived on the gamma-ray flux of an average radio-bright BCG in the sample is an order-of-magnitude more constraining than that calculated for individual objects. F(1 GeV)/F(1.4 GHz) <15, compared with ~120 for NGC 1275 in Perseus, which might indicate a special case for those objects detected at high energies; that beamed emission from member galaxies comprise the dominant bright gamma-ray sources in clusters.
The strength and direction of migration of low mass planets depends on the disc's thermodynamics. In discs where the viscous heating is balanced by radiative transport, the migration can be directed outwards, a process which extends the lifetime of growing planetary embryos. We investigate the influence of opacity and stellar irradiation on the disc thermodynamics. Utilizing the resulting disc structure, we determine the regions of outward migration. We perform two-dimensional numerical simulations of equilibrium discs with viscous heating, radiative cooling and stellar irradiation. We use the hydrodynamical code NIRVANA that includes a full tensor viscosity and stellar irradiation, as well as a two temperature solver that includes radiation transport in the flux-limited diffusion approximation. The migration is studied by using torque formulae. In the constant opacity case, we reproduce the analytical results of a black-body disc: the stellar irradiation dominates in the outer regions -- leading to flaring -- while the viscous heating dominates close to the star. We find that the inner edge of the disc should not be significantly puffed-up by the stellar irradiation. If the opacity depends on the local density and temperature, the structure of the disc is different, and several bumps in the aspect ratio H/r appear, due to transitions between different opacity regimes. The bumps in the disc can shield the outer disc from stellar irradiation. Stellar irradiation is an important factor for determining the disc structure and has dramatic consequences for the migration of embedded planets. Compared to discs with only viscous heating, a stellar irradiated disc features a much smaller region of outward migration for a range of planetary masses. This suggests that the region where the formation of giant planet cores takes place is smaller, which in turn might lead to a shorter growth phase.
This article presents a comparative analysis of solar activity data, Mt Wilson diameter data, Super-Kamiokande solar neutrino data, and nuclear decay data acquired at the Lomonosov Moscow State University (LMSU). We propose that salient periodicities in all of these datasets may be attributed to r-mode oscillations. Periodicities in the solar activity data and in Super-Kamiokande solar neutrino data may be attributed to r-mode oscillations in the known tachocline, with normalized radius in the range 0.66 to 0.74, where the sidereal rotation rate is in the range 13.7 to 14.6 year-1. We propose that periodicities in the Mt Wilson and LMSU data may be attributed to similar r-mode oscillations where the sidereal rotation rate is approximately which we attribute to a hypothetical inner tachocline separating a slowly rotating core from the radiative zone. We also discuss the possible role of the RSFP (Resonant Spin Flavor Precession) process, which leads to estimates of the neutrino magnetic moment and of the magnetic field strength in or near the solar core.
We present first results from the Herschel Gould Belt survey for the B211/L1495 region in the Taurus molecular cloud. Thanks to their high sensitivity and dynamic range, the Herschel images reveal the structure of the dense, star-forming filament B211 with unprecedented detail, along with the presence of striations perpendicular to the filament and generally oriented along the magnetic field direction as traced by optical polarization vectors. Based on the column density and dust temperature maps derived from the Herschel data, we find that the radial density profile of the B211 filament approaches a power-law behavior {\rho} {\propto} r^(-2.0{\pm}0.4) at large radii and that the temperature profile exhibits a marked drop at small radii. The observed density and temperature profiles of the B211 filament are in good agreement with a theoretical model of a cylindrical filament undergoing gravitational contraction with a polytropic equation of state: P {\propto} {\rho}^{\gamma} and T {\propto} {\rho}^({\gamma}-1), with {\gamma}=0.97{\pm}0.01<1 (i.e. not strictly isothermal). The morphology of the column density map, where some of the perpendicular striations are apparently connected to the B211 filament, further suggests that the material may be accreting along the striations onto the main filament. The typical velocities expected for the infalling material in this picture are ~0.5-1 km/s, which are consistent with the existing kinematical constraints from previous CO observations.
Context. Little is known about the properties of the warm (Tdust >~ 150 K) debris disk material located close to the central star, which has a more direct link to the formation of terrestrial planets than the low temperature debris dust that has been detected to date. Aims. To discover new warm debris disk candidates that show large 18 micron excess and estimate the fraction of stars with excess based on the AKARI/IRC Mid-Infrared All-Sky Survey data. Methods. We have searched for point sources detected in the AKARI/IRC All-Sky Survey, which show a positional match with A-M dwarf stars in the Tycho-2 Spectral Type Catalogue and exhibit excess emission at 18 micron compared to that expected from the Ks magnitude in the 2MASS catalogue. Results. We find 24 warm debris candidates including 8 new candidates among A-K stars. The apparent debris disk frequency is estimated to be 2.8 +/- 0.6%. We also find that A stars and solar-type FGK stars have different characteristics of the inner component of the identified debris disk candidates --- while debris disks around A stars are cooler and consistent with steady-state evolutionary model of debris disks, those around FGK stars tend to be warmer and cannot be explained by the steady-state model.
I show that for a substantial fraction of planets detected in a space-based survey, it would be possible to measure the planet and host masses and distances, if the survey satellite were placed in geosynchronous orbit. Such an orbit would enable measurement of the microlens parallax, \pi_e, for events with moderately low impact parameters, \beta <~ 0.05, which encompass a disproportionate share of planetary detections. Most planetary events yield a measurement of the angular Einstein radius \theta_e. Since the host mass is given by M=\theta_e/\kappa\pi_rel where \kappa\ is a constant, parallax measurements are the crucial missing link. I present simple analytic formulae that enable quick error estimates for observatories in circular orbits of arbitrary period and semi-major axis, and arbitrary orientation relative to the line of sight.
The stellar contents of the open clusters King 12, NGC 7788, and NGC 7790 are investigated using MegaCam images. Comparisons with isochrones yield an age < 20 Myr for King 12, 20--40 Myr for NGC 7788, and 60 -- 80 Myr for NGC 7790 based on the properties of stars near the main sequence turn-off (MSTO) in each cluster. The reddening of NGC 7788 is much larger than previously estimated. The luminosity functions (LFs) of King 12 and NGC 7788 show breaks that are attributed to the onset of pre-main sequence (PMS) objects, and comparisons with models of PMS evolution yield ages that are consistent with those measured from stars near the MSTO. In contrast, the r' LF of main sequence stars in NGC 7790 is matched to r' = 20 by a model that is based on the solar neighborhood mass function. The structural properties of all three clusters are investigated by examining the two-point angular correlation function of blue main sequence stars. King 12 and NGC 7788 are each surrounded by a stellar halo that extends out to 5 arcmin (~ 3.4 parsecs) radius. It is suggested that these halos form in response to large-scale mass ejection early in the evolution of the clusters, as predicted by models. In contrast, blue main sequence stars in NGC 7790 are traced out to a radius of ~ 7.5 arcmin, with no evidence of a halo. It is suggested that all three clusters may have originated in the same star-forming complex, but not in the same giant molecular cloud.
We present calculations of AGN winds at ~parsec scales, along with the associated obscuration. We take into account the pressure of infrared radiation on dust grains and the interaction of X-rays from a central black hole with hot and cold plasma. Infrared radiation (IR) is incorporated in radiation-hydrodynamic simulations adopting the flux-limited diffusion approximation. We find that in the range of X-ray luminosities L=0.05 - 0.6 L_edd, the Compton-thick part of the flow (aka torus) has an opening angle of approximately 72-75 degrees regardless of the luminosity. At L > 0.1 L_edd the outflowing dusty wind provides the obscuration with IR pressure playing a major role. The global flow consists of two phases: the cold flow at inclinations \theta > 70 degrees and a hot, ionized wind of lower density at lower inclinations. The dynamical pressure of the hot wind is important in shaping the denser IR supported flow. At luminosities <0.1 L_edd episodes of outflow are followed by extended periods when the wind switches to slow accretion.
Templates for polarised emission from Galactic foregrounds at frequencies relevant to Cosmic Microwave Background (CMB) polarisation experiments are obtained by modelling the Galactic Magnetic Field (GMF) on large scales. This work extends the results of O'Dea et al. by including polarised synchrotron radiation as a source of foreground emission. The polarisation direction and fraction in this calculation are based solely on the underlying choice of GMF model and therefore provide an independent prediction for the polarisation signal on large scales. Templates of polarised foregrounds may be of use when forecasting effective experimental sensitivity. In turn, as measurements of the CMB polarisation over large fractions of the sky become routine, this model will allow for the data to constrain parameters in the, as yet, not well understood form of the GMF.
Very high energy (VHE, energy >~ 100 GeV) {\gamma}-rays undergo pair production with photons of the extragalactic background light (EBL). Thus, the intrinsic {\gamma}-ray flux of cosmological sources is attenuated and the Universe should be opaque to {\gamma}-rays above a redshift dependent energy. Recently, an indication has been found that the Universe is more transparent than predicted by a lower-limit EBL model. Here, this indication is confronted with additional VHE {\gamma}-ray spectra and different EBL models. Depending on the model for the opacity, the indication persist between a ~2.6 {\sigma} and ~4.3 {\sigma} confidence level.
Very high energy (VHE, energy >~ 100 GeV) {\gamma}-rays originating from extragalactic sources interact with low energy photons of background radiation fields and produce electron-positron pairs. Alternatively, in the presence of ambient magnetic fields, they can convert into hypothetical axion-like particles (ALPs), pseudo-scalar spin-0 bosons, predicted by extensions of the standard model. These particles propagate unimpeded over cosmological distances. Here, the effect of photon-ALP oscillations in magnetic fields of galaxy clusters and the Milky Way on VHE {\gamma}-ray spectra is studied. It is shown that this mechanism can lead to a substantial enhancement of the VHE flux and a spectral hardening, thus effectively reducing the opacity of the Universe to VHE {\gamma}-rays.
Context. We investigate the statistics of the spatial and temporal distribution of the coronal heating in a three-dimensional magneto- hydrodynamical (3D MHD) model. The model describes the temporal evolution of the corona above an observed active region. The model is driven by photospheric granular motions which braid the magnetic field lines. This induces currents and their dissipation heats the plasma. We evaluate the transient heating as subsequent heating events and analyze their statistics. The results are then interpreted in the context of observed flare statistics and coronal heating mechanisms. Methods. To conduct the numerical experiment we use a high order finite difference code which solves the partial differential equations for the conservation of mass, the momentum and energy balance, and the induction equation. The energy balance includes the Spitzer heat conduction and the optical thin radiative loss in the corona. Results. The temporal and spatial distribution of the Ohmic heating in the 3D MHD model follow a power law and can therefore be explained by system in a self-organized critical state. The slopes of the power law are similar to the results based on flare observations. We find that the corona is heated foot point dominated and the coronal heating is dominated by events called nanoflares with energies on the order of 1017 J.
We present a comprehensive observational study of the gas phase metallicity of star-forming galaxies from z ~ 0 -> 3. We combine our new sample of gravitationally lensed galaxies with existing lensed and non-lensed samples to conduct a large investigation into the mass-metallicity (MZ) relation at z > 1. We apply a self-consistent metallicity calibration scheme to investigate the metallicity evolution of star-forming galaxies as a function of redshift. The lensing magnification ensures that our sample spans an unprecedented range of stellar mass (3*10^{7}-6*10^{10} M_sun). We find that at the median redshift of z=2.07, the median metallicity of the lensed sample is 0.35 dex lower than the local SDSS star-forming galaxies and 0.18 dex lower than the z ~ 0.8 DEEP2 galaxies. We also present the z ~ 2 MZ relation using 19 lensed galaxies. A more rapid evolution is seen between z ~ 1->3 than z ~ 0 -> 1 for the high-mass galaxies (10^{9.5-11} M_sun), with almost twice as much enrichment between z ~ 1 -> 3 than between z ~ 1 -> 0. We compare this evolution with the most recent cosmological hydrodynamic simulations with momentum driven winds. We find that the model metallicity is consistent with the observed metallicity within the observational error for the low mass bins. However, for higher masses, the model over-predicts the metallicity at all redshifts. The over-prediction is most significant in the highest mass bin of 10^{10-11} M_sun.
Coalescing binary black holes (BBHs) are among the most likely sources for the Laser Interferometer Gravitational-wave Observatory (LIGO) and its international partners Virgo and KAGRA. Optimal searches for BBHs require accurate waveforms for the signal model and effectual template banks that cover the mass space of interest. We investigate the ability of the second-order post-Newtonian TaylorF2 hexagonal template placement metric to construct an effectual template bank, if the template waveforms used are effective one body waveforms tuned to numerical relativity (EOBNRv2). We find that by combining the existing TaylorF2 placement metric with EOBNRv2 waveforms, we can construct an effectual search for BBHs with component masses in the range 3 Msolar <= m1, m2 <= 25 Msolar. We also show that the (computationally less expensive) TaylorF2 post-Newtonian waveforms can be used in place of EOBNRv2 waveforms when M <~ 12 Msolar. Finally, we investigate the effect of modes other than the dominant {l = m = 2} mode in BBH searches. We find that for systems with m1/m2 <= 1.5, there is no significant loss in the total possible signal-to-noise ratio due to neglecting modes greater than {l = m = 2} in the template waveforms. For higher mass ratios, including higher order modes could increase the signal-to-noise ratio by as much as 8% in Advanced LIGO. Our results can be used to construct matched-filter in Advanced LIGO and Advanced Virgo.
Models of chaotic inflation with a fractional power-law potential are not only viable but also testable in the foreseeable future. We show that such models can be realized in simple strongly coupled supersymmetric gauge theories. In these models, the energy scale during inflation is dynamically generated by the dimensional transmutation due to the strong gauge dynamics. Therefore, such models not only explain the origin of the fractional power in the inflationary potential but also provide a reason why the energy scale of inflation is much smaller than the Planck scale.
In the matter bounce scenario, a dust-dominated contracting space-time generates scale-invariant perturbations that, assuming a nonsingular bouncing cosmology, propagate to the expanding branch and set appropriate initial conditions for the radiation-dominated era. Since this scenario depends on the presence of a bounce, it seems appropriate to consider it in the context of loop quantum cosmology where a bouncing universe naturally arises. It turns out that quantum gravity effects play an important role beyond simply providing the bounce. Indeed, quantum gravity corrections to the Mukhanov-Sasaki equations significantly modify some of the results obtained in a purely classical setting: while the predicted spectra of scalar and tensor perturbations are both almost scale-invariant with identical small red tilts in agreement with previous results, the tensor to scalar ratio is now expected to be $10^{-4}$, which is much smaller than the original classical prediction. Finally, for the predicted amplitude of the scalar perturbations to agree with observations, the critical density in loop quantum cosmology must be of the order $10^{-9} \rho_{\rm Pl}$.
In this article we present some recent results on identifying correctly the relativistic multipole moments of numerically constructed spacetimes, and the consequences that this correction has on searching for appropriate analytic spacetimes that can approximate well the previously mentioned numerical spacetimes. We also present expressions that give the quadrupole and the spin octupole as functions of the spin parameter of a neutron star for various equations of state and in a range of masses for every equation of state used. These results are relevant for describing the exterior spacetime of rotating neutron stars that are made up of matter obeying realistic equations of state.
We extend the Induced Matter Theory of gravity (IMT) to 5D curved spacetimes by using the Weitzenb\"ock representation of connections on a 5D curved spacetime. In this representation the 5D curvature tensor becomes null, so that we can make static foliation on the extra noncompact coordinate to induce in the Weitzenb\"ock representation the Einstein equations. Once we done it, we can rewrite the effective 4D Einstein equations in the Levi-Civita representation. This generalization of IMT opens a huge window of possible applications for this theory. A pre-big bang collapsing scenario is explored as an example.
A few final comments on arXiv:1210.7548 are given to confute incorrect arguments claimed there.
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We describe implementation and tests of sink particle algorithms in the Eulerian grid-based code Athena. Introduction of sink particles enables long-term evolution of systems in which localized collapse occurs, and it is impractical (or unnecessary) to resolve the accretion shocks at the centers of collapsing regions. We discuss similarities and differences of our methods compared to other implementations of sink particles. Our criteria for sink creation are motivated by the properties of the Larson-Penston collapse solution. We use standard particle-mesh methods to compute particle and gas gravity together. Accretion of mass and momenta onto sinks is computed using fluxes returned by the Riemann solver. A series of tests based on previous analytic and numerical collapse solutions is used to validate our method and implementation. We demonstrate use of our code for applications with a simulation of planar converging supersonic turbulent flow, in which multiple cores form and collapse to create sinks; these sinks continue to interact and accrete from their surroundings over several Myr.
Self-Interacting Dark Matter is an attractive alternative to the Cold Dark Matter paradigm only if it is able to substantially reduce the central densities of dwarf-size haloes while keeping the densities and shapes of cluster-size haloes within current constraints. Given the seemingly stringent nature of the latter, it was thought for nearly a decade that SIDM would be viable only if the cross section for self-scattering was strongly velocity-dependent. However, it has recently been suggested that a constant cross section per unit mass of sigma_T/m~0.1cm^2/g is sufficient to accomplish the desired effect. We explicitly investigate this claim using high resolution cosmological simulations of a Milky-Way size halo and find that, similarly to the Cold Dark Matter case, such cross section produces a population of massive subhaloes that is inconsistent with the kinematics of the classical dwarf spheroidals, in particular with the inferred slopes of the mass profiles of Fornax and Sculptor. This problem is resolved if sigma_T/m~1cm^2/g at the dwarf spheroidal scales. Since this value is likely inconsistent with the halo shapes of several clusters, our results leave only a small window open for a velocity-independent Self-Interacting Dark Matter model to work as a distinct alternative to Cold Dark Matter.
It is commonly assumed that ground-based gravitational wave (GW) instruments will not be sensitive to supermassive black holes (SMBHs) because the characteristic GW frequencies are far below the ~ 10 - 1000 Hz sensitivity bands of terrestrial detectors. Here, however, we explore the possibility of SMBH gravitational waves to leak to higher frequencies. In particular, if the high frequency spectral tail asymptotes to h(f) ~ f^(-alpha), where alpha<=2, then the spectral amplitude is a constant or increasing function of the mass M at a fixed frequency f>>c^3/GM. This will happen if the time domain waveform or its derivative exhibits a discontinuity. Ground based instruments could search for these universal spectral tails to detect or rule out such features irrespective of their origin. We identify the following processes which may generate high frequency signals: (i) gravitational bremsstrahlung of ultrarelativistic objects in the vicinity of a SMBH, (ii) ringdown modes excited by an external process that has a high frequency component or terminates abruptly, (iii) gravitational lensing echos and diffraction. More specifically for (iii), SMBHs produce GW echos of inspiraling stellar mass binaries in galactic nuclei with a delay of a few minutes to hours. We estimate the order of magnitude of the detection signal to noise ratio for each mechanism (i, ii, and iii) as a function of the waveform parameters.
