We present here the observation of the Cygnus Superbubble (CSB) using the Solid-state slit camera (SSC) aboard the Monitor of All-sky X-ray Image. The CSB is a large diffuse structure in the Cygnus region with enhanced soft X-ray emission. By utilizing the CCD spectral resolution of the SSC, we detect Fe, Ne, Mg emission lines from the CSB for the first time. The best fit model implies thin hot plasma of kT ~ 0.3 keV with depleted abundance of 0.26 +/- 0.1 solar. Joint spectrum fitting of the ROSAT PSPC data and MAXI/SSC data enables us to measure precise values of NH and temperature inside the CSB. The results show that all of the regions in the CSB have similar NH and temperature, indicating that the CSB is single unity. The energy budgets calculation suggests that 2-3 Myrs of stellar wind from the Cyg OB2 is enough to power up the CSB, whereas due to its off center position, the origin of the CSB is most likely a Hypernova.
We measure the sum of the neutrino particle masses using the three-dimensional galaxy power spectrum of the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9 (DR9) CMASS galaxy sample. Combined with the cosmic microwave background (CMB), supernova (SN) and additional baryonic acoustic oscillation (BAO) data, we find upper 95 percent confidence limits of the neutrino mass \Sigma m_{\nu}<0.340 eV within a flat \Lambda CDM background, and \Sigma m_{\nu}<0.821 eV, assuming a more general background cosmological model. The number of neutrino species is measured to be N_{eff}=4.308\pm0.794 and N_{eff}=4.032^{+0.870}_{-0.894} for these two cases respectively. We study and quantify the effect of several factors on the neutrino measurements, including the galaxy power spectrum bias model, the effect of redshift-space distortion, the cutoff scale of the power spectrum, and the choice of additional data. The impact of neutrinos with unknown masses on other cosmological parameter measurements is investigated. The fractional matter density and the Hubble parameter are measured to be \Omega_M=0.2796\pm0.0097, H_0=69.72^{+0.90}_{-0.91} km/s/Mpc (flat \Lambda CDM) and \Omega_M=0.2798^{+0.0132}_{-0.0136}, H_0=73.78^{+3.16}_{-3.17} km/s/Mpc (more general background model). Based on a Chevallier-Polarski-Linder (CPL) parametrisation of the equation-of-state w of dark energy, we find that w=-1 is consistent with observations, even allowing for neutrinos. Similarly, the curvature \Omega_K and the running of the spectral index \alpha_s are both consistent with zero. The tensor-to-scaler ratio is constrained down to r<0.198 (95 percent CL, flat \Lambda CDM) and r<0.440 (95 percent CL, more general background model).
Rotation is thought to be a major factor in the evolution of massive stars,
especially at low metallicity, with consequences for their chemical yields,
ionizing flux and final fate. The natal rotation-rate distribution of stars is
of high priority given its importance as a constraint on theories of massive
star formation and as input for models of stellar populations in the local
Universe and at high redshift. Recently, it has become clear that the majority
of massive stars interact with a binary companion before they die. We
investigate how this affects the distribution of rotation rates.
For this purpose, we simulate a massive binary-star population typical for
our Galaxy assuming continuous star formation. We find that, because of binary
interaction, 20^+5_-10% of all massive main-sequence stars have projected
rotational velocities in excess of 200km/s. We evaluate the effect of uncertain
input distributions and physical processes and conclude that the main
uncertainties are the mass transfer efficiency and the possible effect of
magnetic braking, especially if magnetic fields are generated or amplified
during mass accretion and stellar mergers.
The fraction of rapid rotators we derive is similar to that observed. If
indeed mass transfer and mergers are the main cause for rapid rotation in
massive stars, little room remains for rapidly rotating stars that are born
single. This implies that spin down during star formation is even more
efficient than previously thought. In addition, this raises questions about the
interpretation of the surface abundances of rapidly rotating stars as evidence
for rotational mixing. Furthermore, our results allow for the possibility that
all early-type Be stars result from binary interactions and suggest that
evidence for rotation in explosions, such as long gamma-ray bursts, points to a
binary origin.
[Abridged] The spatially averaged global spectrum of the redshifted 21cm line has generated much experimental interest, for it is potentially a direct probe of the Epoch of Reionization and the Dark Ages. Since the cosmological signal here has a purely spectral signature, most proposed experiments have little angular sensitivity. This is worrisome because with only spectra, the global 21cm signal can be difficult to distinguish from foregrounds such as Galactic synchrotron radiation, as both are spectrally smooth and the latter is orders of magnitude brighter. We establish a mathematical framework for global signal data analysis in a way that removes foregrounds optimally, complementing spectra with angular information. We explore various experimental design trade-offs, and find that 1) with spectral-only methods, it is impossible to mitigate errors that arise from uncertainties in foreground modeling; 2) foreground contamination can be significantly reduced for experiments with fine angular resolution; 3) most of the statistical significance in a positive detection during the Dark Ages comes from a characteristic high-redshift trough in the 21cm brightness temperature; and 4) Measurement errors decrease more rapidly with integration time for instruments with fine angular resolution. We show that if observations and algorithms are optimized based on these findings, an instrument with a 5 degree beam can achieve highly significant detections (greater than 5-sigma) of even extended (high Delta-z) reionization scenarios after integrating for 500 hrs. This is in contrast to instruments without angular resolution, which cannot detect gradual reionization. Abrupt ionization histories can be detected at the level of 10-100's of sigma. The expected errors are also low during the Dark Ages, with a 25-sigma detection of the expected cosmological signal after only 100 hrs of integration.