All massive galaxies likely have supermassive black holes at their centers, and the masses of the black holes are known to correlate with properties of the host galaxy bulge component. Several explanations have been proposed for the existence of these locally-established empirical relationships; they include the non-causal, statistical process of galaxy-galaxy merging, direct feedback between the black hole and its host galaxy, or galaxy-galaxy merging and the subsequent violent relaxation and dissipation. The empirical scaling relations are thus important for distinguishing between various theoretical models of galaxy evolution, and they further form the basis for all black hole mass measurements at large distances. In particular, observations have shown that the mass of the black hole is typically 0.1% of the stellar bulge mass of the galaxy. The small galaxy NGC4486B currently has the largest published fraction of its mass in a black hole at 11%. Here we report observations of the stellar kinematics of NGC 1277, which is a compact, disky galaxy with a mass of 1.2 x 10^11 Msun. From the data, we determine that the mass of the central black hole is 1.7 x 10^10 Msun, or 59% its bulge mass. Five other compact galaxies have properties similar to NGC 1277 and therefore may also contain over-sized black holes. It is not yet known if these galaxies represent a tail of a distribution, or if disk-dominated galaxies fail to follow the normal black hole mass scaling relations.
A massive, self-interacting scalar field has been considered as a possible candidate for the dark matter in the universe. We present an observational constraint to the model arising from strong lensing observations in galaxies. The result points to a discrepancy in the properties of scalar field dark matter halos for dwarf and lens galaxies, mainly because halo parameters are directly related to physical quantities in the model. This is an important indication that it becomes necessary to have a better understanding of halo evolution in scalar field dark matter models, where the presence of baryons can play an important role.
Numerical simulations have shown that the often cited radiation pressure barrier to accretion onto massive stars can be circumvented, when the radiation field is highly anisotropic in the presence of a circumstellar accretion disk with high optical depth. Here, these studies of the so-called flashlight effect are expanded by including the opacity of the innermost dust-free but potentially optically thick gas regions around forming massive stars. In addition to frequency-dependent opacities for the dust grains, we use temperature- and density-dependent Planck- and Rosseland mean opacities for the gas. The simulations show that the innermost dust-free parts of the accretion disks are optically thick to the stellar radiation over a substantial fraction of the solid angle above and below the disk's midplane. The temperature in the shielded disk region decreases faster with radius than in a comparison simulation with a lower constant gas opacity, and the dust sublimation front is shifted to smaller radii. The shielding by the dust-free gas in the inner disk thus contributes to an enhanced flashlight effect, which ultimately results in a smaller opening angle of the radiation pressure driven outflow and in a much longer timescale of sustained feeding of the circumstellar disk by the molecular cloud core. We conclude that it is necessary to properly account for the opacity of the inner dust-free disk regions around forming massive stars in order to correctly assess the effectiveness of the flashlight effect, the opening angle of radiation pressure driven outflows, and the lifetime and morphological evolution of the accretion disk.
We study the star formation efficiency (SFE) in simulations and observations of turbulent, magnetized, molecular clouds. We find that the volumetric and column density probability distributions (PDFs) of our simulations with solenoidal, mixed, and compressive forcing of turbulence, sonic Mach numbers of 3-50, and magnetic fields in the super- to the trans-Alfvenic regime, all develop power-law tails of flattening slope with increasing SFE. The high-density tails of the PDFs are consistent with equivalent radial density profiles, rho ~ r^(-kappa) with kappa ~ 1.5-2.5, in agreement with observations. Studying velocity-size scalings, we find that all the simulations are consistent with the observed v ~ l^(1/2) scaling of supersonic turbulence, and seem to approach Kolmogorov turbulence with v ~ l^(1/3) below the sonic scale. The velocity-size scaling is, however, largely independent of the SFE. In contrast, the density-size and column density-size scalings are highly sensitive to star formation. We find that the power-law slope alpha of the density power spectrum, P(rho,k) ~ k^alpha, or equivalently the Delta-variance spectrum of column density, DV(Sigma,l) ~ l^(-alpha), switches sign from alpha < 0 for SFE ~ 0 to alpha > 0 when star formation proceeds (SFE > 0). We provide a relation to compute the SFE from a measurement of alpha. Studying the literature, we find values ranging from alpha = -1.6 to +1.6 in observations covering scales from the large-scale atomic medium, over cold molecular clouds, down to dense star-forming cores. From those alpha values, we infer SFEs and find good agreement with independent measurements based on young stellar object (YSO) counts, where available. Our SFE-alpha relation provides an independent estimate of the SFE based on the column density map of a cloud alone, without requiring a priori knowledge of star-formation activity or YSO counts.
Future large-scale structure surveys of the Universe will aim to constrain the cosmological model and the true nature of dark energy with unprecedented accuracy. In order for these surveys to achieve their designed goals, they will require predictions for the nonlinear matter power spectrum to sub-percent accuracy. Through the use of a large ensemble of cosmological N-body simulations, we demonstrate that if we do not understand the uncertainties associated with simulating structure formation, i.e. knowledge of the `true' simulation parameters, and simply seek to marginalize over them, then the constraining power of such future surveys can be significantly reduced. However, for the parameters {n_s, h, Om_b, Om_m}, this effect can be largely mitigated by adding the information from a CMB experiment, like Planck. In contrast, for the amplitude of fluctuations sigma8 and the time-evolving equation of state of dark energy {w_0, w_a}, the mitigation is mild. On marginalizing over the simulation parameters, we find that the dark-energy figure of merit can be degraded by ~2. This is likely an optimistic assessment, since we do not take into account other important simulation parameters. A caveat is our assumption that the Hessian of the likelihood function does not vary significantly when moving from our adopted to the 'true' simulation parameter set. This paper therefore provides strong motivation for rigorous convergence testing of N-body codes to meet the future challenges of precision cosmology.
We characterize the incidence of active galactic nuclei (AGNs) is 0.3 < z < 1 star-forming galaxies by applying multi-wavelength AGN diagnostics (X-ray, optical, mid-infrared, radio) to a sample of galaxies selected at 70-micron from the Far-Infrared Deep Extragalactic Legacy survey (FIDEL). Given the depth of FIDEL, we detect "normal" galaxies on the specific star formation rate (sSFR) sequence as well as starbursting systems with elevated sSFR. We find an overall high occurrence of AGN of 37+/-3%, more than twice as high as in previous studies of galaxies with comparable infrared luminosities and redshifts but in good agreement with the AGN fraction of nearby (0.05 < z < 0.1) galaxies of similar infrared luminosities. The more complete census of AGNs comes from using the recently developed Mass-Excitation (MEx) diagnostic diagram. This optical diagnostic is also sensitive to X-ray weak AGNs and X-ray absorbed AGNs, and reveals that absorbed active nuclei reside almost exclusively in infrared-luminous hosts. The fraction of galaxies hosting an AGN appears to be independent of sSFR and remains elevated both on the sSFR sequence and above. In contrast, the fraction of AGNs that are X-ray absorbed increases substantially with increasing sSFR, possibly due to an increased gas fraction and/or gas density in the host galaxies.
Ongoing transient surveys are presenting an unprecedented account of the rising lightcurves of Type Ia supernovae (SNe Ia). This early emission probes the shallowest layers of the exploding white dwarf, which can provide constraints on the progenitor star and the properties of the explosive burning. We use semi-analytic models of radioactively-powered rising lightcurves to analyze these observations. As we have summarized in previous work, the main limiting factor in determining the surface distribution of 56Ni is the lack of an unambiguously identified time of explosion, as would be provided by detection of shock breakout or shock-heated cooling. Without this the SN may in principle exhibit a "dark phase" for a few hours to days, where the only emission is from shock-heated cooling that is too dim to be detected. Nevertheless, by considering the time-dependent velocity evolution, the explosion time can be better constrained, albeit with considerable uncertainty. This technique is used to infer the surface 56Ni distribution of three recent SNe Ia that were caught especially early in their rise. Although we cannot constrain the explosion times to better than ~1 day, in all three we find fairly similar 56Ni distributions. Observations of SN 2011fe and SN 2012cg probe shallower depths than in SN 2009ig, and in these two cases 56Ni is present merely ~0.01Msun from the WD's surface. We also use our conclusions about the explosion times to reassess radius constraints for the progenitor of SN 2011fe, as well as discuss the roughly t^2 power law that is inferred for many observed rising lightcurves.
We present the latest results from a spectroscopic survey designed to uncover
the hidden population of AM Canum Venaticorum (AM CVn) binaries in the
photometric database of the Sloan Digital Sky Survey (SDSS). We selected ~2000
candidates based on their photometric colours, a relatively small sample which
is expected to contain the majority of all AM CVn binaries in the SDSS
(expected to be ~50).
We present two new candidate AM CVn binaries discovered using this strategy:
SDSS J104325.08+563258.1 and SDSS J173047.59+554518.5. We also present spectra
of 29 new cataclysmic variables, 23 DQ white dwarfs and 21 DZ white dwarfs
discovered in this survey.
The survey is now approximately 70 per cent complete, and the discovery of
seven new AM CVn binaries indicates a lower space density than previously
predicted. From the essentially complete g <= 19 sample, we derive an observed
space density of (5 +/- 3) x10^-7 pc^-3; this is lower than previous estimates
by a factor of 3.
The sample has been cross-matched with the GALEX All-Sky Imaging Survey
database, and with Data Release 9 of the UKIRT (United Kingdom Infrared
Telescope) Infrared Deep Sky Survey (UKIDSS). The addition of UV photometry
allows new colour cuts to be applied, reducing the size of our sample to ~1100
objects. Optimising our followup should allow us to uncover the remaining AM
CVn binaries present in the SDSS, providing the larger homogeneous sample
required to more reliably estimate their space density.
We have constructed a sample of radio-loud objects with optical spectroscopy from the Galaxy and Mass Assembly (GAMA) project over the Herschel-ATLAS Phase 1 fields. Classifying the radio sources in terms of their optical spectra, we find that strong-emission-line sources (`high-excitation radio galaxies') have, on average, a factor ~4 higher 250-micron Herschel luminosity than weak-line (`low-excitation') radio galaxies and are also more luminous than magnitude-matched radio-quiet galaxies at the same redshift. Using all five H-ATLAS bands, we show that this difference in luminosity between the emission-line classes arises mostly from a difference in the average dust temperature; strong-emission-line sources tend to have comparable dust masses to, but higher dust temperatures than, radio galaxies with weak emission lines. We interpret this as showing that radio galaxies with strong nuclear emission lines are much more likely to be associated with star formation in their host galaxy, although there is certainly not a one-to-one relationship between star formation and strong-line AGN activity. The strong-line sources are estimated to have star-formation rates at least a factor 3-4 higher than those in the weak-line objects. Our conclusion is consistent with earlier work, generally carried out using much smaller samples, and reinforces the general picture of high-excitation radio galaxies as being located in lower-mass, less evolved host galaxies than their low-excitation counterparts.
We present N-body simulations of intermediate-mass (3000-4000 Msun) young star clusters (SCs) with three different metallicities (Z=0.01, 0.1 and 1 Zsun), including metal-dependent stellar evolution recipes and binary evolution. Following recent theoretical models of wind mass loss and core collapse supernovae, we assume that the mass of the stellar remnants depends on the metallicity of the progenitor stars. In particular, massive metal-poor stars (Z<=0.3 Zsun) are enabled to form massive stellar black holes (MSBHs, with mass >=25 Msun) through direct collapse. We find that three-body encounters, and especially dynamical exchanges, dominate the evolution of the MSBHs formed in our simulations. In SCs with Z=0.01 and 0.1 Zsun, about 75 per cent of simulated MSBHs form from single stars and become members of binaries through dynamical exchanges in the first 100 Myr of the SC life. This is a factor of >~3 more efficient than in the case of low-mass (<25 Msun) stellar black holes. A small but non-negligible fraction of MSBHs power wind-accreting (10-20 per cent) and Roche lobe overflow (RLO, 5-10 per cent) binary systems. The vast majority of MSBH binaries that undergo wind accretion and/or RLO were born from dynamical exchange. This result indicates that MSBHs can power X-ray binaries in low-metallicity young SCs, and is very promising to explain the association of many ultraluminous X-ray sources with low-metallicity and actively star forming environments.
We report the results of an X-ray proper motion measurement for the NW rim of SN1006, carried out by comparing Chandra observations from 2001 and 2012. The NW limb has predominantly thermal X-ray emission, and it is the only location in SN1006 with significant optical emission: a thin, Balmer-dominated filament. For most of the NW rim, the proper motion is about 0.30 arcsec/yr, essentially the same as has been measured from the H-alpha filament. Isolated regions of the NW limb are dominated by nonthermal emission, and here the proper motion is much higher, 0.49 arcsec/yr, close to the value measured in X-rays along the much brighter NE limb, where the X-rays are overwhelmingly nonthermal. At the 2.2 kpc distance to SN1006, the proper motions imply shock velocities of about 3000 km/s and 5000 km/s in the thermal and nonthermal regions, respectively. A lower velocity behind the H-alpha filament is consistent with the picture that SN1006 is encountering denser gas in the NW, as is also suggested by its overall morphology. In the thermally-dominated portion of the X-ray shell, we also see an offset in the radial profiles at different energies; the 0.5-0.6 keV peak dominated by O VII is closer to the shock front than that of the 0.8-3 keV emission--due to the longer times for heavier elements to reach ionization states where they produce strong X-ray emission.
Since 1998, a planet-search program around main sequence stars within 50 pc in the southern hemisphere, is carried out with the CORALIE echelle spectrograph at La Silla Observatory. With an observing time span of more than 14 years, the CORALIE survey is now able to unveil Jovian planets on Jupiter's period domain. This growing period-interval coverage is important regarding to formation and migration models since observational constraints are still weak for periods beyond the ice line. Long-term precise Doppler measurements with the CORALIE echelle spectrograph, together with a few additional observations made with the HARPS spectrograph on the ESO 3.6m telescope, reveal radial velocity signatures of massive planetary companions in long period orbits. In this paper we present seven new planets orbiting HD27631, HD98649, HD106515A, HD166724, HD196067, HD219077, and HD220689 together with the CORALIE orbital parameters for three already known planets around HD10647, HD30562, and HD86226. The period range of the new planetary companions goes from 2200 to 5500 days and covers a mass domain between 1 and 10.5 MJup. Surprisingly, five of them present quite high eccentricities above e>0.57. A pumping scenario by Kozai mechanism may be invoked for HD106515Ab and HD196067b which are both orbiting stars in multiple systems. As the presence of a third massive body can't be inferred from the data of HD98649b, HD166724b, and HD219077b, the origin of the eccentricity of these systems remains unknown. Except for HD10647b, no constraint on the upper mass of the planets is provided by Hipparcos astrometric data. Finally it is interesting to note that the hosts of these long period planets show no metallicity excess.
The CXOCY J220132.8-320144 system consists of an edge-on spiral galaxy lensing a background quasar into two bright images. Previous efforts to constrain the mass distribution in the galaxy have suggested that at least one additional image must be present (Castander et al. 2006). These extra images may be hidden behind the disk which features a prominent dust lane. We present and analyze Hubble Space Telescope (HST) observations of the system. We do not detect any extra images, but the observations further narrow the observable parameters of the lens system. We explore a range of models to describe the mass distribution in the system and find that a variety of acceptable model fits exist. All plausible models require 2 magnitudes of dust extinction in order to obscure extra images from detection, and some models may require an offset between the center of the galaxy and the center of the dark matter halo of 1 kiloparsec. Currently unobserved images will be detectable by future James Webb Space Telescope (JWST) observations and will provide strict constraints on the fraction of mass in the disk.
Aiming to correctly restore the redshifted 21 cm signals emitted by the neutral hydrogen during the cosmic reionization processes, we re-examine the separation approaches based on the quadratic polynomial fitting technique in frequency space to investigate whether they works satisfactorily with complex foreground, by quantitatively evaluate the quality of restored 21 cm signals in terms of sample statistics. We construct the foreground model to characterize both spatial and spectral substructures of the real sky, and use it to simulate the observed radio spectra. By comparing between different separation approaches through statistical analysis of restored 21 cm spectra and corresponding power spectra, as well as their constraints on the mean halo bias $b$ and average ionization fraction $x_e$ of the reionization processes, at $z=8$ and the noise level of 60 mK we find that, although the complex foreground can be well approximated with quadratic polynomial expansion, a significant part of Mpc-scale components of the 21 cm signals (75% for $\gtrsim 6h^{-1}$ Mpc scales and 34% for $\gtrsim 1h^{-1}$ Mpc scales) is lost because it tends to be mis-identified as part of the foreground when single-narrow-segment separation approach is applied. The best restoration of the 21 cm signals and the tightest determination of $b$ and $x_e$ can be obtained with the three-narrow-segment fitting technique as proposed in this paper. Similar results can be obtained at other redshifts.
I review the early development of Aperture Arrays and their role in radio astronomy. The demise of this technology at the end of the 1960's, and the reasons for the rise of parabolic dishes is also considered. The parallels with the Antikythera mechanism (see these proceedings) as a lost technology are briefly presented. Aperture Arrays re-entered the world of radio astronomy as the idea to build a huge radio telescope with a collecting area of one square kilometre (the Square Kilometre Array, SKA) arose. Huge ICT technology advances had transformed Aperture Arrays in terms of their capability, flexibility and reliability. In the mid-1990s, ASTRON started to develop and experiment with the first high frequency aperture array tiles for radio astronomy - AAD, OSMA, THEA & EMBRACE. In the slipstream of these efforts, Phased Array Feeds (PAFs) for radio astronomy were invented and LOFAR itself emerged as a next generation telescope and a major pathfinder for the SKA. Meanwhile, the same advantages that aperture arrays offered to radio astronomy had already made dishes obsolete in many different civilian and military applications. The first commissioning results from LOFAR and other Aperture Arrays (MWA, LWA and PAPER) currently demonstrate that this kind of technology can transform radio astronomy over 2 decades of the radio spectrum, and at frequencies up to at least 1.5 GHz. This "reinvention of radio astronomy" has important implications for the design and form of the full SKA. Building a SKA that is simply the "VLA on steroids" is simply not good enough. Like the Antikythera mechanism itself, we must amaze future generations of astronomers - they and the current generation deserve nothing less.
We report our search for \gamma-ray emission in the energy range from 100 MeV to 300 GeV from four Accreting Millisecond Pulsars (AMPs), SAX J1808.4-3658, IGR J00291+5934, XTE J1814-338, and XTE J0929-314. The data are from four-year observations carried out by Large Area Telescope (LAT) onboard the Fermi \gamma-ray Space Telescope. The AMPs were not detected, and their \gamma-ray luminosity upper limits we obtain are 5.1*10^33 ergs/s for SAX J1808.4-3658, 2.1*10^33 ergs/s for IGR J00291+5934, 1.2*10^34 ergs/s for XTE J1814-338, and 2.2*10^33 ergs/s for XTE J0929-314. We compare our results with \gamma-ray irradiation luminosities required for producing optical modulations seen from the companions in the AMPs, which has been suggested by Takata et al. (2012), and our upper limits have excluded \gamma-ray emission as the heating source in these systems except XTE J0929-314, the upper limit of which is not deep enough. Our results also do not support the model proposed by Takata et al. (2012) that relatively strong \gamma-ray emission could arise from the outer gap of a high-mass neutron star controlled by the photon-photon pair-creation for the AMPs. Two AMPs, SAX J1808.4-3658 and IGR J00291+5934, have the measurements of their spin-down rates, and we derive the upper limits of their \gamma-ray conversion efficiencies, which are 57% and 3%, respectively. We discuss the implications to the AMP systems by comparing the efficiency upper limit values with that of 20 \gamma-ray millisecond pulsars (MSP) detected by Fermi and the newly discovered transitional MSP binary J1023+0038.
White and brown dwarfs are astrophysical objects that are bright enough to support an insolation habitable zone (IHZ). Unlike hydrogen-burning stars, they cool and become less luminous with time, and hence their IHZ moves in with time. The inner edge of the IHZ is defined as the orbital radius at which a planet may enter a moist or runaway greenhouse, phenomena that can remove a planet's surface water forever. Thus, as the IHZ moves in, planets that enter it may no longer have any water, and are still uninhabitable. Additionally, the close proximity of the IHZ to the primary leads to concern that tidal heating may also be strong enough to trigger a runaway greenhouse, even for orbital eccentricities as small as 10^-6. Water loss occurs due to photolyzation by UV photons in the planetary stratosphere, followed by hydrogen escape. Young white dwarfs emit a large amount of these photons as their surface temperatures are over 10^4 K. The situation is less clear for brown dwarfs, as observational data do not constrain their early activity and UV emission very well. Nonetheless, both types of planets are at risk of never achieving habitable conditions, but planets orbiting white dwarfs may be less likely to sustain life than those orbiting brown dwarfs. We consider the future habitability of the planet candidates KOI 55.01 and 55.02 in these terms and find they are unlikely to become habitable.
In the cm-wavelength range, an extraterrestrial electromagnetic narrow band (sine wave) beacon is an excellent choice to get alien attention across interstellar distances because 1) it is not strongly affected by interstellar / interplanetary dispersion or scattering, and 2) searching for narrowband signals is computationally efficient (scales as Ns log(Ns) where Ns = number of voltage samples). Here we consider a special case wideband signal where two or more delayed copies of the same signal are transmitted over the same frequency and bandwidth, with the result that ISM dispersion and scattering cancel out during the detection stage. Such a signal is both a good beacon (easy to find) and carries arbitrarily large information rate (limited only by the atmospheric transparency to about 10 GHz). The discovery process uses an autocorrelation algorithm, and we outline a compute scheme where the beacon discovery search can be accomplished with only 2x the processing of a conventional sine wave search, and discuss signal to background response for sighting the beacon. Once the beacon is discovered, the focus turns to information extraction. Information extraction requires similar processing as for generic wideband signal searches, but since we have already identified the beacon, the efficiency of information extraction is negligible.
We have studied the opacity of dust grains at submillimeter wavelengths by estimating the optical depth from imaging at 160, 250, 350, and 500 um from the Herschel Gould Belt Survey and comparing this to a column density obtained from the 2MASS-derived color excess E(J-Ks). Our main goal was to investigate the spatial variations of the opacity due to "big" grains over a variety of environmental conditions and thereby quantify how emission properties of the dust change with column (and volume) density. The central and southern areas of the Orion A molecular cloud examined here, with NH ranging from 1.5X10^21 cm^-2 to 50X10^21 cm^-2, are well suited to this approach. We fit the multi-frequency Herschel spectral energy distributions (SEDs) of each pixel with a modified blackbody to obtain the temperature, T, and optical depth, \tau(1200), at a fiducial frequency of 1200 GHz (250 um). Using a calibration of NH/E(J-Ks)for the interstellar medium (ISM) we obtained the opacity (dust emission cross-section per H nucleon), \sigma_e(1200), for every pixel. From a value of ~ 1X10^-25 cm^2 H^-1 at the lowest column densities that is typical of the high latitude diffuse ISM, \sigma_e(1200) increases as NH^0.28 over the range studied. This is suggestive of grain evolution. Integrating the SEDs over frequency, we also calculated the specific power P (emission power per H) for the big grains. In low column density regions where dust clouds are optically thin to the interstellar radiation field (ISRF), P is typically 3.7 X 10^-31 W H^-1, again close to that in the high latitude diffuse ISM. However, we find evidence for a decrease of P in high column density regions, which would be a natural outcome of attenuation of the ISRF that heats the grains, and for localized increases for dust illuminated by nearby stars or embedded protostars.
In a previous paper, we connected the phenomenological non-commutative inflation of Alexander, Brandenberger and Magueijo (2003, 2005 and 2007) with the formal representation theory of groups and algebras. In that paper, the fundamental equations of inflation followed as a consequence of a deformation of the Poincar\'e group, which induces a particular quantum representation. In this paper, we show that there exists a conceptual problem with the kind of representation that leads to the fundamental equations of the model and that the procedure to obtain those equations should be modified according to one of two possible proposals. One of them relates to the general theory of Hopf algebras. The other is based on a representation theorem of Von Neumann algebras, a proposal already suggested by us to take into account interactions in the inflationary equation of state. This reopens the problem of finding inflationary deformed dispersion relations and all developments which followed the first paper of Non-commutative Inflation.
Four transits of the exoplanet HAT-P-23b were recently observed with the 0.36m telescope at the Universidad de Monterrey Observatory. The four light curves were successfully combined to obtain a resulting one with reduced scattering per bin. This one was modeled using a Monte Carlo method to obtain the essential parameters that characterize the system. Assuming orbital parameters such as eccentricity, e, and longitude of periastron, w, from the discovery paper, we found values of Rp/R* = 0.1105 +0.0015-0.0013 for the planet-to-star radius ratio, a/R* = 4.23 +0.06-0.12 for the scaled semimajor axis, and an orbital inclination of the system of i = 87.9d +1.5-2.2. We also derive an improved orbital period of 1.2128868 +- 0.0000004 days (To = 2,454,852.26542 +- 0.00018 BJD_TDB) for the system.
Using density functional molecular dynamics free energy calculations, we show that the body-centered-cubic phase of superionic ice previously believed to be the only phase is in fact thermodynamically unstable compared to a novel phase with oxygen positions in fcc lattice sites. The novel phase has a lower proton mobility than the bc phase and may exhibit a higher melting temperature. We predict a transition between the two phases at a pressure of 1 +/- 0.5 Mbar, with potential consequences for the interiors of ice giants such as Uranus and Neptune.
Together with the development of the Large APEX Bolometer Camera (LABOCA) for the Atacama Pathfinder Experiment (APEX), a new data reduction package has been written. This software naturally interfaces with the telescope control system, and provides all functionalities for the reduction, analysis and visualization of bolometer data. It is used at APEX for real time processing of observations performed with LABOCA and other bolometer arrays, providing feedback to the observer. Written in an easy-to-script language, BoA is also used offline to reduce APEX continuum data. In this paper, the general structure of this software is presented, and its online and offline capabilities are described.
Recent quasar microlensing observations have constrained the sizes of X-ray emission regions to be within about 10 gravitational radii of the central supermassive black hole. Therefore, the X-ray emission from lensed quasars is first strongly lensed by the black hole before it is lensed by the foreground galaxy and star fields. We present a scheme that combines the initial strong lensing of a Kerr black hole with standard linearized microlensing by intervening stars. We find that X-ray microlensed light curves incorporating Kerr strong gravity can differ significantly from standard curves. The amplitude of the fluctuations in the light curves can increase or decrease by ~0.65-0.75 mag by including Kerr strong gravity. Larger inclination angles give larger amplitude fluctuations in the microlensing light curves. Consequently, current X-ray microlensing observations might have under or overestimated the sizes of the X-ray emission regions. We estimate this bias using a simple metric based on the amplitude of magnitude fluctuations. The half light radius of the X-ray emission region can be underestimated up to ~50% or overestimated up to ~20%. Underestimates are found in most situations we have investigated. The only exception is for a disk with large spin, radially flat emission profile, and observed nearly face on, where an overestimate is found. Thus, more accurate microlensing size constraints should be obtainable by including Kerr lensing. The caustic crossing time can differ by months after including Kerr strong gravity. A simultaneous monitoring of gravitational lensed quasars in both X-ray and optical bands with densely sampled X-ray light curves might reveal this feature. We conclude that it should be possible to constrain important parameters such as inclination angles and black hole spins from combined Kerr and microlensing effects.
(Abridged) The Census of High- and Medium-mass Protostars (CHaMP) is the first large-scale (280 degree<l<300 degree, -4 degree<b<2 degree), unbiased, survey of massive molecular clumps in the Milky Way at ~pc scale using 90 and 110 GHz line emission. Barnes et al. (2011, Paper I) presented the catalog of ~300 dense molecular clumps from Mopra HCO+(1-0) maps. Here we use archival Spitzer, MSX, IRAS and mm continuum data to derive bolometric luminosities, L of these clumps. We evaluate the ratio, L/M, where M is the mass derived from HCO+(1-0) emission. We find the clumps have 10Lsun<L<1E6.5Lsun and 0.1<L/M<1E3. These values are consistent with theoretical expectations of a clump population that spans a range of instantaneous star formation efficiencies from 0 to ~50%. We thus expect L/M to be a good (i.e. strongly varying) evolutionary indicator of the star cluster formation process. We find significant correlations of the ratio of warm to cold component flux and of the cold component temperature with L/M. We also find a near linear relation between Spitzer-IRAC specific intensity and L/M, and so we propose its use as an empirical star formation efficiency indicator. The lower bound of the distribution of L/M suggests the star formation efficiency per free-fall time is <0.2. Similar to previous studies, we find a linear relation between L and dense gas mass as measured by HCO+(1-0) line luminosity, L_HCO+(1-0). The sensitive nature of the CHaMP survey allows us to explore this relation down to much lower luminosity, ~30 Lsun, than before. Fitting together with extragalactic systems, the linear relation still holds, extending over 10 orders of magnitude in luminosity. The complete nature of the CHaMP survey over a several kiloparsec extent also allows us to derive an intermediate measurement that bridges the scales of individual clumps and whole galaxies.
Galaxy clusters are the most massive objects in the universe, and they comprise a high temperature intracluster medium of about $10^7$K, believed to offer a main foreground effect for the CMB data with thermal Sunyaev-Zel'dovich (SZ) effect. This assumption has been confirmed with SZ signal detection in hundreds of clusters, but comparing with the huge numbers of clusters within optical selected samples from SDSS data, this only accounts for a few percent. Here we introduce a model-independent new method to confirm the assumption that galaxy clusters offer the thermal SZ signal as their main foreground effect. For the WMAP 7year data, we classified data pixels as "to be" or "not to be" affected by the sample clusters, with a parameter of its nearest neighbor cluster's angular distance. By comparing the statistical results of these two kinds of pixels, we can see how the sample clusters affect the CMB data directly. We find that Planck-ESZ sample and the Xray samples($\sim10^2$ clusters) can lead to obvious temperature depression in WMAP 7year data, this confirms the SZ effect prediction. However, each optical selected sample ($> 10^4$ clusters), shows an opposite result: the mean temperature rises to about 10 uK. The unexpected qualitative scenario implies that the main foreground effect of most clusters is NOT always the expected SZ effect. This is maybe the reason why the SZ signal detection result is lower than what is expected by the model.
Recent Solar Dynamic Observatory observations reveal that coronal mass ejections (CMEs) consist of a multi-temperature structure: a hot flux rope and a cool leading front (LF). The flux rope first appears as a twisted hot channel in the Atmospheric Imaging Assembly 94 A and 131 A passbands. The twisted hot channel initially lies along the polarity inversion line and then rises and develops into the semi-circular flux rope-like structure during the impulsive acceleration phase of CMEs. In the meantime, the rising hot channel compresses the surrounding magnetic field and plasma, which successively stack into the CME LF. In this paper, we study in detail two well-observed CMEs occurred on 2011 March 7 and 2011 March 8, respectively. Each of them is associated with an M-class flare. Through a kinematic analysis we find that: (1) the hot channel rises earlier than the first appearance of the CME LF and the onset of the associated flare; (2) the speed of the hot channel is always faster than that of the LF, at least in the field of view of AIA. Thus, the hot channel acts as a continuous driver of the CME formation and eruption in the early acceleration phase. Subsequently, the two CMEs in white-light images can be well reproduced by the graduated cylindrical shell flux rope model. These results suggest that the pre-existing flux rope plays a key role in CME initiation and formation.
To understand the effects of the initial rotation on the evolution of the tidally limited clusters with mass spectrum, we have performed N-body simulations of the clusters with different initial rotations and compared the results with those of the Fokker-Planck (FP) simulations. We confirmed that the cluster evolution is accelerated by not only the initial rotation but also the mass spectrum. For the slowly rotating models, the time evolutions of mass, energy and angular momentum show good agreements between N-body and FP simulations. On the other hand, for the rapidly rotating models, there are significant differences between these two approaches at the early stage of the evolutions because of the development of bar instability in N-body simulations. The shape of the cluster for N-body simulations becomes tri-axial or even prolate, which cannot be produced by the 2-dimensional FP simulations. The total angular momentum and the total mass of the cluster decrease rapidly while bar-like structure persists. After the rotational energy becomes smaller than the critical value for the bar instability, the shape of the cluster becomes nearly axisymmetric again, and follows the evolutionary track predicted by the FP equation. We have confirmed again that the energy equipartiton is not completely achieved when M2/M1(m2>/m1)^(3/2) > 0.16. By examining the angular momentum at each mass component, we found that the exchange of angular momentum between different mass components occurs, similar to the energy exchange leading to the equipartition.
In 2006, Prochter et al. reported a statistically significant enhancement of very strong Mg II absorption systems intervening the sightlines to gamma-ray bursts (GRBs) relative to the in- cidence of such absorption along quasar sightlines. This counterintuitive result, has inspired a diverse set of astrophysical explanations (e.g. dust, gravitational lensing) but none of these has obviously resolved the puzzle. Using the largest set of GRB afterglow spectra available, we reexamine the purported enhancement. In an independent sample of GRB spectra with a survey path 3 times larger than Prochter et al., we measure the incidence per unit redshift of $\geq 1$\AA rest-frame equivalent width Mg II absorbers at $z \approx 1$ to be l(z)= 0.18 $\pm$ 0.06. This is fully consistent with current estimates for the incidence of such absorbers along quasar sightlines. Therefore, we do not confirm the original enhancement and suggest those results suffered from a statistical fluke. Signatures of the original result do remain in our full sample (l(z) shows an $\approx 1.5$ enhancement over l(z)QSO), but the statistical significance now lies at $\approx 90%$ c.l. Restricting our analysis to the subset of high-resolution spectra of GRB afterglows (which overlaps substantially with Prochter et al.), we still reproduce a statistically significant enhancement of Mg II absorption. The reason for this excess, if real, is still unclear since there is no connection between the rapid afterglow follow-up process with echelle (or echellette) spectrographs and the detectability of strong Mg II doublets. Only a larger sample of such high-resolution data will shed some light on this matter.
We study the case of a bright (L>L*) barred spiral galaxy from the rich cluster A3558 in the Shapley supercluster core (z=0.05) undergoing ram-pressure stripping. Integral-field spectroscopy, complemented by multi-band imaging, allows us to reveal the impact of ram pressure on the interstellar medium. We study in detail the kinematics and the physical conditions of the ionized gas and the properties of the stellar populations. We observe one-sided extraplanar ionized gas along the full extent of the galaxy disc. Narrow-band Halpha imaging resolves this outflow into a complex of knots and filaments. The gas velocity field is complex with the extraplanar gas showing signature of rotation. In all parts of the galaxy, we find a significant contribution from shock excitation, as well as emission powered by star formation. Shock-ionized gas is associated with the turbulent gas outflow and highly attenuated by dust. All these findings cover the whole phenomenology of early-stage ram-pressure stripping. Intense, highly obscured star formation is taking place in the nucleus, probably related to the bar, and in a region 12 kpc South-West from the centre. In the SW region we identify a starburst characterized by a 5x increase in the star-formation rate over the last ~100 Myr, possibly related to the compression of the interstellar gas by the ram pressure. The scenario suggested by the observations is supported and refined by ad hoc N-body/hydrodynamical simulations which identify a rather narrow temporal range for the onset of ram-pressure stripping around t~60 Myr ago, and an angle between the galaxy rotation axis and the intra-cluster medium wind of ~45 deg. Taking into account that the galaxy is found ~1 Mpc from the cluster centre in a relatively low-density region, this study shows that ram-pressure stripping still acts efficiently on massive galaxies well outside the cluster cores.
In this review, our present day understanding of the Sun's global photospheric and coronal magnetic fields is discussed from both observational and theoretical viewpoints. Firstly, the large-scale properties of photospheric magnetic fields are described, along with recent advances in photospheric magnetic flux transport models. Following this, the wide variety of theoretical models used to simulate global coronal magnetic fields are described. From this, the combined application of both magnetic flux transport simulations and coronal modeling techniques to describe the phenomena of coronal holes, the Sun's open magnetic flux and the hemispheric pattern of solar filaments is discussed. Finally, recent advances in non-eruptive global MHD models are described. While the review focuses mainly on solar magnetic fields, recent advances in measuring and modeling stellar magnetic fields are described where appropriate. In the final section key areas of future research are identified.