We present the direct imaging discovery of an extrasolar planet, or possible low-mass brown dwarf, at a projected separation of 55 +/- 2 AU (1.058 +/- 0.007 arcsec) from the B9-type star Kappa And. The planet was detected with Subaru/HiCIAO during the SEEDS survey, and confirmed as a bound companion via common proper motion measurements. Observed near-infrared magnitudes of J = 16.3 +/- 0.3, H = 15.2 +/- 0.2, Ks = 14.6 +/- 0.4, and L' = 13.12 +/- 0.09 indicate a temperature of ~1700 K. The galactic kinematics of the host star are consistent with membership in the Columba association, implying a corresponding age of 30 +20 -10 Myr. The system age, combined with the companion photometry, points to a model-dependent companion mass ~12.8 MJup. The host star's estimated mass of 2.4-2.5 Msun places it among the most massive stars ever known to harbor an extrasolar planet or low-mass brown dwarf. While the mass of the companion is close to the deuterium burning limit, its mass ratio, orbital separation, and likely planet-like formation scenario imply that it may be best defined as a `Super-Jupiter' with properties similar to other recently discovered companions to massive stars.
The Herschel survey of the Galactic Plane (Hi-GAL) provides a unique opportunity to study star formation over large areas of the sky and different environments in the Milky Way. We use the best studied Hi-GAL fields to date, two 2x2 tiles centered on (l, b) = (30, 0) deg and (l, b) = (59, 0) deg, to study the star formation activity using a large sample of well selected young stellar objects (YSOs). We estimate the star formation rate (SFR) for these fields using the number of candidate YSOs and their average time scale to reach the Zero Age Main Sequence, and compare it with the rate estimated using their integrated luminosity at 70 micron combined with an extragalactic star formation indicator. We measure a SFR of (9.5 +- 4.3)*10^{-4} Msol/yr and (1.6 +- 0.7)*10^{-4} Msol/yr with the source counting method, in l=30 deg and l=59 deg, respectively. Results with the 70 micron estimator are (2.4 +- 0.4)*10^{-4} Msol/yr and (2.6 +- 1.1)*10^{-6} Msol/yr. Since the 70 micron indicator is derived from averaging extragalactic star forming complexes, we perform an extrapolation of these values to the whole Milky Way and obtain SFR_{MW} = (0.71 +- 0.13) Msol/yr from l = 30 deg and SFR_{MW} = (0.10 +- 0.04) Msol/yr from l=59 deg. The estimates in l=30 deg are in agreement with the most recent results on the Galactic star formation activity, indicating that the characteristics of this field are likely close to those of the star-formation dominated galaxies used for its derivation. Since the sky coverage is limited, this analysis will improve when the full Hi-GAL survey will be available.
We study the statistics and cosmic evolution of massive black hole seeds formed during major mergers of gas-rich late-type galaxies. Generalizing the results of the hydro-simulations from Mayer et al. 2010, we envision a scenario in which a supermassive star can form at the center of galaxies that just experienced a major merger owing to a multi-scale powerful gas inflow, provided that such galaxies live in haloes with masses above 10^{11} Msun, are gas-rich and disc-dominated, and do not already host a massive black hole. We assume that the ultimate collapse of the supermassive star leads to the rapid formation of a black hole of 10^5 Msun following a quasi-star stage. Using a model for galaxy formation applied to the outputs of the Millennium Simulation, we show that the conditions required for this massive black hole formation route to take place in the concordance LambdaCDM model are actually common at high redshift, and can be realized even at low redshift. Most major mergers above z~4 in haloes with mass > 10^{11} Msun can lead to the formation of a massive seed and, at z~2, the fraction of favourable mergers decreases to about half. Interestingly, we find that even in the local universe a fraction (~20%) of major mergers in massive haloes still satisfy the conditions for our massive black hole formation route. Those late events take place in galaxies with a markedly low clustering amplitude, that have lived in isolation for most of their life, and that are experiencing a major merger for the first time. We predict that massive black hole seeds from galaxy mergers can dominate the massive end of the mass function at high (z>4) and intermediate (z~2) redshifts relative to lighter seeds formed at higher redshift, for example, by the collapse of Pop III stars. Finally, a fraction of these massive seeds could lie, soon after formation, above the MBH-MBulge relation.