Context. Transit detection algorithms are mathematical tools used for detecting planets in the photometric data of transit surveys. In this work we study their application to space-based surveys. Aims: Space missions are exploring the parameter space of the transit surveys where classical algorithms do not perform optimally, either because of the challenging signal-to-noise ratio of the signal or its non-periodic characteristics. We have developed an algorithm addressing these challenges for the mission CoRoT. Here we extend the application to the data from the space mission Kepler. We aim at understanding the performances of algorithms in different data sets. Methods: We built a simple analytical model of the transit signal and developed a strategy for the search that improves the detection performance for transiting planets. We analyzed Kepler data with a set of stellar activity filtering and transit detection tools from the CoRoT community that are designed for the search of transiting planets. Results: We present a new algorithm and its performances compared to one of the most widely used techniques in the literature using CoRoT data. Additionally, we analyzed Kepler data corresponding to quarter Q1 and compare our results with the most recent list of planetary candidates from the Kepler survey. We found candidates that went unnoticed by the Kepler team when analyzing longer data sets. We study the impact of instrumental features on the production of false alarms and false positives. These results show that the analysis of space mission data advocates the use of complementary detrending and transit detection tools also for future space-based transit surveys such as PLATO.
Context. The properties of dust grains, in particular their size distribution, are expected to differ from the interstellar medium to the high-density regions within molecular clouds. Aims. We measure the mid-infrared extinction law produced by dense material in molecular cloud cores. Since the extinction at these wavelengths is caused by dust, the extinction law in cores should depart from that found in low-density environments if the dust grains have different properties. Methods. We use the unbiased LINES method to measure the slope of the reddening vectors in color-color diagrams. We derive the mid-infrared extinction law toward the dense cores B59 and FeSt 1-457 in the Pipe Nebula over a range of visual extinction between 10 and 50 magnitudes, using a combination of Spitzer/IRAC, and ESO NTT/VLT data. Results. The mid-infrared extinction law in both cores departs significantly from a power-law between 3.6 and 8 micron, suggesting that these cores contain dust with a considerable fraction of large dust grains. We find no evidence for a dependence of the extinction law with column density up to 50 magnitudes of visual extinction in these cores, and no evidence for a variation between our result and those for other clouds at lower column densities reported elsewhere in the literature. This suggests that either large grains are present even in low column density regions, or that the existing dust models need to be revised at mid-infrared wavelengths. We find a small but significant difference in the extinction law of the two cores, that we tentatively associate with the onset of star formation in B59.
Solar tornados are dynamical, conspicuously helical magnetic structures mainly observed as a prominence activity. We investigate and propose a triggering mechanism for the solar tornado observed in a prominence cavity by SDO/AIA on September 25, 2011. High-cadence EUV images from the SDO/AIA and the Ahead spacecraft of STEREO/EUVI are used to correlate three flares in the neighbouring active-region (NOAA 11303), and their EUV waves, with the dynamical developments of the tornado. The timings of the flares and EUV waves observed on-disk in 195\AA\ are analyzed in relation to the tornado activities observed at the limb in 171\AA. Each of the three flares and its related EUV wave occurred within 10 hours of the onset of the tornado. They have an observed causal relationship with the commencement of activity in the prominence where the tornado develops. Tornado-like rotations along the side of the prominence start after the second flare. The prominence cavity expands with acceleration of tornado motion after the third flare. Flares in the neighbouring active region may have affected the cavity prominence system and triggered the solar tornado. A plausible mechanism is that the active-region coronal field contracted by the `Hudson effect' due to the loss of magnetic energy as flares. Subsequently the cavity expanded by its magnetic pressure to fill the surrounding low corona. We suggest that the tornado is the dynamical response of the helical prominence field to the cavity expansion.
A precise knowledge of the surface structure of sunspots is essential to construct adequate input models for helioseismic inversion tools. We summarize our recent findings about the velocity and magnetic field in and around sunspots using HINODE observation. To this end we quantize the horizontal and vertical component of the penumbral velocity field at different levels of precision and study the moat flow around sunspot. Furthermore, we find that a significant amount of the penumbral magnetic fields return below the surface within the penumbra. Finally, we explain why the related opposite polarity signals remain hidden in magnetograms constructed from measurements with limited spectral resolution.
Prospects for future supernova surveys are discussed, focusing on the ESA Euclid mission and the European Extremely Large Telescope(E-ELT), both expected to be in operation around the turn of the decade. Euclid is a 1.2m space survey telescope that will operate at visible and near-infrared wavelengths, and has the potential to find and obtain multi-band lightcurves for thousands of distant supernovae. The E-ELT is a planned general-purpose ground-based 40m-class optical-IR telescope with adaptive optics built in, which will be capable of obtaining spectra of Type Ia supernovae to redshifts of at least four. The contribution to supernova cosmology with these facilities will be discussed in the context of other future supernova programs such as those proposed for DES, JWST, LSST and WFIRST.
Growing neutrino quintessence addresses the "why now" problem of dark energy by assuming that the neutrinos are coupled to the dark energy scalar field. The coupling mediates an attractive force between the neutrinos leading to the formation of large neutrino lumps. This work proposes an effective, simplified description of the subsequent cosmological dynamics. We treat neutrino lumps as effective particles and investigate their properties and mutual interactions. The neutrino lump fluid behaves as cold dark matter coupled to dark energy. The methods developed here may find wider applications for fluids of composite objects.
Pulse-pileup affects most photon counting systems and occurs when photon detections occur faster than the detector's registration and recovery time. At high input rates, shaped pulses interfere and the source spectrum, as well as intensity information, get distorted. For instruments using bipolar pulse shaping there are two aspects to consider: `peak' and `tail' pileup effects, which raise and lower the measured energy, respectively. Peak effects have been extensively modeled in the past. Tail effects have garnered less attention due to the increased complexity: bipolar tails mean the tail pulse-height measurement depends on events in more than one time interval. We leverage previous work to derive an accurate, semi-analytical prediction for peak and tail pileup, up to high orders. We use the true pulse shape from the detectors of the Fermi Gamma-ray Burst Monitor. The measured spectrum is calculated by writing exposure time as a state-space expansion of overlapping pileup states and is valid up to very high rates. This expansion models losses due to fixed and extendable deadtime by averaging overlap configurations. Additionally, the model correctly predicts energy-dependent losses due to tail subtraction (sub-threshold) effects. We discuss pileup losses in terms of the true rate of photon detections versus the recorded count rate.
Measuring the water deuterium fractionation in the inner warm regions of low-mass protostars has so far been hampered by poor angular resolution obtainable with single-dish ground- and space-based telescopes. Observations of water isotopologues using (sub)millimeter wavelength interferometers have the potential to shed light on this matter. Observations toward IRAS 16293-2422 of the 5(3,2)-4(4,1) transition of H2-18O at 692.07914 GHz from Atacama Large Millimeter/submillimeter Array (ALMA) as well as the 3(1,3)-2(2,0) of H2-18O at 203.40752 GHz and the 3(1,2)-2(2,1) transition of HDO at 225.89672 GHz from the Submillimeter Array (SMA) are presented. The 692 GHz H2-18O line is seen toward both components of the binary protostar. Toward one of the components, "source B", the line is seen in absorption toward the continuum, slightly red-shifted from the systemic velocity, whereas emission is seen off-source at the systemic velocity. Toward the other component, "source A", the two HDO and H2-18O lines are detected as well with the SMA. From the H2-18O transitions the excitation temperature is estimated at 124 +/- 12 K. The calculated HDO/H2O ratio is (9.2 +/- 2.6)*10^(-4) - significantly lower than previous estimates in the warm gas close to the source. It is also lower by a factor of ~5 than the ratio deduced in the outer envelope. Our observations reveal the physical and chemical structure of water vapor close to the protostars on solar-system scales. The red-shifted absorption detected toward source B is indicative of infall. The excitation temperature is consistent with the picture of water ice evaporation close to the protostar. The low HDO/H2O ratio deduced here suggests that the differences between the inner regions of the protostars and the Earth's oceans and comets are smaller than previously thought.
While tens or hundreds of stellar-remnant black holes are expected to form in globular star clusters, it is still unclear how many of those will be retained upon formation, and how many will be ejected through subsequent dynamical interactions. No such black holes have been found in any Milky Way globular cluster until the recent discovery of stellar-mass black holes in the globular cluster M22 (NGC 6656) with now an estimated population of 5-100 black holes. We present a direct N-body model of a star cluster of the same absolute and dynamical age as M22. Imposing an initial retention fraction of approx. 10% for black holes, 16 stellar-remnant black holes are retained at a cluster age of 12 Gyr, in agreement with the estimate for M22. Of those 16 BHs, two are in a binary system with a main sequence star each while also one pure black hole binary is present. We argue that multiple black holes can be present in any Milky Way cluster with an extended core radius, such as M22 or the model presented here.
One dimensional versions of cosmological N-body simulations have been shown to share many qualitative behaviours of the three dimensional problem. They can resolve a large range of time and length scales, and admit exact numerical integration. We use such models to study how non-linear clustering depends on initial conditions and cosmology. More specifically, we consider a family of models which, like the 3D EdS model, lead for power-law initial conditions to self-similar clustering characterized in the strongly non-linear regime by power-law behaviour of the two point correlation function. We study how the corresponding exponent \gamma depends on the initial conditions, characterized by the exponent n of the power spectrum of initial fluctuations, and on a single parameter \kappa controlling the rate of expansion. The space of initial conditions/cosmology divides very clearly into two parts: (1) a region in which \gamma depends strongly on both n and \kappa and where it agrees very well with a simple generalisation of the so-called stable clustering hypothesis in three dimensions, and (2) a region in which \gamma is more or less independent of both the spectrum and the expansion of the universe. We explain the observed location of the boundary in (n, \kappa) space dividing the "stable clustering" region from the "universal" region. We compare and contrast our findings to results in three dimensions, and discuss in particular the light they may throw on the question of "universality" of non-linear clustering in this context.
Determining fundamental properties of stars through stellar modeling has improved substantially due to recent advances in asteroseismology. Thanks to the unprecedented data quality obtained by space missions, particularly CoRoT and Kepler, invaluable information is extracted from the high-precision stellar oscillation frequencies, which provide very strong constraints on possible stellar models for a given set of classical observations. In this work, we have characterized two relatively faint stars, KIC10920273 and KIC11395018, using oscillation data from Kepler photometry and atmospheric constraints from ground-based spectroscopy. Both stars have very similar atmospheric properties; however, using the individual frequencies extracted from the Kepler data, we have determined quite distinct global properties, with increased precision compared to that of earlier results. We found that both stars have left the main sequence and characterized them as follows: KIC10920273 is a one-solar-mass star (M=1.00 +/- 0.04 M_sun), but much older than our Sun (t=7.12 +/- 0.47 Gyr), while KIC11395018 is significantly more massive than the Sun (M=1.27 +/- 0.04 M_sun) with an age close to that of the Sun (t=4.57 +/- 0.23 Gyr). We confirm that the high lithium abundance reported for these stars should not be considered to represent young ages, as we precisely determined them to be evolved subgiants. We discuss the use of surface lithium abundance, rotation and activity relations as potential age diagnostics.
We explore a cosmological model composed by a dark matter fluid interacting with a dark energy fluid. The interaction term has the non-linear "lambda * rho_m^alpha * rho_e^beta" form, where rho_m and rho_e are the energy densities of the dark matter and dark energy, respectively. The parameters alpha and beta in principle are not constraint to take any particular values. We perform an analytical study of the evolution equations, finding the fixed points and their stability properties in order to characterize suitable physical regions in the space of the dark matter and dark energy densities. The constants (lambda, alpha, beta) as well as (w_m, w_e) of the EoS of dark matter and dark energy respectively were estimated using the cosmological observations of the type Ia supernovae data set and the Hubble parameter H(z) at different redshift. We found that the best fit to data is for a model with a phantom dark energy interacting with a warm dark matter, where the energy transfer comes from the dark energy to the dark matter and with an interacting term of the simple form "rho_m * rho_e". This result is consistent with stable solutions of the dynamical system analysis.
We present Herschel SPIRE FTS spectroscopy of the nearby luminous infrared galaxy NGC 6240. In total 20 lines are detected, including CO J=4-3 through J=13-12, 6 H2O rotational lines, and [CI] and [NII] fine-structure lines. The CO to continuum luminosity ratio is 10 times higher in NGC 6240 than Mrk 231. Although the CO ladders of NGC 6240 and Mrk 231 are very similar, UV and/or X-ray irradiation are unlikely to be responsible for the excitation of the gas in NGC 6240. We applied both C and J shock models to the H2 v=1-0 S(1) and v=2-1 S(1) lines and the CO rotational ladder. The CO ladder is best reproduced by a model with shock velocity v_s=10 km s^-1 and a pre-shock density n_H=5 * 10^4 cm^-3. We find that the solution best fitting the H2 lines is degenerate: The shock velocities and number densities range between v_s = 17 - 47 km s^-1 and n_H=10^7 - 5 * 10^4 cm^-3, respectively. The H2 lines thus need a much more powerful shock than the CO lines. We deduce that most of the gas is currently moderately stirred up by slow (10 km s^-1) shocks while only a small fraction (< 1 percent) of the ISM is exposed to the high velocity shocks. This implies that the gas is rapidly loosing its highly turbulent motions. We argue that a high CO line-to-continuum ratio is a key diagnostic for the presence of shocks.
Proton captures on Mg isotopes play an important role in the Mg-Al cycle active in stellar H-burning regions. In particular, low-energy nuclear resonances in the $^{25}$Mg(p,$\gamma$)$^{26}$Al reaction affect the production of radioactive $^{26}$Al$^{gs}$ as well as the resulting Mg/Al abundance ratio. Reliable estimations of these quantities require precise measurements of the strengths of low-energy resonances. Based on a new experimental study performed at LUNA, we provide revised rates of the $^{25}$Mg(p,$\gamma$)$^{26}$Al$^{gs}$ and the $^{25}$Mg(p,$\gamma$)$^{26}$Al$^{m}$ reactions with corresponding uncertainties. In the temperature range 50 to 150 MK, the new recommended rate of the $^{26}$Al$^{m}$ production is up to 5 times higher than previously assumed. In addition, at T$=100$ MK, the revised total reaction rate is a factor of 2 higher. Note that this is the range of temperature at which the Mg-Al cycle operates in an H-burning zone. The effects of this revision are discussed. Due to the significantly larger $^{25}$Mg(p,$\gamma$)$^{26}$Al$^{m}$ rate, the estimated production of $^{26}$Al$^{gs}$ in H-burning regions is less efficient than previously obtained. As a result, the new rates should imply a smaller contribution from Wolf-Rayet stars to the galactic $^{26}$Al budget. Similarly, we show that the AGB extra-mixing scenario does not appear able to explain the most extreme values of $^{26}$Al/$^{27}$Al, i.e. $>10^{-2}$, found in some O-rich presolar grains. Finally, the substantial increase of the total reaction rate makes the hypothesis of a self-pollution by massive AGBs a more robust explanation for the Mg-Al anticorrelation observed in Globular-Cluster stars.
The first deep blank-field 450um map (1-sigma~1.3mJy) from the SCUBA-2 Cosmology Legacy Survey (S2CLS), conducted with the James Clerk Maxwell Telescope (JCMT) is presented. Our map covers 140 arcmin^2 of the COSMOS field, in the footprint of the HST CANDELS area. Using 60 submillimetre galaxies (SMGs) detected at >3.75-sigma, we evaluate the number counts of 450um-selected galaxies with flux densities S_450>5mJy. The 8-arcsec JCMT beam and high sensitivity of SCUBA-2 now make it possible to directly resolve a larger fraction of the cosmic infrared background (CIB, peaking at ~200um) into the individual galaxies responsible for its emission than has previously been possible at this wavelength. At S_450>5mJy we resolve (7.4[+/-]0.7)x10^-2 MJy/sr of the CIB at 450um (equivalent to 16[+/-]7% of the absolute brightness measured by COBE at this wavelength) into point sources. A further ~40% of the CIB can be recovered through a statistical stack of 24um emitters in this field, indicating that the majority (~60%) of the CIB at 450um is emitted by galaxies with S_450>2mJy. The average redshift of 450um emitters identified with an optical/near-infrared counterpart is estimated to be <z>=1.3, implying that the galaxies in the sample are in the ultraluminous class (L_IR~1.1x10^12 L_sun). If the galaxies contributing to the statistical stack lie at similar redshifts, then the majority of the CIB at 450um is emitted by galaxies in the LIRG class with L_IR>3.6x10^11 L_sun.
In the present work, we analyze the evolution of the scalar and tensorial perturbations and the quantities relevant for the physical description of the Universe, as the density contrast of the scalar perturbations and the gravitational waves energy density during the Bose-Einstein condensation of dark matter. The behavior of these parameters during the Bose-Einstein phase transition of dark matter is analyzed in details. To study the cosmological dynamics and evolution of scalar and tensorial perturbations in a Universe with and without cosmological constant we use both analytical and numerical methods. The Bose-Einstein phase transition modifies the evolution of gravitational waves of cosmological origin, as well as the process of large-scale structure formation.
Electromagnetic (EM) observations of gravitational-wave (GW) sources would bring unique insights into a source which are not available from either channel alone. However EM followup of GW events presents new challenges. GW events will have large sky error regions, on the order of 10-100 square degrees, which can be made up of many disjoint patches. When searching such large areas there is potential contamination by EM transients unrelated to the GW event. Furthermore, the characteristics of possible EM counterparts to GW events are also uncertain. It is therefore desirable to be able to assess the statistical significance of a candidate EM counterpart, which can only be done by performing background studies of large data sets. Current image processing pipelines such as that used by ROTSE are not usually optimised for large-scale processing. We have automated the ROTSE image analysis, and supplemented it with a post-processing unit for candidate validation and classification. We also propose a simple ad hoc statistic for ranking candidates as more likely to be associated with the GW trigger. We demonstrate the performance of the automated pipeline and ranking statistic using archival ROTSE data. EM candidates from a randomly selected set of images are compared to a background estimated from analysis of 102 additional sets of archival images. The pipeline's detection efficiency is computed empirically by re-analysis of the images after adding simulated optical transients that follow typical light curves for gamma-ray burst afterglows and kilonovae. We show that the automated pipeline rejects most background events and is sensitive to simulated transients to limiting magnitudes consistent with the limiting magnitude of the images.