The Giant GAlaxies, Dwarfs, and Debris Survey concentrates on the nearby universe to study how galaxies have interacted in groups of different morphology, density, and richness. In these groups we select the dominant spiral galaxy and search its surroundings for dwarf galaxies and tidal interactions. This paper presents the first results from deep wide-field imaging of NGC 7331, where we detect only four low luminosity candidate dwarf companions and a stellar stream that may be evidence of a past tidal interaction. The dwarf galaxy candidates have surface brightnesses of mu_{r} ~ 23-25 mag/arcsec^{2} with (g-r) colors of 0.57-0.75mag in the Sloan Digital Sky Survey filter system, consistent with their being dwarf spheroidal galaxies (dSph). A faint stellar stream structure on the western edge of NGC 7331 has mu_{g} ~27 mag/arcsec^{2} and a relatively blue color of (g-r)=0.15mag. If it is tidal debris, then this stream could have probably formed from a rare type of interaction between NGC 7331 and a dwarf irregular or transition-type dwarf galaxy. We compare the structure and local environments of NGC 7331 to those of other nearby giant spirals in small galaxy groups. NGC 7331 has a much lower (2%) stellar mass in the form of early-type satellites than found for M31 and lacks the presence of nearby companions like luminous dwarf elliptical galaxies or the Magellanic Clouds. However, our detection of a few dSph candidates suggests that it is not deficient in low-luminosity satellites.
Once understood as the paradigm of passively evolving objects, the discovery that massive galaxies experienced an enormous structural evolution in the last ten billion years has opened an active line of research. The most significant pending question in this field is the following: which mechanism has made galaxies to grow largely in size without altering their stellar populations properties dramatically? The most viable explanation is that massive galaxies have undergone a significant number of minor mergers which have deposited most of their material in the outer regions of the massive galaxies. This scenario, although appealing, is still far from be observationally proved since the number of satellite galaxies surrounding the massive objects appears insufficient at all redshifts. The presence also of a population of nearby massive compact galaxies with mixture stellar properties is another piece of the puzzle that still does not nicely fit within a comprehensive scheme. I will review these and other intriguing properties of the massive galaxies in this contribution.
We present joint constraints on the distribution of MgII absorption around galaxies, by combining the MgII absorption seen in stacked background galaxy spectra and the distribution of host galaxies of strong MgII systems from the spectra of background quasars. We present a suite of models that predict, the dependence of MgII absorption on a galaxy's apparent inclination, impact parameter(b) and azimuthal angle. The variations in the absorption strength with azimuthal angles provide much stronger constraints on the intrinsic geometry of the MgII absorption than the dependence on the galaxy's inclination. Strong MgII absorbers (W_r(2796)>0.3) are asymmetrically distributed in azimuth around their host galaxies:72% of the absorbers studied and 100% of the close-in absorbers within b<38 kpc, are located within 50deg of the host galaxy's projected minor axis. Composite models consisting either of a simple bipolar component plus a spherical or disk component, or a single highly softened bipolar distribution, can well represent the azimuthal dependencies observed in both the datasets. Simultaneously fitting both datasets to the composite model, bipolar cone is confined to 50deg of the minor axis and contains 2/3 of the total MgII absorption. The single softened cone model has an exponential fall off with azimuth with an exponential scale-length in opening angle of 45deg. We conclude that the distribution of MgII gas at low impact parameters is not the same as that found at high impact parameters. MgII absorption within 40 kpc primarily arises from cool MgII gas entrained in winds. Beyond 40 kpc, there is evidence for a more symmetric distribution, significantly different from that closer into the galaxies. Here a significant component appears aligned more with the disk and is possibly inflowing, perhaps as part of a galactic fountain or the inflow of material from further out in the system.
We report direct evidence for asymmetry in the early phases of SN 1987A via optical spectroscopy of five fields of its light echo system. The light echoes allow the first few hundred days of the explosion to be reobserved, with different position angles providing different viewing angles to the supernova. Light echo spectroscopy therefore allows a direct spectroscopic comparison of light originating from different regions of the photosphere during the early phases of SN 1987A. Gemini multi-object spectroscopy of the light echo fields shows fine-structure in the H-alpha line as a smooth function of position angle on the near-circular light echo rings. H-alpha profiles originating from the northern hemisphere of SN 1987A show an excess in redshifted emission and a blue knee, while southern hemisphere profiles show an excess of blueshifted H-alpha emission and a red knee. This fine-structure is reminiscent of the "Bochum event" originally observed for SN 1987A, but in an exaggerated form. Maximum deviation from symmetry in the H-alpha line is observed at position angles 16 and 186 degrees, consistent with the major-axis of the expanding elongated ejecta. The asymmetry signature observed in the H-alpha line smoothly diminishes as a function of viewing angle away from the poles of the elongated ejecta. We propose an asymmetric two-sided distribution of 56Ni most dominant in the southern far quadrant of SN 1987A as the most probable explanation of the observed light echo spectra. This is evidence that the asymmetry of high-velocity 56Ni in the first few hundred days after explosion is correlated to the geometry of the ejecta some 25 years later.
We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073,
announced by the Microlensing Observations in Astrophysics survey on
2010-03-18.
This event was remarkable because the source was previously known to be
photometrically variable. Analyzing the pre-event source lightcurve, we
demonstrate that it is an irregular variable over time scales >200d. Its
dereddened color, $(V-I)_{S,0}$, is 1.221$\pm$0.051mag and from our lens model
we derive a source radius of 14.7$\pm$1.3 $R_{\odot}$, suggesting that it is a
red giant star.