The 3-D and kinematic structure of the Eskimo nebula, NGC 2392, has been notoriously difficult to interpret in detail given its complex morphology, multiple kinematic components and its nearly pole-on orientation along the line of sight. We present a comprehensive, spatially resolved, high resolution, long-slit spectroscopic mapping of the Eskimo planetary nebula. The data consist of 21 spatially resolved, long-slit echelle spectra tightly spaced over the Eskimo and along its bipolar jets. This data set allows us to construct a velocity-resolved [NII] channel map of the nebula with a resolution of 10 km/s that disentangles the different kinematic components of the nebula. The spectroscopic information is combined with HST images to construct a detailed three dimensional morpho-kinematic model of the Eskimo using the code SHAPE. With this model we demonstrate that the Eskimo is a close analog to the Saturn and the Cat's Eye nebulae, but rotated 90 degrees to the line of sight. Furthermore, we show that the main characteristics of our model apply to the general properties of the group of elliptical planetary nebulae with ansae or FLIERS, once the orientation is considered. We conclude that these kind of nebulae belongs to a class with a complex common evolutionary sequence of events.
Recent observations of the cosmic microwave background (CMB) at smallest angular scales and updated abundances of primordial elements, indicate an increase of the energy density and the helium-4 abundance with respect to standard big bang nucleosynthesis with three neutrino flavour. This calls for a reanalysis of the observational bounds on neutrino chemical potentials, which encode the number asymmetry between cosmic neutrinos and anti-neutrinos and thus measures the lepton asymmetry of the Universe. We compare recent data with a big bang nucleosynthesis code, assuming neutrino flavour equilibration via neutrino oscillations before the onset of big bang nucleosynthesis. We find a slight preference for negative neutrino chemical potentials, which would imply an excess of anti-neutrinos and thus a negative lepton number of the Universe. This lepton asymmetry could exceed the baryon asymmetry by orders of magnitude.
We present a multi-wavelength study of the emission-line nebulae located southeast of the nucleus of M87, the central dominant galaxy of the Virgo Cluster. We report the detection of far-infrared (FIR) [CII] line emission from the nebulae using observations made with Herschel PACS. The infrared line emission is extended and cospatial with optical H{\alpha}+[NII], far-ultraviolet CIV lines, and soft X-ray emission. The filamentary nebulae evidently contain multi-phase material spanning a temperature range of at least 5 orders of magnitude, from ~100 K to ~10^7 K. This material has most likely been uplifted by the AGN from the center of M87. The thermal pressure of the 10^4 K phase appears to be significantly lower than that of the surrounding hot intra-cluster medium (ICM) indicating the presence of additional turbulent and magnetic pressure in the filaments. If the turbulence in the filaments is subsonic then the magnetic field strength required to balance the pressure of the surrounding ICM is B~30-70 {\mu}G. The spectral properties of the soft X-ray emission from the filaments indicate that it is due to thermal plasma with kT~0.5-1 keV, which is cooling by mixing with the cold gas and/or radiatively. Charge exchange can be ruled out as a significant source of soft X-rays. Both cooling and mixing scenarios predict gas with a range of temperatures. This is at first glance inconsistent with the apparent lack of X-ray emitting gas with kT<0.5 keV. However, we show that the missing very soft X-ray emission could be absorbed by the cold gas in the filaments with an average absorption column density of ~10^21 cm^-2, providing a natural explanation for the apparent temperature floor to the X-ray emission at kT~0.5 keV. The FIR through ultra-violet line emission is most likely primarily powered by the ICM particles penetrating the cold gas following a shearing induced mixing process.
Analysis of galaxies with overlapping images offers a direct way to probe the distribution of dust extinction and its effects on the background light. We present a catalog of 1990 such galaxy pairs selected from the Sloan Digital Sky Survey (SDSS) by volunteers of the Galaxy Zoo project. We highlight subsamples which are particularly useful for retrieving such properties of the dust distribution as UV extinction, the extent perpendicular to the disk plane, and extinction in the inner parts of disks. The sample spans wide ranges of morphology and surface brightness, opening up the possibility of using this technique to address systematic changes in dust extinction or distribution with galaxy type. This sample will form the basis for forthcoming work on the ranges of dust distributions in local disk galaxies, both for their astrophysical implications and as the low-redshift part of a study of the evolution of dust properties. Separate lists and figures show deep overlaps, where the inner regions of the foreground galaxy are backlit, and the relatively small number of previously-known overlapping pairs outside the SDSS DR7 sky coverage.
1.5D Particle-In-Cell simulations of a hot, low density electron beam injected into magnetized, maxwellian plasma were used to further explore the alternative non-gyrotropic beam driven electromagnetic emission mechanism, first studied in Tsiklauri (2011). Variation of beam injection angle and background density gradient showed that the emission process is caused by the perpendicular component of the beam injection current, whereas the parallel component only produces Langmuir waves, which play no role in the generation of EM waves in our mechanism. Particular emphasis was put on the case, where the beam is injected perpendicularly to the background magnetic field, as this turned off any electrostatic wave generation along the field and left a purely electromagnetic signal in the perpendicular components. The simulations establish the following key findings: i) Initially waves at a few w_ce/gamma are excited, mode converted and emitted at w_pe ii) The emission intensity along the beam axis is proportional to the respective component of the kinetic energy of the beam; iii) The frequency of the escaping EM emission is independent of the injection angle; iv) A stronger background density gradient causes earlier emission; v) The beam electron distribution function in phase space shows harmonic oscillation in the perpendicular components at the relativistic gyrofrequency; vi) The requirement for cyclotron maser emission, df/dv_perp > 0, is fulfilled; vii) The degree of linear polarization of the emission is strongly dependent on the beam injection angle; viii) The generated electromagnetic emission is left-hand elliptically polarized as the pitch angle tends to 90 deg; ix) The generated electromagnetic energy is of the order of 0.1% of the initial beam kinetic energy.
A beam of super-thermal, hot electrons was injected into maxwellian plasma with a density gradient along a magnetic field line. 1.5D particle-in-cell simulations were carried out which established that the EM emission is produced by the perpendicular component of the beam injection momentum. The beam has a positive slope in the distribution function in perpendicular momentum phase space, which is the characteristic feature of a cyclotron maser. The cyclotron maser in the overdense plasma generates emission at the electron cyclotron frequency. The frequencies of generated waves were too low to propagate away from the injection region, hence the wavelet transform shows a pulsating wave generation and decay process. The intensity pulsation frequency is twice the relativistic cyclotron frequency. Eventually, a stable wave packet formed and could mode couple on the density gradient to reach frequencies of the order of the plasma frequency, that allowed for propagation. The emitted wave is likely to be a z-mode wave. The total electromagnetic energy generated is of the order of 0.1% of the initial beam kinetic energy. The proposed mechanism is of relevance to solar type III radio bursts, as well as other situations, when the injected electron beam has a non-zero perpendicular momentum, e.g. magnetron.
We employ the superpotential technique for the reconstruction of cosmological models with a non-minimally coupled scalar field evolving on a spatially flat Friedmann-Robertson-Walker background. The key point in this method is that the Hubble parameter is considered as a function of the scalar field and this allows one to reconstruct the scalar field potential and determine the dynamics of the field itself, without a priori fixing the Hubble parameter as a function of time or of the scale factor. The scalar field potentials which lead to de Sitter or asymptotic de Sitter solutions, and those which reproduce the cosmological evolution given by Einstein-Hilbert action plus a barotropic perfect fluid, have been obtained.
We show that the smooth hybrid inflation is naturally realized in a framework of supersymmetric axion model. Identifying the Peccei-Quinn scalar fields as a part of the infaton sector, successful inflation takes place reproducing the amplitude and spectral index of the curvature perturbation observed by WMAP. A relatively large axion isocurvature perturbation and its non-Gaussianity are predicted in our model. The saxion coherent oscillation has a large amplitude and dominates the Universe. The subsequent decay of the saxion produces huge amount of entropy, which dilutes unwanted relics. Winos, the lightest supersymmetric particles in this scenario, are produced non-thermally in the decay and account for dark matter.
New tests are proposed to constrain possible deviations from local Lorentz invariance and local position invariance in the gravity sector. By using precise timing results of two binary pulsars, i.e., PSRs J1012+5307 and J1738+0333, we are able to constrain (strong-field) parametrized post-Newtonian parameters $\hat{\alpha}_1$, $\hat{\alpha}_2$, $\hat{\xi}$ to high precision, among which, $|\hat{\xi}| < 3.1\times10^{-4}$ (95% C.L.) is reported here for the first time.
We discuss status of the singularity problem in General Relativity and argue that the requirement that a physical solution must be completely free of singularities may be too strong. As an example, we consider properties of the integrable singularities and show that they represent light horizons separating T-regions of black and white holes. Connecting an astrophysical black hole to a white hole, they lead to a natural mechanism of generating new universes. Under favorable conditions the new universes will also contain black holes which, in their turn, will give rise to another generation of universes. In this case the cosmological evolutionary tree will continue to grow to form the "hyperverse". This scenario essentially differs from other known mechanisms, such as bounce, birth from "nothing", baby-universe scenario, etc.
In the absence of symmetry assumptions most numerical relativity simulations adopt Cartesian coordinates. While Cartesian coordinates have some desirable properties, spherical polar coordinates appear better suited for certain applications, including gravitational collapse and supernova simulations. Development of numerical relativity codes in spherical polar coordinates has been hampered by the need to handle the coordinate singularities at the origin and on the axis, for example by careful regularization of the appropriate variables. Assuming spherical symmetry and adopting a covariant version of the BSSN equations, Montero and Cordero-Carri\'on recently demonstrated that such a regularization is not necessary when a partially implicit Runge-Kutta (PIRK) method is used for the time evolution of the gravitational fields. Here we report on an implementation of the BSSN equations in spherical polar coordinates without any symmetry assumptions. Using a PIRK method we obtain stable simulations in three spatial dimensions without the need to regularize the origin or the axis. We perform and discuss a number of tests to assess the stability, accuracy and convergence of the code, namely weak gravitational waves, "hydro-without-hydro" evolutions of spherical and rotating relativistic stars in equilibrium, and single black holes.
The distribution function $f(\psi)$ of magnetic flux $\psi$ in plasmoids formed in high-Lundquist-number current sheets is studied by means of an analytic phenomenological model and direct numerical simulations. The distribution function is shown to follow a power law $f(\psi)\sim\psi^{-1}$, which differs from other recent theoretical predictions. Physical explanations are given for the discrepant predictions of other theoretical models.
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In the past, the outer Solar System likely could have more planets than now. Using the new relations, we have found the orbital and physical characteristics of the icy giant explanet, which orbited the Sun about in the halfway between Saturn and Uranus. Validity of the obtained results is supported by the feasibility of these relations to other objects of the outer Solar System. Possible connection of the existing now mysterious objects of the outer Solar System such as the Saturn rings and the irregular moons Triton and Phoebe with this destroyed planet is briefly discussed.
Interacting galaxies often have complexes of hundreds of young stellar clusters of individual masses ~ 10^{4-6} Msun in regions that are a few hundred parsecs across. These cluster complexes interact dynamically, and their coalescence is a candidate for the origin of some ultracompact dwarf galaxies (UCDs). Individual clusters with short relaxation times are candidates for the production of intermediate-mass black holes of a few hundred solar masses, via runaway stellar collisions prior to the first supernovae in a cluster. It is therefore possible that a cluster complex hosts multiple intermediate-mass black holes that may be ejected from their individual clusters due to mergers or binary processes, but bound to the complex as a whole. Here we explore the dynamical interaction between initially free-flying massive black holes and clusters in an evolving cluster complex. We find that, after hitting some clusters, it is plausible that the massive black hole will be captured in an ultracompact dwarf forming near the center of the complex. In the process, the hole typically triggers electromagnetic flares via stellar disruptions, and is also likely to be a prominent source of gravitational radiation for the advanced ground-based detectors LIGO and VIRGO. We also discuss other implications of this scenario, notably that the central black hole could be considerably larger than expected in other formation scenarios for ultracompact dwarfs.
While standard solar model (SSM) predictions depend on approximately 20 input parameters, SSM neutrino flux predictions are strongly correlated with a single model output parameter, the core temperature $T_c$. Consequently, one can extract physics from solar neutrino flux measurements while minimizing the consequences of SSM uncertainties, by studying flux ratios with appropriate power-law weightings tuned to cancel this $T_c$ dependence. We re-examine an idea for constraining the primordial C+N content of the solar core from a ratio of CN-cycle $^{15}$O to pp-chain $^8$B neutrino fluxes, showing that nonnuclear SSM uncertainties in the ratio are small and effectively governed by a single parameter, the diffusion coefficient. We point out that measurements of both CN-I cycle neutrino branches -- $^{15}$O and $^{13}$N $\beta$-decay -- could in principle lead to separate determinations of the core C and N abundances, due to out-of-equilibrium CN-cycle burning in the cooler outer layers of the solar core. Finally, we show that the strategy of constructing "minimum uncertainty" neutrino flux ratios can also test other properties of the SSM. In particular, we demonstrate that a weighted ratio of $^7$Be and $^8$B fluxes constrains a product of S-factors to the same precision currently possible with laboratory data.
We report low resolution near infrared spectroscopic observations of the eruptive star FU Orionis using the Integral Field Spectrograph Project 1640 installed at the Palomar Hale telescope. This work focuses on elucidating the nature of the faint source, located 0.5" south of FU Ori, and identified in 2003 as FU Ori S. We first use our observations in conjunction with published data to demonstrate that the two stars are indeed physically associated and form a true binary pair. We then proceed to extract J and H band spectro-photometry using the damped LOCI algorithm, a reduction method tailored for high contrast science with IFS. This is the first communication reporting the high accuracy of this technique, pioneered by the Project 1640 team, on a faint astronomical source. We use our low resolution near infrared spectrum in conjunction with 10.2 micron interferometric data to constrain the infrared excess of FU Ori S. We then focus on estimating the bulk physical properties of FU Ori S. Our models lead to estimates of an object heavily reddened, A_V =8-12, with an effective temperature of ~ 4000-6500 K . Finally we put these results in the context of the FU Ori N-S system and argue that our analysis provides evidence that FU Ori S might be the more massive component of this binary system
We present ALMA continuum and spectral line observations of the young Brown Dwarf rho-Oph 102 at about 0.89 mm and 3.2 mm. We detect dust emission from the disk at these wavelengths and derive an upper limit on the radius of the dusty disk of ~ 40 AU. The derived variation of the dust opacity with frequency in the mm provides evidence for the presence of mm-sized grains in the disk outer regions. This result demonstrates that mm-grains are found even in the low density environments of Brown Dwarf disks and challenges our current understanding of dust evolution in disks. The CO map at 345 GHz clearly reveals molecular gas emission at the location of the Brown Dwarf, indicating a gas-rich disk as typically found for disks surrounding young pre-Main Sequence stars. We derive a disk mass of ~ 0.3-1% of the mass of the central Brown Dwarf, similar to the typical values found for disks around more massive young stars.
The accuracy of the measurements of some astrophysical dynamical systems allows to constrain the existence of incredibly small gravitational perturbations. In particular, the internal Solar System dynamics (planets, Earth-Moon) opens up the possibility, for the first time, to prove the abundance, mass and size, of dark sub-structures at the Earth vicinity. We find that adopting the standard dark matter density, its local distribution can be composed by sub-solar mass halos with no currently measurable dynamical consequences, regardless of the mini-halo fraction. On the other hand, it is possible to exclude the presence of dark streams with linear mass densities higher than $\lambda_{\rm st}> 10^{-10} \Msun/\AU$ (about the Earth mass spread along the diameter of the SS up to the Kuiper belt). In addition, we review the dynamics of wide binaries inside the dwarf spheroidal galaxies in the MW. The dynamics of such kind of binaries seem to be compatible with the presence of a huge fraction of dark sub-structure, thus their existence is not a sharp discriminant of the dark matter hypothesis as been claimed before. However, there are regimes where the constraints from different astrophysical systems may reveal the sub-structure mass function cut-off scale.
We present results from a study of optically emitting Supernova Remnants (SNRs) in six nearby galaxies (NGC 2403, NGC 3077, NGC 4214, NGC 4395, NGC 4449 and NGC 5204) based on deep narrow band H{\alpha} and [SII] images as well as spectroscopic observations. The SNR classification was based on the detected sources that fulfill the well-established emission line flux criterion of [SII]/H{\alpha} > 0.4. This study revealed ~400 photometric SNRs down to a limiting H{\alpha} flux of 10^(-15) erg sec^(-1) cm^(-2). Spectroscopic observations confirmed the shock-excited nature of 56 out of the 96 sources with ([SII]/H{\alpha})$_{phot}$> 0.3 (our limit for an SNR classification) for which we obtained spectra. 11 more sources were spectroscopically identified as SNRs although their photometric [SII]/H{\alpha} ratio was below 0.3. We discuss the properties of the optically-detected SNRs in our sample for different types of galaxies and hence different environments, in order to address their connection with the surrounding interstellar medium. We find that there is a difference in [NII]/H{\alpha} line ratios of the SNR populations between different types of galaxies which indicates that this happens due to metallicity. We cross-correlate parameters of the optically detected SNRs ([SII]/H{\alpha} ratio, luminosity) with parameters of coincident X- ray emitting SNRs, resulted from our previous studies in the same sample of galaxies, in order to understand their evolution and investigate possible selection effects. We do not find a correlation between their H{\alpha} and X-ray luminosities, which we attribute to the presence of material in a wide range of temperatures. We also find evidence for a linear relation between the number of luminous optical SNRs (10^(37) erg sec^(-1)) and SFR in our sample of galaxies.
Due to the exquisite photometric precision, transiting exoplanet discoveries from the Kepler mission are enabling several new techniques of confirmation and characterization. One of these newly accessible techniques analyzes the phase variations of planets as they orbit their stars. The predicted phase variation for multi-planet systems can become rapidly complicated and depends upon the period, radius, and albedo distributions for planets in the system. Here we describe the confusion which may occur due to short-period terrestrial planets and/or non-transiting planets in a system, which can add high-frequency correlated noise or low-frequency trends to the data stream. We describe these sources of ambiguity with several examples, including that of our Solar System. We further show how decoupling of these signals may be achieved with application to the Kepler-20 and Kepler-33 multi-planet systems.