We initially explored a number of purely microlensing models for the event
but found a residual gradient in the data taken prior to and after the event.
This is likely to be due to the variability of the source rather than part of
the lensing event, so we incorporated a slope parameter in our model in order
to derive the true parameters of the lensing system.
We find that the lensing system has a mass ratio of q=0.0654$\pm$0.0006. The
Einstein crossing time of the event, $T_{\rm{E}}=44.3$\pm$0.1d, was
sufficiently long that the lightcurve exhibited parallax effects. In addition,
the source trajectory relative to the large caustic structure allowed the
orbital motion of the lens system to be detected. Combining the parallax with
the Einstein radius, we were able to derive the distance to the lens,
$D_L$=2.8$\pm$0.4kpc, and the masses of the lensing objects. The primary of the
lens is an M-dwarf with $M_{L,p}$=0.16$\pm0.03M_{\odot}$ while the companion
has $M_{L,s}$=11.0$\pm2.0M_{\rm{J}}$ putting it in the boundary zone between
planets and brown dwarfs.
ALMA is estimated to generate TB scale data during only one observation; astronomers manage to identify which part of the data they are really interested in. Now we have been developing new GUI software for this purpose utilizing the VO interface: ALMA Web Quick Look System (ALMAWebQL) and ALMA Desktop Application (Vissage). The former is written in JavaScript and HTML5 generated from Java codes by Google Web Toolkit, and the latter is in pure Java. An essential point of our approach is how to reduce network traffic: we prepare, in advance, "compressed" FITS files of 2x2x1 (horizontal, vertical, and spectral directions, respectively) binning, 2x2x2 binning, 4x4x2 binning data, and so on. These files are hidden from users, and Web QL automatically choose proper one by each user operation. Through this work, we find that network traffic in our system is still a bottleneck towards TB scale data distribution. Hence we have to develop alternative data containers for much faster data processing. In this paper, I introduce our data analysis systems, and describe what we learned through the development.
SARAS is a correlation spectrometer purpose designed for precision measurements of the cosmic radio background and faint features in the sky spectrum at long wavelengths that arise from redshifted 21-cm from gas in the reionization epoch. SARAS operates in the octave band 87.5-175 MHz. We present herein the system design arguing for a complex correlation spectrometer concept. The SARAS design concept provides a differential measurement between the antenna temperature and that of an internal reference termination, with measurements in switched system states allowing for cancellation of additive contaminants from a large part of the signal flow path including the digital spectrometer. A switched noise injection scheme provides absolute spectral calibration. Additionally, we argue for an electrically small frequency-independent antenna over an absorber ground. Various critical design features that aid in avoidance of systematics and in providing calibration products for the parametrization of other unavoidable systematics are described and the rationale discussed. The signal flow and processing is analyzed and the response to noise temperatures of the antenna, reference termination and amplifiers is computed. Multi-path propagation arising from internal reflections are considered in the analysis, which includes a harmonic series of internal reflections. We opine that the SARAS design concept is advantageous for precision measurement of the absolute cosmic radio background spectrum; therefore, the design features and analysis methods presented here are expected to serve as a basis for implementations tailored to measurements of a multiplicity of features in the background sky at long wavelengths, which may arise from events in the dark ages and subsequent reionization era.
AGN feedback is of primary importance in injecting energy in the central regions of galaxy clusters and influences the global properties the intra-cluster medium (ICM) . Comparing the observed entropy profiles, within $r_{500}$, from the Representative XMM-Newton Cluster Structure Survey (REXCESS) to profiles predicted by adiabatic simulations, we estimate the non-gravitational energy, $E_{ICM}$, contained in the ICM. Adding the radiative energy losses we estimate the total energy feedback, $E_{Feedback}$, from the AGN's (the central AGN in most cases). The profiles for $E_{ICM}$, $ \Delta E_{ICM}$ in the inner regions differ for Cool-Core (CC) and Non Cool-Core (NCC) clusters and assume a similar profile after accounting for the radiation loss in CC clusters. We propose that $\Delta E_{ICM}$ is a natural indicator of CC-vs-NCC clusters. The feedback energy scales with temperature as $E_{Feedback} \propto T_{sp}^{2.57}$ for the entire sample with a scatter of $\approx 14%$. The mean energy per particle within $R_{500}$ is $\epsilon_{ICM} (R_{500})= 2.54 \pm 0.78 keV $. We use the NRAO/VLA Sky Survey (NVSS) source catalog to determine the radio luminosity at 1.4 GHz of the central source(s) of our sample. $E_{Feedback}$ shows a strong correlation with $L_R$, with different normalizations for CC and NCC clusters above $T> 3$ keV, indicating that AGN feedback from the central galaxies may provide a significant component of the feedback. CC clusters show a greater $L_R$ for a given value of feedback energy than NCC clusters. Below this temperature $E_{Feedback}$ is however significantly lower for the same value of $L_R$ showing a lower efficiency of feedback. We study the properties of the brightest central galaxy (BCG) and find a mild correlation between the BCG heating rate and the feedback energy.
The Planck Early Release Compact Source Catalog (ERCSC) has offered the first opportunity to accurately determine the luminosity function of dusty galaxies in the very local Universe (i.e. distances <~ 100 Mpc), at several (sub-)millimetre wavelengths, using blindly selected samples of low redshift sources, unaffected by cosmological evolution. This project, however, requires careful consideration of a variety of issues including the choice of the appropriate flux density measurement, the separation of dusty galaxies from radio sources and from Galactic sources, the correction for the CO emission, the effect of density inhomogeneities, and more. We present estimates of the local luminosity functions at 857 GHz (350 microns), 545 GHz (550 microns) and 353 GHz (850 microns) extending across the characteristic luminosity L_star, and a preliminary estimate over a limited luminosity range at 217 GHz (1382 microns). At 850 microns and for luminosities L >~ L_star our results agree with previous estimates, derived from the SCUBA Local Universe Galaxy Survey (SLUGS), but are higher than the latter at L <~ L_star. We also find good agreement with estimates at 350 and 500 microns based on preliminary Herschel survey data.
We have carried out 12CO J=2-1 and 12CO J=3-2 observations toward the high-mass protostellar candidate IRAS 20188+3928. Compared with previous observations, the 12CO J=2-1 and 12CO J=3-2 lines both have asymmetric profiles with an absorption dip. The velocity of the absorption dip is 1.0 km/s. The spectral shape may be caused by rotation. The velocity-integrated intensity map and position-velocity diagram of the 12CO J=2-1 line present an obvious bipolar component, further verifying that this region has an outflow motion. This region is also associated with an HII region, an IRAS source, and an H2O maser. The H2O maser has the velocity of 1.1 km/s. Compared with the components of the outflow, we find that the H2O maser is not associated with the outflow. Using the large velocity gradient model, we concluded that possible averaged gas densities of the blueshifted lobe and redshifted lobe are 1.0*10^{5}$ cm^{-3} and 2.0*10$^{4} cm^{-3}, while kinetic temperatures are 26.9 K and 52.9 K, respectively. Additionally, the outflow has {a} higher integrated intensity ratio (I_{CO J=3-2}/I_{CO J=2-1}).
We present analyses to determine the fundamental parameters of the Galaxy based on VLBI astrometry of 52 Galactic maser sources obtained with VERA, VLBA and EVN. We model the Galaxy's structure with a set of parameters including the Galaxy center distance R_0, the angular rotation velocity at the LSR Omega_0, mean peculiar motion of the sources with respect to Galactic rotation (U_src, V_src, W_src), rotation-curve shape index, and the V component of the Solar peculiar motions V_sun. Based on a Markov chain Monte Carlo method, we find that the Galaxy center distance is constrained at a 5% level to be R_0 = 8.05 +/- 0.45 kpc, where the error bar includes both statistical and systematic errors. We also find that the two components of the source peculiar motion U_src and W_src are fairly small compared to the Galactic rotation velocity, being U_src = 1.0 +/- 1.5 km/s and W_src = -1.4 +/- 1.2 km/s. Also, the rotation curve shape is found to be basically flat between Galacto-centric radii of 4 and 13 kpc. On the other hand, we find a linear relation between V_src and V_sun as V_src = V_sun -19 (+/- 2) km/s, suggesting that the value of V_src is fully dependent on the adopted value of V_sun. Regarding the rotation speed in the vicinity of the Sun, we also find a strong correlation between Omega_0 and V_sun. We find that the angular velocity of the Sun, Omega_sun, which is defined as Omega_sun = Omega_0 + V_sun/R_0, can be well constrained with the best estimate of Omega_sun = 31.09 +/- 0.78 km/s. This corresponds to Theta_0 = 238 +/- 14 km/s if one adopts the above value of R_0 and recent determination of V_sun ~ 12 km/s.
Aims. The main purpose is to map the radial variation of the stellar space density for the young stellar population in the Galactic anticenter direction in order to understand the structure and location of the Perseus spiral arm. Methods. A uvbyHbeta Stromgren photometric survey covering 16sqrdeg in the anticenter direction was carried out using the Wide Field Camera at the Isaac Newton Telescope. This is the natural photometric system for identifying young stars and obtaining accurate estimates of individual distances and ages. The calibration to the standard system was undertaken using open clusters. Results. We present a main catalog of 35974 stars with all Stromgren indexes and a more extended one with 96980 stars with partial data. The central 8sqrdeg have a limiting magnitude of V<17m, while the outer region reaches V<15.5m. These large samples will permit us to analyze the stellar surface density variation associated to the Perseus arm also to study the properties of the stellar component and the interstellar extinction in the anticenter direction.