We investigate the chemical properties of low-z QSOs, using archival UV spectra obtained with the HST and IUE for a sample of 70 Palomar-Green QSOs at z < 0.5. By utilizing the flux ratio of UV emission lines (i.e., NV /CIV, (SiIV+OIV])/CIV, and NV/HeII) as metallicity indicators, we compare broad-line region (BLR) gas metallicity with AGN properties, i.e., black hole mass, luminosity, and Eddington ratio. We find that BLR metallicity correlates with Eddington ratio while the dependency on black hole mass is much weaker. Although these trends of low-z AGNs appear to be different from those of high-z QSOs, the difference between low-z and high-z samples is partly caused by the limited dynamical range of the samples. We find that metal enrichment at the center of galaxies is closely connected to the accretion activity of black holes and that the scatter of metallicity correlations with black hole mass increases over cosmic time.
We report the results of high spatial and spectral resolution integral-field spectroscopy of the central ~3 x 3 arcsec^2 of the active galaxy NGC 1275 (Perseus A), based on observations with the Near-infrared Integral Field Spectrograph (NIFS) and the ALTAIR adaptive-optics system on the Gemini North telescope. The circum-nuclear disc in the inner R~50 pc of NGC 1275 is seen in both the H2 and [FeII] lines. The disc is interpreted as the outer part of a collisionally-excited turbulent accretion disc. The kinematic major axis of the disc at a position angle of 68 deg is oriented perpendicular to the radio jet. A streamer-like feature to the south-west of the disc, detected in H2 but not in [FeII], is discussed as one of possibly several molecular streamers, presumably falling into the nuclear region. Indications of an ionization structure within the disc are deduced from the HeI and Br gamma emission lines, which may partially originate from the inner portions of the accretion disc. The kinematics of these two lines agrees with the signature of the circum-nuclear disc, but both lines display a larger central velocity dispersion than the H2 line. The rovibrational H2 transitions from the core of NGC 1275 are indicative of thermal excitation caused by shocks and agree with excitation temperatures of ~1360 and ~4290 K for the lower- and higher-energy H2 transitions, respectively. The data suggest X-ray heating as the dominant excitation mechanism of [FeII] emission in the core, while fast shocks are a possible alternative. The [FeII] lines indicate an electron density of ~4000 cm^{-3}. The H2 disc is modelled using simulated NIFS data cubes of H2 emission from inclined discs in Keplerian rotation around a central mass. Assuming a disc inclination of 45 deg +/- 10 deg, the best-fitting models imply a central mass of (8^{+7}_{-2}) x 10^8 Msun. (abridged)
Increasing interest in astronomical applications of non-linear curvature
wavefront sensors for turbulence detection and correction makes it important to
understand how best to handle the data they produce, particularly at low light
levels. Algorithms for wavefront phase-retrieval from a four-plane curvature
wavefront sensor are developed and compared, with a view to their use for low
order phase compensation in instruments combining adaptive optics and Lucky
Imaging. The convergence speed and quality of iterative algorithms is compared
to their step-size and techniques for phase retrieval at low photon counts are
explored.
Computer simulations show that at low light levels, preprocessing by
convolution of the measured signal with a gaussian function can reduce by an
order of magnitude the photon flux required for accurate phase retrieval of
low-order errors. This facilitates wavefront correction on large telescopes
with very faint reference stars.
Bars play a major role in driving the evolution of disk galaxies and in shaping their present properties. They cause angular momentum to be redistributed within the galaxy, emitted mainly from (near-)resonant material at the inner Lindblad resonance of the bar, and absorbed mainly by (near-)resonant material in the spheroid (i.e., the halo and, whenever relevant, the bulge) and in the outer disk. Spheroids delay and slow down the initial growth of the bar they host, but, at the later stages of the evolution, they strengthen the bar by absorbing angular momentum. Increased velocity dispersion in the (near-)resonant regions delays bar formation and leads to less strong bars. When bars form they are vertically thin, but soon their inner parts puff up and form what is commonly known as the boxy/peanut bulge. This gives a complex and interesting shape to the bar which explains a number of observations and also argues that the COBE/DIRBE bar and the Long bar in our Galaxy are, respectively, the thin and the thick part of a single bar. The value of the bar pattern speed may be set by optimising the balance between emitters and absorbers, so that a maximum amount of angular momentum is redistributed. As they evolve, bars grow stronger and rotate slower. Bars also redistribute matter within the galaxy, create a disky bulge (pseudo-bulge), increase the disk scale-length and extent and drive substructures such as spirals and rings. They also affect the shape of the inner part of the spheroid, which can evolve from spherical to triaxial.
The accelerated expansion of space during the period of cosmological inflation leads to trans-Planckian issues which need to be addressed. Most importantly, the physical wavelength of fluctuations which are studied at the present time by means of cosmological observations may well originate with a wavelength smaller than the Planck length at the beginning of the inflationary phase. Thus, questions arise as to whether the usual predictions of inflationary cosmology are robust considering our ignorance of physics on trans-Planckian scales, and whether the imprints of Planck-scale physics are at the present time observable. These and other related questions are reviewed in this article.
We follow the formation and evolution of bars in N-body simulations of disc
galaxies with gas and/or a triaxial halo. We find that both the relative gas
fraction and the halo shape play a major role in the formation and evolution of
the bar. In gas-rich simulations, the disc stays near-axisymmetric much longer
than in gas-poor ones, and, when the bar starts growing, it does so at a much
slower rate. Due to these two effects combined, large-scale bars form much
later in gas-rich than in gas-poor discs. This can explain the observation that
bars are in place earlier in massive red disc galaxies than in blue spirals. We
also find that the morphological characteristics in the bar region are strongly
influenced by the gas fraction. In particular, the bar at the end of the
simulation is much weaker in gas-rich cases. In no case did we witness bar
destruction.
Halo triaxiality has a dual influence on bar strength. In the very early
stages of the simulation it induces bar formation to start earlier. On the
other hand, during the later, secular evolution phase, triaxial haloes lead to
considerably less increase of the bar strength than spherical ones. The shape
of the halo evolves considerably with time. The inner halo parts may become
more elongated, or more spherical, depending on the bar strength. The main body
of initially triaxial haloes evolves towards sphericity, but in initially
strongly triaxial cases it stops well short of becoming spherical. Part of the
angular momentum absorbed by the halo generates considerable rotation of the
halo particles that stay located relatively near the disc for long periods of
time. Another part generates halo bulk rotation, which, contrary to that of the
bar, increases with time but stays small.
The effect of our Galaxy's motion through the Cosmic Microwave Background rest frame, which aberrates and Doppler shifts incoming photons measured by current CMB experiments, has been shown to produce mode-mixing in the multipole space temperature coefficients. However, multipole space determinations are subject to many difficulties, and a real-space analysis can provide a straightforward alternative. In this work we describe a numerical method for removing Lorentz- boost effects from real-space temperature maps. We show that to deboost a map so that one can accurately extract the temperature power spectrum requires calculating the boost kernel at a finer pixelization than one might naively expect. In idealized cases that allow for easy comparison to analytic results, we have confirmed that there is indeed mode mixing among the spherical harmonic coefficients of the temperature. We find that using a boost kernel calculated at Nside=8192 leads to a 1% bias in the binned boosted power spectrum at l~2000, while individual Cls exhibit ~5% fluctuations around the binned average. However, this bias is dominated by pixelization effects and not the aberration and Doppler shift of CMB photons that causes the fluctuations. Performing analysis on maps with galactic cuts does not induce any additional error in the boosted, binned power spectra over the full sky analysis. For multipoles that are free of resolution effects, there is no detectable deviation between the binned boosted and unboosted spectra. This result arises because the power spectrum is a slowly varying function of and does not show that, in general, Lorentz boosts can be neglected for other cosmological quantities such as polarization maps or higher-point functions.
We used unprecedentedly large 2D and 3D hybrid (kinetic ions - fluid electrons) simulations of non-relativistic collisionless strong shocks in order to investigate the effects of self-consistently accelerated ions on the overall shock dynamics. The current driven by suprathermal particles streaming ahead of the shock excites modes transverse to the background magnetic field. The Lorentz force induced by these self-amplified fields tends to excavate tubular, underdense, magnetic-field-depleted cavities that are advected with the fluid and perturb the shock surface, triggering downstream turbulent motions. These motions further amplify the magnetic field, up to factors of 50-100 in knot-like structures. Once downstream, the cavities tend to be filled by hot plasma plumes that compress and stretch the magnetic fields in elongated filaments; this effect is particularly evident if the shock propagates parallel to the background field. Highly-magnetized knots and filaments may provide explanations for the rapid X-ray variability observed in RX J1713.7-3946 and for the regular pattern of X-ray bright stripes detected in Tycho's supernova remnant.
On the 40th anniversary of the last human expedition to the Moon, I review the scientific legacy of the Apollo programme and argue that science would benefit from a human return to the Moon.
Neutrinos and gravitational waves are the only direct probes of the inner dynamics of a stellar core collapse. They are also the first signals to arrive from a supernova and, if detected, establish the moment when the shock wave is formed that unbinds the stellar envelope and later initiates the optical display upon reaching the stellar surface with a burst of UV and X-ray photons, the shock breakout (SBO). We discuss how neutrino observations can be used to trigger searches to detect the elusive SBO event. Observation of the SBO would provide several important constraints on progenitor structure and the explosion, including the shock propagation time (the duration between the neutrino burst and SBO), an observable that is important in distinguishing progenitor types. Our estimates suggest that next generation neutrino detectors could exploit the overdensity of nearby SNe to provide several such triggers per decade, more than an order of magnitude improvement over the present.
A preliminary assessment of the in-flight radiometric calibration of the Hinode EUV Imaging Spectrometer (EIS) is presented. This is done with the line ratio technique applied to a wide range of observations of the quiet Sun, active regions and flares from 2006 until 2012. Radiances over the quiet Sun are also considered. The responsivity of the EIS short-wavelength (SW) channel does not show significant degradation, with the exception of its shorter wavelengths. The responsivity of the EIS long-wavelength (LW) channel instead shows an overall degradation with time, with values at the start of the mission already lower by 30% than those measured on the ground. Some departures in the shapes of the ground calibration responsivities are also found. The net effect is that by the beginning of 2010 the responsivity of the LW channel was already a factor of two or more lower than the values measured on the ground. A first-order correction is proposed. With this correction, the main ratios of lines in the two channels become constant to within a relative 20%, and the He II 256 A radiances over the quiet Sun also become constant over time. This correction removes long-standing discrepancies for a number of lines and ions, in particular those involving the strongest Fe X, Fe XIII, Fe XIV, Fe XVII, and Fe XXIV lines, where discrepancies of factors of more than two were found. These results have important implications for various EIS science analyses, in particular for measurements of temperatures, emission measures and elemental abundances.
Centaurus B is a nearby radio galaxy positioned in the Southern hemisphere close to the Galactic plane. Here we present a detailed analysis of about 43 months of accumulated Fermi-LAT data of the gamma-ray counterpart of the source initially reported in the 2nd Fermi-LAT catalog, and of newly acquired Suzaku X-ray data. We confirm its detection at GeV photon energies, and analyze the extension and variability of the gamma-ray source in the LAT dataset, in which it appears as a steady gamma-ray emitter. The X-ray core of Centaurus B is detected as a bright source of a continuum radiation. We do not detect however any diffuse X-ray emission from the known radio lobes, with the provided upper limit only marginally consistent with the previously claimed ASCA flux. Two scenarios that connect the X-ray and gamma-ray properties are considered. In the first one, we assume that the diffuse non-thermal X-ray emission component is not significantly below the derived Suzaku upper limit. In this case, modeling the inverse-Compton emission shows that the observed gamma-ray flux of the source may in principle be produced within the lobes. This association would imply that efficient in-situ acceleration of the radiating electrons is occurring and that the lobes are dominated by the pressure from the relativistic particles. In the second scenario, with the diffuse X-ray emission well below the Suzaku upper limits, the lobes in the system are instead dominated by the magnetic pressure. In this case, the observed gamma-ray flux is not likely to be produced within the lobes, but instead within the nuclear parts of the jet. By means of synchrotron self-Compton modeling we show that this possibility could be consistent with the broad-band data collected for the unresolved core of Centaurus B, including the newly derived Suzaku spectrum.
We measure the clustering of Extremely Red Objects (EROs) in ~8 deg^2 of the NOAO Deep Wide Field Survey Bo\"otes field in order to establish robust links between ERO z~1.2 and local galaxy z<0.1 populations. Three different color selection criteria from the literature are analyzed to assess the consequences of using different criteria for selecting EROs. Specifically, our samples are (R-K_s)>5.0 (28,724 galaxies), (I-K_s)>4.0 (22,451 galaxies) and (I-[3.6])>5.0 (64,370 galaxies). Magnitude-limited samples show the correlation length (r_0) to increase for more luminous EROs, implying a correlation with stellar mass. We can separate star-forming and passive ERO populations using the (K_s-[24]) and ([3.6]-[24]) colors to K_s=18.4 and [3.6]=17.5, respectively. Star-forming and passive EROs in magnitude limited samples have different clustering properties and host dark halo masses, and cannot be simply understood as a single population. Based on the clustering, we find that bright passive EROs are the likely progenitors of >4L^* elliptical galaxies. Bright EROs with ongoing star formation were found to occupy denser environments than star-forming galaxies in the local Universe, making these the likely progenitors of >L^* local ellipticals. This suggests that the progenitors of massive >4L^* local ellipticals had stopped forming stars by z>1.2, but that the progenitors of less massive ellipticals (down to L^*) can still show significant star formation at this epoch.
According to the core accretion theory, circumbinary embryos can form only beyond a critical semimajor axis (CSMA). However, due to the relatively high density of solid materials in the inner disk, significant amount of small planetesimals must exist in the inner zone when embryos were forming outside this CSMA. So embryos migration induced by the planetesimal swarm is possible after the gas disk depletion. Through numerical simulations, we found (i) the scattering-driven inward migration of embryos is robust, planets can form in the habitable zone if we adopt a mass distribution of MMSN-like disk; (ii) the total mass of the planetesimals in the inner region and continuous embryo-embryo scattering are two key factors that cause significant embryo migrations; (iii) the scattering-driven migration of embryos is a natural water-deliver mechanism. We propose that planet detections should focus on the close binary with its habitable zone near CSMA.
We present the results of the deepest search to date for star-forming galaxies beyond a redshift z~8.5 utilizing a new sequence of near-infrared Wide Field Camera 3 images of the Hubble Ultra Deep Field. This `UDF12' campaign completed in September 2012 doubles the earlier exposures with WFC3/IR in this field and quadruples the exposure in the key F105W filter used to locate such distant galaxies. Combined with additional imaging in the F140W filter, the fidelity of high redshift candidates is greatly improved. Using spectral energy distribution fitting techniques on objects selected from a deep multi-band near-infrared stack we find 7 promising z>8.5 candidates. As none of the previously claimed UDF candidates with 8.5<z<10 is confirmed by our deeper multi-band imaging, our campaign has transformed the measured abundance of galaxies in this redshift range. Although we recover the candidate UDFj-39546284 (previously proposed at z=10.3), it is undetected in the newly added F140W image, implying it lies at z=11.9 or is an intense emission line galaxy at z~2.4. Although no physically-plausible model can explain the required line intensity given the lack of Lyman alpha or broad-band UV signal, without an infrared spectrum we cannot rule out an exotic interloper. Regardless, our robust z ~ 8.5 - 10 sample demonstrates a luminosity density that continues the smooth decline observed over 6 < z < 8. Such continuity has important implications for models of cosmic reionization and future searches for z>10 galaxies with JWST.
We present an analysis of new and archival VLA HI observations of a sample of eleven early-type galaxies rich in CO, with detailed comparisons of CO and HI distributions and kinematics. The early-type sample consists of both lenticular and elliptical galaxies in a variety of environments. A range of morphologies and environments were selected in order to give a broader understanding of the origins, distribution, and fate of the cold gas in early-type galaxies. Six of the eleven galaxies in the sample are detected in both HI and CO. The H$_{2}$ to HI mass ratios for this sample range from 0.2-120. The HI morphologies of the sample are consistent with that of recent HI surveys of early-type galaxies which also find a mix of HI morphologies and masses, low HI peak surface densities, and a lack of HI in early-type galaxies which reside in high density environments. The HI-detected galaxies have a wide range of HI masses (1.4$\times10^{6}$ to 1.1$\times10^{10}$ M$_{\odot}$). There does not appear to be any correlation between the HI mass and morphology (E versus S0). When HI is detected, it is centrally peaked - there are no central kpc-scale central HI depressions like those observed for early-type spiral galaxies at similar spatial resolutions and scales. A kinematic comparison between the HI and CO indicates that both cold gas components share the same origin. The primary goal of this and a series of future papers is to better understand the relationship between the atomic and molecular gas in early-type galaxies, and to compare the observed relationships with those of spiral galaxies where this relationship has been studied in depth.
We investigate the nature of tidal effects in compact triple-star systems. The hierarchical structure of a triple system produces tidal forcing at high frequencies unobtainable in binary systems, allowing for the tidal excitation of high frequency p-modes in the stellar components. The tidal forcing exists even for circular, aligned, and synchronized systems. We calculate the magnitude and frequencies of three-body tidal forcing on the central primary star for circular and coplanar orbits, and we estimate the amplitude of the tidally excited oscillation modes. We also calculate the secular orbital changes induced by the tidally excited modes, and show that they can cause significant orbital decay. During certain phases of stellar evolution, the tidal dissipation may be greatly enhanced by resonance locking. We then compare our theory to observations of HD 181068, which is a hierarchical triply eclipsing star system in the Kepler field of view. The observed oscillation frequencies in HD 181068 can be naturally explained by three-body tidal effects. We then compare the observed oscillation amplitudes and phases in HD 181068 to our predictions, finding mostly good agreement. Finally, we discuss the past and future evolution of compact triple systems like HD 181068.