Context: Relaxation theory offers a straightforward method for estimating the energy that is released when a magnetic field becomes unstable, as a result of continual convective driving. Aims: We present new results obtained from nonlinear magnetohydrodynamic (MHD) simulations of idealised coronal loops. The purpose of this work is to determine whether or not the simulation results agree with Taylor relaxation, which will require a modified version of relaxation theory applicable to unbounded field configurations. Methods: A three-dimensional (3D) MHD Lagrangian-remap code is used to simulate the evolution of a line-tied cylindrical coronal loop model. This model comprises three concentric layers surrounded by a potential envelope; hence, being twisted locally, each loop configuration is distinguished by a piecewise-constant current profile. Initially, all configurations carry zero-net-current fields and are in ideally unstable equilibrium. The simulation results are compared with the predictions of helicity conserving relaxation theory. Results: For all simulations, the change in helicity is no more than 2% of the initial value; also, the numerical helicities match the analytically-determined values. Magnetic energy dissipation predominantly occurs via shock heating associated with magnetic reconnection in distributed current sheets. The energy release and final field profiles produced by the numerical simulations are in agreement with the predictions given by a new model of partial relaxation theory: the relaxed field is close to a linear force free state; however, the extent of the relaxation region is limited, while the loop undergoes some radial expansion. Conclusions: The results presented here support the use of partial relaxation theory, specifically, when calculating the heating-event distributions produced by ensembles of kink-unstable loops.
The Cherenkov Telescope Array (CTA) is a future instrument for very-high-energy (VHE) gamma-ray astronomy that is expected to deliver an order of magnitude improvement in sensitivity over existing instruments. In order to meet the physics goals of CTA in a cost-effective way, Monte Carlo simulations of the telescope array are used in its design. Specifically, we simulate large arrays comprising numerous large-size, medium-size and small-size telescopes whose configuration parameters are chosen based on current technical design studies and understanding of the costs involved. Subset candidate arrays with various layout configurations are then selected and evaluated in terms of key performance parameters, such as the sensitivity. This is carried out using a number of data analysis methods, some of which were developed within the field and extended to CTA, while others were developed specifically for this purpose. We outline some key results from recent studies that illustrate our approach to the optimization of the CTA design.
We follow the scenario of formation of second generation stars in globular clusters by matter processed by hot bottom burning (HBB) in massive asymptotic giant branch (AGB) stars and Super AGB stars (SAGB). In the cluster NGC 2419 we assume the presence of an extreme population directly formed from the AGB and SAGB ejecta, so we can directly compare the yields for a metallicity Z=0.0003 with the chemical inventory of the cluster NGC 2419. At such a low metallicity, the HBB temperatures (well above 108K) allow a very advanced nucleosynthesis. Masses of about 6Mo deplete Mg and synthesize Si, going beyond Al, so this latter element results only moderately enhanced; sodium can not be enhanced. The models are consistent with the observations, although the predicted Mg depletion is not as strong as in the observed stars. We predict that the oxygen abundance must be depleted by a huge factor in the Mg poor stars. The HBB temperatures are close to the region where other p capture reactions on heavier nuclei become possible. We show that high potassium abundance found in Mg poor stars can be achieved during HBB, by p captures on the argon nuclei, if the relevant cross section(s) are larger than listed in the literature or if the HBB temperature is higher. Finally, we speculate that some calcium production is occurring owing to proton capture on potassium. We emphasize the importance of a strong effort to measure a larger sample of abundances in this cluster.
We study the evolution of the Earth collision probability of asteroid 2008 TC3 using a short observational arc and small numbers of observations. To assess impact probability, we use techniques that rely on the orbital-element probability density function characterized using both Markov-chain Monte-Carlo orbital ranging and Monte-Carlo ranging. First, we evaluate the orbital uncertainties for the object from the night of discovery onwards and examine the collapse of the orbital-element distributions in time. Second, we examine the sensitivity of the results to the assumed astrometric noise. Each of the orbits obtained from the MCMC ranging method is propagated into the future (within chosen time bounds of the expected impact), and the collision probability is calculated as a weighted fraction of the orbits leading to a collision from the Earth. We compare the results obtained with both methods.
We present three newly discovered globular clusters (GCs) in the Local Group dwarf irregular NGC 6822. Two are luminous and compact, while the third is a very low luminosity diffuse cluster. We report the integrated optical photometry of the clusters, drawing on archival CFHT/Megacam data. The spatial positions of the new GCs are consistent with the linear alignment of the already-known clusters. The most luminous of the new GCs is also highly elliptical, which we speculate may be due to the low tidal field in its environment.
We devise a fast and optimal estimator for the amplitude of the bispectrum of clustered Infrared (IR) point-sources. We show how this estimator can account for the cases of partial sky coverage and inhomogeneous noise. Expected detection significance are presented in terms of signal-to-noise, finding that the IR bispectrum will realistically be undetectable below 220 GHz with a Planck-like experiment; on the contrary detection may be achieved at, or above, 220 GHz especially if the CMB is removed. We also show how this estimator can be combined with estimators of radio and CMB non-Gaussianity to build up joint robust constraints. On the one hand, we find that, for a Planck-like experiment, CMB non-Gaussianity estimation can be decoupled from point-source contributions, unless few sources are masked. On the other hand, we find that the estimation of radio and IR non-Gaussianity are strongly coupled, which diminishes their separate detection significance.