We studied roles of a turbulent resistivity in the core-collapse of a strongly magnetized massive star, carrying out 2D-resistive-MHD simulations. The three cases with different initial strengths of magnetic field and rotation are investigated; 1. strongly magnetized rotating core; 2.moderately magnetized rotating core; 3. very strongly magnetized non-rotating core. In each case, both an ideal-MHD model and resistive-MHD models are computed. As a result of computations, each model shows a matter eruption helped by a magnetic acceleration (and also by a centrifugal acceleration in the rotating cases). We found that a resistivity attenuates the explosion in case~1 and 2, while it enhances the explosion in case~3. We also found that in the rotating cases, main mechanisms for the amplification of a magnetic field in the post-bounce phase are an outward advection of magnetic field and a winding of poloidal magnetic field-lines by differential rotation, which are somewhat dampened down with the presence of a resistivity. Although the magnetorotational instability seems to occur in the rotating models, it will play only a minor role in a magnetic field amplification. Another impact of resistivity is that on the aspect ratio. In the rotating cases, a large aspect ratio of the ejected matters, $> 2.5$, attained in a ideal-MHD model is reduced to some extent in a resistive model. These results indicate that a resistivity possibly plays an important role in the dynamics of strongly magnetized supernovae.
The Apache Point Survey of Transit Lightcurves of Exoplanets (APOSTLE) observed eleven transits of TrES-3b over two years in order to constrain system parameters and look for transit timing and depth variations. We describe an updated analysis protocol for APOSTLE data, including the reduction pipeline, transit model and Markov Chain Monte Carlo analyzer. Our estimates of the system parameters for TrESb are consistent with previous estimates to within the 2\sigma\ confidence level. We improved the errors (by 10--30%) on system parameters like the orbital inclination ($i_{\text{orb}}$), impact parameter (b) and stellar density (\rho$_{\star}$) compared to previous measurements. The near-grazing nature of the system, and incomplete sampling of some transits, limited our ability to place reliable uncertainties on individual transit depths and hence we do not report strong evidence for variability. Our analysis of the transit timing data show no evidence for transit timing variations and our timing measurements are able to rule out Super-Earth and Gas Giant companions in low order mean motion resonance with TrES-3b.
We explore how the co-evolution of massive black holes (MBHs) and galaxies is affected by environmental effects, addressing in particular MBHs hosted in the central galaxies of clusters (we will refer to these galaxies in general as 'CGs'). Recently the sample of MBHs in CGs with dynamically measured masses has increased, and it has been suggested that these MBH masses (M_BH) deviate from the expected correlations with velocity dispersion (sigma) and mass of the bulge (M_bulge) of the host galaxy: MBHs in CGs appear to be `over-massive'. This discrepancy is more pronounced when considering the M_BH-sigma relation than the M_BH-M_bulge one. We show that this behavior stems from a combination of two natural factors, (i) that CGs experience more mergers involving spheroidal galaxies and their MBHs, and (ii) that such mergers are preferentially gas-poor. We use a combination of analytical and semi-analytical models to investigate the MBH-galaxy co-evolution in different environments and find that the combination of these two factors explains the trends observed in current data-sets.
The determination of age is a critical component in the study of a population of stellar clusters. In this letter we present a new absolute age indicator for young massive star clusters based on J-H colour. This novel method identifies clusters as older or younger than 5.7 +/- 0.8 Myr based on the appearance of the first population of red supergiant stars. We test the technique on the stellar cluster population of the nearby spiral galaxy, M83, finding good agreement with the theoretical predictions. The localisation of this technique to the near-IR promises that it may be used well into the future with space-- and ground--based missions optimised for near-IR observations.
We present a high angular resolution map of 850 um continuum emission of the Orion Molecular Cloud-3 (OMC 3) obtained with the Submillimeter Array (SMA); the map is a mosaic of 85 pointings covering an approximate area of 6'.5 x 2'.0 (0.88 x 0.27 pc). We detect 12 spatially resolved continuum sources, each with an H_2 mass between 0.3-5.7 Mo and a projected source size between 1400-8200 AU. All the detected sources are on the filamentary main ridge n_H2>10^6 cm^-3), and analysis based on the Jeans theorem suggests that they are most likely gravitationally unstable. Comparison of multi-wavelength data sets indicates that of the continuum sources, 6/12 (50 %) are associated with molecular outflows, 8/12 (67 %) are associated with infrared sources, and 3/12 (25 %) are associated with ionized jets. The evolutionary status of these sources ranges from prestellar cores to protostar phase, confirming that OMC-3 is an active region with ongoing embedded star-formation. We detect quasi-periodical separations between the OMC-3 sources of ~17"/0.035 pc. This spatial distribution is part of a large hierarchical structure, that also includes fragmentation scales of GMC (~35 pc), large-scale clumps (~1.3 pc), and small-scale clumps (~0.3 pc), suggesting that hierarchical fragmentation operates within the Orion A molecular cloud. The fragmentation spacings are roughly consistent with the thermal fragmentation length in large-scale clumps, while for small-scale cores it is smaller than the local fragmentation length. These smaller spacings observed with the SMA can be explained by either a helical magnetic field, cloud rotation, or/and global filament collapse. Finally, possible evidence for sequential fragmentation is suggested in the northern part of the OMC-3 filament.
Based on high-resolution spectra obtained during gravitational microlensing events we present a detailed elemental abundance analysis of 32 dwarf and subgiant stars in the Galactic bulge. [ABRIDGED], we now have 58 microlensed bulge dwarfs and subgiants that have been homogeneously analysed. The main characteristics of the sample and the findings that can be drawn are: (i) The metallicity distribution (MDF) is wide and spans all metallicities between [Fe/H]=-1.9 to +0.6; (ii) The dip in the MDF around solar metallicity that was apparent in our previous analysis of a smaller sample (26 microlensed stars) is no longer evident; instead it has a complex structure and indications of multiple components are starting to emerge. [ABRIDGED]; (iii) The stars with [Fe/H]<-0.1 are old with ages between 10 and 12 Gyr; (iv) The metal-rich stars with [Fe/H]>-0.1 show a wide variety of ages, ranging from 2 to 12 Gyr with a distribution that has a dominant peak around 4-5 Gyr and a tail towards higher ages; (v) There are indications in the [alpha/Fe] - [Fe/H] that the "knee" occurs around [Fe/H] = -0.3 to -0.2, which is a slightly higher metallicity as compared to the "knee" for the local thick disk. This suggests that the chemical enrichment of the metal-poor bulge has been somewhat faster than what is observed for the local thick disk. The results from the microlensed bulge dwarf stars in combination with other findings in the literature, in particular the evidence that the bulge has cylindrical rotation, indicate that the Milky Way could be an almost pure disk galaxy. The bulge would then just be a conglomerate of the other Galactic stellar populations (thin disk, thick disk, halo, and ...?), residing together in the central parts of the Galaxy, influenced by the Galactic bar.
We present the results of Giant Metrewave Radio Telescope (GMRT) observations to detect H{\sc i} in absorption towards the cores of a sample of radio galaxies. From observations of a sample of 16 sources, we detect H{\sc i} in absorption towards the core of only one source, the FR\,II radio galaxy 3C\,452 which has been reported earlier by Gupta & Saikia (2006a). In this paper we present the results for the remaining sources which have been observed to a similar optical depth as for a comparison sample of compact steep-spectrum (CSS) and giga-hertz peaked spectrum (GPS) sources. We also compile available information on H{\sc i} absorption towards the cores of extended radio sources observed with angular resolutions of a few arcsec or better. The fraction of extended sources with detection of H{\sc i} absorption towards their cores is significantly smaller (7/47) than the fraction of H{\sc i} detection towards CSS and GPS objects (28/49). For the cores of extended sources, there is no evidence of a significant correlation between H{\sc i} column density towards the cores and the largest linear size of the sources. The distribution of the relative velocity of the principal absorbing component towards the cores of extended sources is not significantly different from that of the CSS and GPS objects. However, a few of the CSS and GPS objects have blue-shifted components $\gapp$1000 km s$^{-1}$, possibly due to jet-cloud interactions. With the small number of detections towards cores, the difference in detection rate between FR\,I (4/32) and FR\,II (3/15) sources is within the statistical uncertainties.
We study the thermal evolution of primordial star-forming gas clouds using three-dimensional cosmological simulations. We critically examine how assumptions and approximations made in calculating radiative cooling rates affect the dynamics of the collapsing gas clouds. We consider two important molecular hydrogen cooling processes that operate in a dense primordial gas; H_2 line cooling and continuum cooling by H_2 collision-induced emission. To calculate the optically thick cooling rates, we follow the Sobolev method for the former, whereas we perform ray-tracing for the latter. We also run the same set of simulations using simplified fitting functions for the net cooling rates. We compare the simulation results in detail. We show that the time- and direction-dependence of hydrodynamic quantities such as gas temperature and local velocity gradients significantly affects the optically thick cooling rates. Gravitational collapse of the cloud core is accelerated when the cooling rates are calculated by using the fitting functions. The structure and evolution of the central pre-stellar disk are also affected. We conclude that physically motivated implementations of radiative transfer are necessary to follow accurately the thermal and chemical evolution of a primordial gas to high densities.
We carry out plasma diagnostic analyses for 123 planetary nebulae (PNe) and 42 H II regions using the N II and O II optical recombination lines (ORLs). New effective recombination coefficients for the N II and O II optical recombination spectra are used. These data were calculated under the intermediate coupling scheme for a number of electron temperature (Te) and density (Ne) cases. We used a new method to determine the Te and Ne for the nebular sample, combining the ORLs with the most reliable measurements for each ion and the predicted intensities that are based on the new atomic data. Uncertainties of the derived Te and Ne are estimated for each object. The diagnostic results from heavy element ORLs show reasonable agreement with previous calculations in the literature. We compare the electron temperatures derived from the N II and O II ORLs, Te(ORLs), and those from the collisionally excited lines (CELs), Te(CELs), as well as the hydrogen Balmer jump, Te(H I BJ), especially for the PNe with large abundance discrepancies. Temperatures from He I recombination lines, Te(He I), are also used for comparison if available. For all the objects included in our sample, Te(ORLs) are lower than Te(H I BJ), which are in turn systematically lower than Te(CELs). Nebulae with Te(He I) available show the relation Te(ORLs) < Te(He I) < Te(H I BJ) < Te(CELs), which is consistent with predictions from the bi-abundance nebular model postulated by Liu et al. (2000).
The presence of double-peaked/multicomponent emission line profiles in spectra of galaxies is commonly done by visual inspection. However, the identification of complex emission line profiles by eye is unapproachable for large databases such as the Sloan Digital Sky Survey (SDSS) or the integral field spectroscopy surveys of galaxies (e.g. CALIFA or MaNGA). We describe a quick method involving the cross-correlation technique for detecting the presence of complex (double-peaked or multiple components) profiles in the spectra of galaxies, deriving simultaneously a first estimation of the velocity dispersions and radial velocities of the dominant gaseous component. We illustrate the proposed procedure with the well-known complex [OIII]4959,5007 profiles of the central region of NGC1068.
The emergence of the magnetic field through the photosphere has multiple manifestations and sunspots are the most prominent examples of this. One of the most relevant sunspot properties, to study both its structure and evolution, is the sunspot area: either total, umbra or penumbra area. Recently Schlichenmaier et al. (2010) studied the evolution of the active region (AR) NOAA 11024 concluding that during the penumbra formation the umbra area remains constant and that the increase of the total sunspot area is caused exclusively by the penumbra growth. In this presentation the Schlichenmaier's conclusion is firstly tested, investigating the evolution of four different ARs. Hundreds of Intensitygram images from the Helioseismic and Magnetic Imager (HMI) images are used, obtained by the Solar Dynamics Observatory, in order to describe the area evolution of the above ARs and estimate the increase and decrease rates for umbra and penumbra areas, separately. A simple magnetohydrodynamic model is then tentatively used in a first approximation to explain the observed results.
Supergranulation is one of the most visible length scales of solar convection
and has been studied extensively by local helioseismology. We use synthetic
data computed with the Seismic Propagation through Active Regions and
Convection (SPARC) code to test regularized-least squares (RLS) inversions of
helioseismic holography measurements for a supergranulation-like flow. The code
simulates the acoustic wavefield by solving the linearized three-dimensional
Euler equations in Cartesian geometry. We model a single supergranulation cell
with a simple, axisymmetric, mass-conserving flow.
The use of simulated data provides an opportunity for direct evaluation of
the accuracy of measurement and inversion techniques. The RLS technique applied
to helioseismic-holography measurements is generally successful in reproducing
the structure of the horizontal flow field of the model supergranule cell. The
errors are significant in horizontal-flow inversions near the top and bottom of
the computational domain as well as in vertical-flow inversions throughout the
domain. We show that the errors in the vertical velocity are due largely to
cross talk from the horizontal velocity.
The discovery of a population of massive, compact and quiescent early-type galaxies has changed the view on plausible formation scenarios for the present day population of elliptical galaxies. Traditionally assumed formation histories dominated by 'single events' like early collapse or major mergers appear to be incomplete and have to be embedded in the context of hierarchical cosmological models with continuous gas accretion and the merging of small stellar systems (minor mergers). Once these processes are consistently taken into account the hierarchical models favor a two-phase assembly process and are in much better shape to capture the observed trends. We review some aspects of recent progress in the field.
In this paper we give an introduction to the Boltzmann equation for neutrino transport used in core collapse supernova models as well as a detailed mathematical description of the \emph{Isotropic Diffusion Source Approximation} (IDSA). Furthermore, we present a numerical treatment of a reduced Boltzmann model problem based on time splitting and finite volumes and revise the discretization of the IDSA for this problem. Discretization error studies carried out on the reduced Boltzmann model problem and on the IDSA show that the errors are of order one in both cases. By a numerical example, a detailed comparison of the reduced model and the IDSA is carried out and interpreted. For this example the IDSA modeling error with respect to the reduced Boltzmann model is numerically determined and localized.
We compute cosmic ray (CR) nuclei, proton, antiproton, electron and positron spectra below 1 TeV at Earth by means of a detailed transport description in the galaxy and in the solar system. CR spectra below 10 GeV are strongly modified by charge-sign dependent propagation effects. These depend on the polarity of the solar magnetic field and therefore vary with the solar cycle. The puzzling discrepancy between the low-energy positron fraction measured by PAMELA and AMS-01 is then easily explained by their different data-taking epochs. We reproduce the observed spectra of CR light nuclei within the same galactic and solar-system propagation model.
In this work, we investigate in detail the capabilities of present (H.E.S.S., MAGIC, VERITAS) and planned (CTA) ground-based Cherenkov telescope systems to detect angular anisotropies in the diffuse gamma-ray background. We first study the impact of instrumental characteristics (effective area, field of view, angular resolution, and background rejection efficiency) to the ability to detect anisotropies. In addition, we compare different observation strategies, i.e., whether a single deep observation or a splitting over multiple shallow fields is preferred. Secondly, the sensitivity to anisotropies generated by self-annihilating dark matter is investigated for different common dark matter models. With planned configurations of CTA, we find that a relative contribution of ~10% from dark matter annihilation to the diffuse gamma-ray background can be detected, together with the sensitivity to the self-annihilation cross section <sigma v> = 3 10^(-26) cm3s-1 expected from thermal dark matter freeze-out. We also stress the importance of constraining anisotropies from unresolved astrophysical sources already with the current generation of instruments, as a novel and complementary method to constrain the properties of TeV sources.
We present results from GMRT HI 21 cm line observations of the interacting galaxy pair Arp 181 (NGC 3212 and NGC 3215) at z =0.032. We find almost all of the detected HI (90%) displaced well beyond the optical disks of the pair with the highest density HI located ~70 kpc west of the pair. An HI bridge extending between the optical pair and the bulk of the HI together with their HI deficiencies provide strong evidence that the interaction between the pair has removed most of their HI to the current projected position. HI to the west of the pair has two approximately equal intensity peaks. The HI intensity maximum furthest to the west coincides with a small spiral companion SDSS J102726.32+794911.9 which shows enhanced mid-infrared (Spitzer), UV (GALEX) and H alpha emission indicating intense star forming activity. The HI intensity maximum close to the Arp 181 pair, coincides with a diffuse optical cloud detected in UV (GALEX) at the end of the stellar and HI tidal tails originating at NGC 3212 and, previously proposed to be a tidal dwarf galaxy in formation. Future sensitive HI surveys by telescopes like ASKAP should prove to be powerful tools for identifying tidal dwarfs at moderate to large redshifts to explore in detail the evolution of dwarf galaxies in the Universe.
The CrA region and the Coronet cluster form a nearby (138 pc), young (1-2 Myr) star-forming region hosting a moderate population of YSO. We present Herschel PACS photometry at 100 and 160 micron, obtained as part of the Herschel Gould Belt Survey. The Herschel maps reveal the cluster members with high sensitivity and high dynamic range. Many of the cluster members are detected, including some embedded, very low-mass objects, several protostars, and substantial emission from the surrounding cloud. The Herschel data provide sufficient spatial resolution to detect small-scale details, such as bright filaments around the IRS5 protostar complex and a bubble-shaped rim associated with the Class I object IRS2. The disks around the Class II objects display a wide range of mid- and far-IR excesses consistent with different disk structures. We have modeled the disks using the RADMC radiative transfer code, finding an interesting mixture of objects for a young and presumably coeval cluster. Some of them are consistent with flared, massive, relatively primordial disks (SCrA, TCrA). Others display significant evidence for inside-out evolution, consistent with the presence of inner holes/gaps (G-85, G-87). Finally, we find disks with a dramatic small dust depletion (G-1, HBC677) that, in some cases, could be related to truncation or to the presence of large gaps in a flared disk (CrA-159). The derived masses for the disks around the low-mass stars are found to be below the typical values in Taurus, in agreement with previous Spitzer observations. Given the high degree of multiplicity and interactions observed among the protostars in the region, the diversity of disks may be a consequence of the early star formation history, which should also be taken into account when studying the disk properties in similar sparsely populated clusters.
We introduce a novel formalism to investigate the role of the spin angular momentum of astrophysical black holes in influencing the behaviour of low angular momentum general relativistic accretion. We propose a metric independent analysis of axisymmetric general relativistic flow, and consequently formulate the space and time dependent equations describing the general relativistic hydrodynamic accretion flow in the Kerr metric. The associated stationary critical solutions for such flow equations are provided, as well as the stability of the stationary transonic configuration is examined using a novel linear perturbation technique. We examine the properties of infalling material for both the prograde as well as the retrograde accretion as a function of the Kerr parameter at the extreme close proximity of the event horizon. Our formalism can be used to identify a new spectral signature of black hole spin, and has the potential of performing the black hole shadow imaging corresponding to the low angular momentum accretion flow.