We analyze and compare the bulges of a sample of L* spiral galaxies in hydrodynamical simulations in a cosmological context, using two different codes, P-DEVA and GASOLINE. The codes regulate star formation in very different ways, with P-DEVA simulations inputing low star formation efficiency under the assumption that feedback occurs on subgrid scales, while the GASOLINE simulations have feedback which drives large scale outflows. In all cases, the marked knee-shape in mass aggregation tracks, corresponding to the transition from an early phase of rapid mass assembly to a later slower one, separates the properties of two populations within the simulated bulges. The bulges analyzed show an important early starburst resulting from the collapse-like fast phase of mass assembly, followed by a second phase with lower star formation, driven by a variety of processes such as disk instabilities and/or mergers. Classifying bulge stellar particles identified at z=0 into old and young according to these two phases, we found bulge stellar sub-populations with distinct kinematics, shapes, stellar ages and metal contents. The young components are more oblate, generally smaller, more rotationally supported, with higher metallicity and less alpha-element enhanced than the old ones. These results are consistent with the current observational status of bulges, and provide an explanation for some apparently paradoxical observations, such as bulge rejuvenation and metal-content gradients observed. Our results suggest that bulges of L* galaxies will generically have two bulge populations which can be likened to classical and pseudo-bulges, with differences being in the relative proportions of the two, which may vary due to galaxy mass and specific mass accretion and merger histories.
The interior of a neutron star is likely to be predominantly a mixture of superfluid neutrons and superconducting protons. This results in the quantisation of the star's magnetic field into an array of thin fluxtubes, producing a macroscopic force very different from the Lorentz force of normal matter. We show that in an axisymmetric superconducting equilibrium the behaviour of a magnetic field is governed by a single differential equation. Solving this, we present the first self-consistent superconducting neutron star equilibria with poloidal and mixed poloidal-toroidal fields, also giving the first quantitative results for the corresponding magnetically-induced distortions to the star. The poloidal component is dominant in all our configurations. We suggest that the transition from normal to superconducting matter in a young neutron star may cause a large-scale field rearrangement.
Accreting X-ray pulsars are among the best observed objects of X-ray
astronomy with a rich data set of observational phenomena in the spectral and
timing domain. While the general picture for these sources is well established,
the detailed physics behind the observed phenomena are often subject of debate.
We present recent observational, theoretical and modeling results for the
structure and dynamics of the accretion column in these systems. Our results
indicate the presence of different accretion regimes and possible explanations
for observed variations of spectral features with luminosity.
To study the capabilities of supernova neutrino detectors, the instantaneous spectra are often represented by a quasi-thermal distribution of the form f (E) = E^alpha e^{-(alpha+1) E/E_{av}} where E_{av} is the average energy and alpha a numerical parameter. Based on a spherically symmetric SN model with full Boltzmann neutrino transport we have, at a few representative post-bounce times, re-converged the models with vastly increased energy resolution to test the fit quality. For our examples, the spectra are well represented by such a fit in the sense that the counting rates for a broad range of target nuclei, sensitive to different parts of the spectrum, are reproduced very well. Therefore, the first few energy moments of numerical spectra hold enough information to forecast the response of multi-channel supernova neutrino detection.
This paper is the second in a series of studies working towards constructing a realistic, evolving, non-potential coronal model for the solar magnetic carpet. In the present study, the interaction of two magnetic elements is considered. Our objectives are to study magnetic energy build up, storage and dissipation as a result of emergence, cancellation, and flyby of these magnetic elements. In the future these interactions will be the basic building blocks of more complicated simulations involving hundreds of elements. Each interaction is simulated in the presence of an overlying uniform magnetic field, which lies at various orientations with respect to the evolving magnetic elements. For these three small-scale interactions, the free energy stored in the field at the end of the simulation ranges from $0.2-2.1\times 10^{26}$ ergs, while the total energy dissipated ranges from $1.3-6.3\times 10^{26}$ ergs. For all cases, a stronger overlying field results in higher energy storage and dissipation. For the cancellation and emergence simulations, motion perpendicular to the overlying field results in the highest values. For the flyby simulations, motion parallel to the overlying field gives the highest values. In all cases, the free energy built up is sufficient to explain small-scale phenomena such as X-ray bright points or nanoflares. In addition, if scaled for the correct number of magnetic elements for the volume considered, the energy continually dissipated provides a significant fraction of the quiet Sun coronal heating budget.
We report multiple epoch VLA/JVLA observations of 89 northern hemisphere sources, most with 37\,GHz flux density > 1 Jy, observed at 4.8, 8.5, 33.5, and 43.3 GHz. The high frequency selection leads to a predominantly flat spectrum sample, with 85% of our sources being in the Planck Early Release Compact Source Catalog (ERCSC). These observations allow us to: 1) validate Planck's 30 and 44 GHz flux density scale, 2) extend the radio SEDs of Planck sources to lower frequencies allowing for the full 5-857GHz regime to be studied, and 3) characterize the variability of these sources. At 30 GHz and 44 GHz, the JVLA and Planck flux densities agree to within 3%. On timescales of less than two months the median variability of our sources is 2%. On timescales of about a year the median variability increases to 14%. Using the WMAP 7-year data, the 30 GHz median variability on a 1-6 years timescale is 16%.