We present global structural parameter measurements of 109,533 unique, H_F160W-selected objects from the CANDELS multi-cycle treasury program. Sersic model fits for these objects are produced with GALFIT in all available near-infrared filters (H_F160W, J_F125W and, for a subset, Y_F105W). The parameters of the best-fitting Sersic models (total magnitude, half-light radius, Sersic index, axis ratio, and position angle) are made public, along with newly constructed point spread functions for each field and filter. Random uncertainties in the measured parameters are estimated for each individual object based on a comparison between multiple, independent measurements of the same set of objects. To quantify systematic uncertainties we create a mosaic with simulated galaxy images with a realistic distribution of input parameters and then process and analyze the mosaic in an identical manner as the real data. We find that accurate and precise measurements -- to 10% or better -- of all structural parameters can typically be obtained for galaxies with H_F160W < 23, with comparable fidelity for basic size and shape measurements for galaxies to H_F160W ~ 24.5.
A large polar-crown prominence composed of different segments spanning nearly the entire solar disk erupted on 2010 December 6. Prior to the eruption, the filament in the active region part splits into two layers: a lower layer and an elevated layer. The eruption occurs in several episodes. Around 14:12 UT, the lower layer of the active region filament breaks apart, one part ejects towards the west, while the other part ejects towards the east, which leads to the explosive eruption of the eastern quiescent filament. During the early rise phase, part of the quiescent filament sheet displays strong rolling motion (observed by STEREO$\_$B) in the clockwise direction (views from east to west) around the filament axis. This rolling motion appears to start from the border of the active region, then propagates towards the east. AIA observes another type of rotating motion: in some other parts of the erupting quiescent prominence the vertical threads turn horizontal, then turn upside down. The elevated active region filament does not erupt until 18:00 UT, when the erupting quiescent filament already reaches a very large height. We develop two simplified three-dimensional models which qualitatively reproduce the observed rolling and rotating motions. The prominence in the models is assumed to consist of a collection of discrete blobs that are tied to particular field lines of a helical flux rope. The observed rolling motion is reproduced by continuous twist injection into the flux rope in Model 1 from the active region side. Asymmetric reconnection induced by the asymmetric distribution of the magnetic fields on the two sides of the filament may cause the observed rolling motion. The rotating motion of the prominence threads observed by AIA is consistent with the removal of the field line dips in Model 2 from the top down during the eruption.
We present further analysis of the [CII] 158$\mu$m fine structure line and thermal dust continuum emission from the archetype extreme starburst/AGN group of galaxies in the early Universe, BRI 1202-0725 at $z=4.7$, using the Atacama Large Millimeter Array. The group is long noted for having a closely separated (26kpc in projection) FIR-hyperluminous quasar host galaxy and an optically obscured submm galaxy (SMG). A short ALMA test observation reveals a rich laboratory for the study of the myriad processes involved in clustered massive galaxy formation in the early Universe. Strong [CII] emission from the SMG and the quasar have been reported earlier by Wagg et al. (2012) based on these observations. In this letter, we examine in more detail the imaging results from the ALMA observations, including velocity channel images, position-velocity plots, and line moment images. We present detections of [CII] emission from two Ly$\alpha$-selected galaxies in the group, demonstrating the relative ease with which ALMA can detect the [CII] emission from lower star formation rate galaxies at high redshift. Imaging of the [CII] emission shows a clear velocity gradient across the SMG, possibly indicating rotation or a more complex dynamical system on a scale $\sim 10$kpc. There is evidence in the quasar spectrum and images for a possible outflow toward the southwest, as well as more extended emission (a 'bridge'), between the quasar and the SMG, although the latter could simply be emission from Ly$\alpha$-1 blending with that of the quasar at the limited spatial resolution of the current observations. These results provide an unprecedented view of a major merger of gas rich galaxies driving extreme starbursts and AGN accretion during the formation of massive galaxies and supermassive black holes within 1.3 Gyr of the Big Bang.
Theory predicts that a plane wave scattered by a thin slab of gas yields, in the forward direction and under specific circumstances, a larger irradiance than would be observed in the absence of the gas. This enhanced Rayleigh scattering depends on the size of the Fresnel zones at the slab location, as seen from the observer's position, and results from the coherence of the scattering. On astronomical scales the exceptional size of Fresnel zones (~1500km) has particular relevance when considering forward-scattered starlight by an interstellar cloud of atomic hydrogen.
Non-adiabatic pressure perturbations naturally occur in models of inflation consisting of more than one scalar field. The amount of non-adiabatic pressure present at the end of inflation can have observational consequences through changes in the curvature perturbation, the generation of vorticity and subsequently the sourcing of B-mode polarisation. In this work, based on a presentation at the 13th Marcel Grossmann Meeting, we give a very brief overview of non-adiabatic pressure perturbations in multi-field inflationary models and describe our recent calculation of the spectrum of isocurvature perturbations generated at the end of inflation for different models which have two scalar fields.
We present astrometric measurements of eleven nearby ultracool brown dwarfs of spectral types Y and late-T, based on imaging observations from a variety of space-based and ground-based telescopes. These measurements have been used to estimate relative parallaxes and proper motions via maximum likelihood fitting of geometric model curves. To compensate for the modest statistical significance (<~ 7) of our parallax measurements we have employed a novel Bayesian procedure for distance estimation which makes use of an a priori distribution of tangential velocities, Vtan, assumed similar to that implied by previous observations of T dwarfs. Our estimated distances are therefore somewhat dependent on that assumption. Nevertheless, the results have yielded distances for five of our eight Y dwarfs and all three T dwarfs. Estimated distances in all cases are >~ 3 pc. In addition, we have obtained significant estimates of Vtan for two of the Y dwarfs; both are <100 km/s, consistent with membership in the thin disk population. Comparison of absolute magnitudes with model predictions as a function of color shows that the Y dwarfs are significantly redder in J-H than predicted by a cloud-free model
We present observational evidence of apparent plasma rotational motions in the feet of a solar prominence. Our study is based on spectroscopic observations taken in the He I 1083.0 nm multiplet with the Tenerife Infrared Polarimeter attached to the German Vacuum Tower Telescope. We recorded a time sequence of spectra with 34 s cadence placing the slit of the spectrograph almost parallel to the solar limb and crossing two feet of an intermediate size, quiescent hedgerow prominence. The data show opposite Doppler shifts, +/- 6 km/s, at the edges of the prominence feet. We argue that these shifts may be interpreted as prominence plasma rotating counterclockwise around the vertical axis to the solar surface as viewed from above. The evolution of the prominence seen in EUV images taken with the Solar Dynamic Observatory provided us clues to interpret the results as swirling motions. Moreover, time-distance images taken far from the central wavelength show plasma structures moving parallel to the solar limb with velocities of about 10-15 km/s. Finally, the shapes of the observed intensity profiles suggest the presence of, at least, two components at some locations at the edges of the prominence feet. One of them is typically Doppler shifted (up to 20 km/s) with respect to the other, thus suggesting the existence of supersonic counter-streaming flows along the line-of-sight.
We consider the slowly rotating relativistic stars with a uniform angular velocity in the scalar-tensor gravity, and examine the rotational effect around such compact objects. For this purpose, we derive a 2nd order differential equation describing the frame dragging in the scalar-tensor gravity and solve it numerically. As a result, we find that the total angular momentum is proportional to the angular velocity even in the scalar-tensor gravity. We also show that one can observe the spontaneous scalarization in rotational effects as well as the other stellar properties, if the cosmological value of scalar field is zero. On the other hand, if the cosmological value of scalar field is nonzero, the deviation from the general relativity can be seen in a wide range of the coupling constant. Additionally, we find that the deviation from the general relativity becomes larger with more massive stellar models, which is independent of the cosmological value of scalar field. Thus, via precise observations of astronomical phenomena associated with rotating relativistic stars, one may be possible to probe not only the gravitational theory in the strong-field regime, but also the existence of scalar field.
We present a measurement of the trigonometric parallax of IRAS 05168+3634 with VERA. The parallax is 0.532 +/- 0.053 mas, corresponding to a distance of 1.88 +0.21/-0.17 kpc. This is significantly closer than the previous distance estimate of 6 kpc based on a kinematic distance measurement. This drastic change in the source distance implies the need for revised values of not only the physical parameters of IRAS 05168+3634, but it also implies a different location in the Galaxy, placing it in the Perseus arm rather than the Outer arm. We also measured the proper motion of the source. A combination of the distance and proper motion with the systemic velocity yields a rotation velocity {\Theta} = 227 +9/-11 km s^-1 at the source position, assuming {\Theta}_0 = 240 km s^-1. Our result, combined with previous VLBI results for six sources in the Perseus arm, indicates that the sources rotate systematically more slowly than the Galactic rotation velocity at the local standard of rest. In fact, we derive peculiar motions in the disk averaged over the seven sources in the Perseus arm of (U_mean, V_mean) = (11 +/- 3, -17 +/- 3) km s^-1, which indicates that these seven sources are moving systematically toward the Galactic Center and lag behind the overall Galactic rotation.
We study how uncertainty in the reionization history of the universe affects estimates of other cosmological parameters from the Cosmic Microwave Background. We analyze WMAP7 data and synthetic Planck-quality data generated using a realistic scenario for the reionization history of the universe obtained from high-resolution numerical simulation. We perform parameter estimation using a simple sudden reionization approximation, and using the Principal Component Analysis (PCA) technique proposed by Mortonson and Hu. We reach two main conclusions: (1) Adopting a simple sudden reionization model does not introduce measurable bias into values for other parameters, indicating that detailed modeling of reionization is not necessary for the purpose of parameter estimation from future CMB data sets such as Planck. (2) PCA analysis does not allow accurate reconstruction of the actual reionization history of the universe in a realistic case.
This is an addendum to the paper by Cappellari (2008, MNRAS, 390, 71), which presented a simple and efficient method to model the stellar kinematics of axisymmetric stellar systems. The technique reproduces well the integral-field kinematics of real galaxies. It allows for orbital anisotropy (three-integral distribution function), multiple kinematic components, supermassive black holes and dark matter. The paper described the derivation of the projected second moments and we provided a reference software implementation. However only the line-of-sight component was given in the paper. For completeness we provide here all the six projected second moments, including radial velocities and proper motions. We present a test against realistic N-body galaxy simulations.
In this contribution we briefly introduce a mechanism for short gamma ray burst emission different from the usually assumed compact object binary merger progenitor model. It is based on the energy release in the central regions of neutron stars. This energy injection may be due to internal self-annihilation of dark matter gravitationally accreted from the galactic halo. We explain how this effect may trigger its full or partial conversion into a quark star and, in such a case, induce a gamma ray burst with isotropic equivalent energies in agreement with those measured experimentally. Additionally, we show how the ejection of the outer crust in such events may be accelerated enough to produce Lorentz factors over those required for gamma ray emission.
Earth-based radar observations of the rotational dynamics of Mercury (Margot
et al. 2012) combined with the determination of its gravity field by MESSENGER
(Smith et al. 2012) give clues on the internal structure of Mercury, in
particular its polar moment of inertia C, deduced from the obliquity (2.04 +/-
0.08) arcmin.
The dynamics of the obliquity of Mercury is a very-long term motion (a few
hundreds of kyrs), based on the regressional motion of Mercury's orbital
ascending node. This paper, following the study of Noyelles & D'Hoedt (2012),
aims at first giving initial conditions at any time and for any values of the
internal structure parameters for numerical simulations, and at using them to
estimate the influence of usually neglected parameters on the obliquity, like
J3, the Love number k2 and the secular variations of the orbital elements. We
use for that averaged representations of the orbital and rotational motions of
Mercury, suitable for long-term studies.
We find that J3 should alter the obliquity by 250 milli-arcsec, the tides by
100 milli-arcsec, and the secular variations of the orbital elements by 10
milli-arcsec over 20 years. The resulting value of C could be at the most
changed from 0.346mR^2 to 0.345mR^2.
The classification of clusters according to their X-ray appearance is a powerful tool to discriminate between regular clusters (associated to relaxed objects) and disturbed ones (linked to dynamically active systems). The compilation of the two subsamples is a necessary step both for cosmological studies - oriented towards spherical and virialized systems- and for astrophysical investigations - focused on phenomena typically present in highly disturbed clusters such as turbulence, particle re-acceleration, magneto-astrophysics . In this paper, we review several morphological parameters: asymmetry and fluctuation of the X-ray surface brightness, hardness ratios, X-ray surface-brightness concentration, centroid shift, and third-order power ratio. We test them against 60 Chandra-like images obtained from hydrodynamical simulations through the X-ray Map Simulator and visually classified as regular and disturbed. The best performances are registered when the parameters are computed using the largest possible region (either within R500 or 1000 kpc). The best indicators are the third-order power ratio, the asymmetry parameter, and the X-ray-surface-brightness concentration. All their combinations offer an efficient way to distinguish between the two morphological classes achieving values of purity extremely close to 1. A new parameter, M, is defined. It combines the strengths of the aforementioned indicators and, therefore, resulted to be the most effective parameter analyzed.
We take an Effective Field Theory (EFT) approach to unifying existing proposals for the origin of cosmic acceleration and its connection to cosmological observations. Building on earlier work where EFT methods were used with observations to constrain the background evolution, we extend this program to the level of the EFT of the cosmological perturbations - following the example from the EFT of Inflation. Within this framework, we construct the general theory around an assumed background which will typically be chosen to mimic Lambda-CDM, and identify the parameters of interest for constraining dark energy and modified gravity models with observations. We discuss the similarities to the EFT of Inflation, but we also identify a number of subtleties including the relationship between the scalar perturbations and the Goldstone boson of the spontaneously broken time translations. We present formulae that relate the parameters of the fundamental Lagrangian to the speed of sound, anisotropic shear stress, effective Newtonian constant, and Caldwell's varpi parameter emphasizing the connection to observations. It is anticipated that this framework will be of use in constraining individual models, as well as for placing model-independent constraints on dark energy and modified gravity model building.
The observed baryon and dark matter densities are equal up to a factor of 5. This observation indicates that the baryon asymmetry and dark matter have the same origin. The Affleck-Dine baryogenesis is one of the most promising mechanisms in this context. Q balls, which are often formed in the early Universe associated with the Affleck-Dine baryogenesis, decay both into supersymmetric particles and into quarks. Recently, it was pointed out that annihilation of squarks into quarks gives a dominant contribution to the Q-ball decay rate and the branching ratio of Q-ball decay into supersymmetric particles changes from the previous estimate. In this paper, the scenario of baryon and dark matter cogenesis from Q ball in gravity mediation is revisited in respect of the improved Q-ball decay rates. It is found that the successful cogenesis takes place when a wino with mass 400-600 GeV is dark matter.
It is shown that topological changes in space-time are necessary to make General Relativity compatible with the Newtonian limit and to solve the hierarchy of the fundamental interactions. We detail how topology and topological changes appear in General Relativity and how it leaves an observable footprint in space-time. In cosmology we show that such topological observable is the cosmic radiation produced by the acceleration of the universe. The cosmological constant is a very particular case which occurs when the expansion of the universe into the vacuum occurs only in the direction of the cosmic time flow.
In astrophysical environments, allowed Gamow-Teller (GT) transitions are important, particularly for $\beta$-decay rates in presupernova evolution of massive stars, since they contribute to the fine-tuning of the lepton-to-baryon content of the stellar matter prior to and during the collapse of a heavy star. In environments where GT transitions are unfavored, first-forbidden transitions become important especially in medium heavy and heavy nuclei. Particularly in case of neutron-rich nuclei, first-forbidden transitions are favored primarily due to the phase-space amplification for these transitions. In this work the total $\beta$-decay half-lives and the unique first-forbidden(U1F) $\beta$-decay rates for a number of neutron-rich nickel isotopes, $^{72-78}$Ni, are calculated using the proton-neutron quasi-particle random phase approximation (pn-QRPA) theory for the first time in stellar matter. For the calculation of the $\beta$-decay half-lives both allowed and first-forbidden transitions were considered. Comparison of the total half-lives is made with measurements and other theoretical calculation. The pn-QRPA results agree reasonably well with experiments.
The observation of earth skimming neutrinos has been proposed as a rather sensitive method to detect ultra-high energy (UHE) cosmic neutrinos. Energetic cosmic neutrinos can interact inside the rock and produce leptons via a charged current interaction. In the case of an incoming electron neutrino undergoing a charged current interaction, the produced UHE electron will induce an underground electromagnetic shower. At high energy (above 7.7 TeV in standard rock), such showers are subject to LPM (Landau, Pomeranchuk and Migdal) suppression of the radiative processes cross sections (bremsstrahlung and pair production). The consequence of this suppression is that showers are elongated. This effect will increase the detection probability of such events allowing deeper showers to emerge with detectable energies. On the other hand, the photonuclear processes which are usually neglected in electromagnetic showers with respect to radiative processes, turn out to become dominant in the LPM regime and will reduce the shower length. In this work, we have performed a complete Monte Carlo study of an underground shower induced by UHE electrons by taking into account both the LPM suppression and the photonuclear interaction. We will discuss the effects of both of these processes on the shower length and on the detectability of such events by ground arrays or fluorescence telescopes. We show that limits on neutrino fluxes that were obtained using simulations that were obviously neglecting photonuclear processes are overoptimistic and should be corrected.
Depending on the type and arrangement of metastable vacua in the theory, initial conditions in a de Sitter vacuum with arbitrarily large entropy can be compatible with the observed arrow of time, if the causal patch or related measures are used to regulate divergences. An important condition, however, is that the initial vacuum cannot produce observers from rare fluctuations (Boltzmann brains). Here we consider more general initial conditions where multiple vacua have nonzero initial probability. We examine whether the prediction of an arrow of time is destroyed by a small initial admixture of vacua that can produce Boltzmann brains. We identify general criteria and apply them to two nontrivial examples of such initial probability distributions. The Hartle-Hawking state is superexponentially dominated by the vacuum with smallest positive cosmological constant, so one might expect that other initial vacua can be neglected; but in fact, their inclusion drastically narrows the range of theory parameters for which an arrow of time is predicted. The dominant eigenvector of the global rate equation of eternal inflation is dominated by the longest-lived metastable vacuum. If an arrow of time emerges in the single-initial-vacuum approximation, then we find that this conclusion survives the admixture of other initial vacua. By global-local measure duality, this result amounts to a successful consistency test of certain global cutoffs, including light-cone time and scale-factor time.
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