We present an ongoing survey with the Nan\c{c}ay Radio Telescope at L-band. The targeted area is $74^\circ \lesssim l <150^\circ$ and $3.5^\circ < |b| < 5^\circ$. This survey is characterized by a long integration time (18 min), large bandwidth (512 MHz) and high time and frequency resolution (64 $\mu$s and 0.5 MHz) giving a nominal sensitivity limit of 0.055 mJy for long period pulsars. This is about 2 times better than the mid-latitude HTRU survey, and is designed to be complementary with current large scale surveys. This survey will be more sensitive to transients (RRATs, intermittent pulsars), distant and faint millisecond pulsars as well as scintillating sources (or any other kind of radio faint sources) than all previous short-integration surveys.
Shortly after the discovery of PSR J1906+0746, some hints of profile variations were already interpreted as first signs of relativistic spin-precession occuring. Using observations from the Nan\c{c}ay, Arecibo and Green Bank Radio Observatories, we report here the measurement of pulse profile and polarimetric variations. Using the Rotating Vector Model, we show that PSR J1906+0746 is likely to be an orthogonal rotator ($\alpha \simeq 80^\circ$). Fitting our polarimetric data to a precession model, we determined the geometry of the pulsar and found a wide misalignment angle ($\delta = 89_{-44}^{+85}$ deg, 95% C.L.), although the uncertainty is large. Assuming this geometry, we constructed the beam maps of both magnetic poles.
The efficacy of the Hill stability (HS) criterion is compared to other known chaos indicators such as the maximum Lyapunov exponent (MLE) and Mean Exponential Growth factor of Nearby Orbits (MEGNO) maps. The orbits of four individual planets in four known binary star systems, \gamma Cephei, Gliese 86, HD 41004, and HD 196885, are numerically integrated using various numerical techniques to assess the chaotic or quasi-periodic nature of the dynamical system considered. The Hill stability which measures the orbital perturbation of a planet around the primary star due to the secondary star is calculated for each system. The maximum Lyapunov exponent time series are generated to measure the divergence/convergence rate of stable manifolds, which are used to differentiate between chaotic and non-chaotic orbits. Then, we calculate dynamical MEGNO maps from solving the variational equations along with the equations of motion. These maps allow us to accurately differentiate between stable and unstable dynamical systems. The results obtained from the analysis of HS, MLE, and MEGNO maps are analysed for their dynamical variations and resemblance. The qualitative efficiency of each indicator is analysed which demonstrates that HS can be used as an alternative to MLE. The HS test for the planets shows stability and quasi-periodicity for at least ten million years. The MLE and the MEGNO maps have also indicated the local quasi-periodicity and global stability in relatively short integration period. Based on our discussion, the HS criterion is found to be a comparably efficient tool to measure the stability of planetary orbits with respect to different simulation timespans.
"The investigation into the possible effects of cosmic rays on living
organisms will also offer great interest." - Victor F. Hess, Nobel Lecture,
December 12, 1936
High-energy radiation bursts are commonplace in our Universe. From nearby
solar flares to distant GRBs, a variety of physical processes accelerate
charged particles in a wide energy range, which subsequently reach the Earth.
Such particles interact with, and contribute to a number of physical processes
occurring in the Earth system. A large fraction of the energy of charged
particles gets deposited in the atmosphere, ionizing the atmosphere, causing
changes in atmospheric chemistry and affecting the global electric circuit.
Remaining secondary particles contribute to the background dose of cosmic rays
on the surface and parts of the subsurface region. Life has evolved since past
~ 3 billion years in presence of this background radiation, which itself has
varied considerably during the period [1-3]. As demonstrated by the Miller-Urey
experiment, lightning plays a very important role in the formation of complex
organic molecules, which are the building blocks of more complex structures
forming life. There is growing evidence of increase in the lightning rate with
increasing flux of charged particles. Is there a connection between enhanced
rate of cosmic rays and the origin of life? Cosmic ray secondaries are also
known to damage DNA and cause mutations, leading to cancer and other diseases.
It is now possible to compute radiation doses from secondary particles, in
particular muons and neutrons. Have the variations in cosmic ray flux affected
the evolution of life on earth? We describe the mechanisms of cosmic rays
affecting terrestrial life and review the potential implications of the
variation of high-energy astrophysical radiation on the history of life on
earth.
We study the ionized gas spectrum of star forming regions in the Holmberg II galaxy using the optical long-slit spectroscopic observations made at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). We estimate the oxygen, nitrogen, sulphur, neon, and argon abundances in individual HII regions and find the average metallicity in the galaxy to be Z=0.1 or 0.3 Zsun depending on the estimation method employed. We use these observations combined with the results of our earlier studies of the Irr galaxy IC 10 and BCD galaxy VII Zw 403 to compare the currently most popular methods of gas metallicity estimation in order to select among them the techniques that are most reliable for analysing Irr galaxies. To this end, we use the "direct" Te method and six empirical and theoretical methods. The results of our observations mostly confirm the conclusions of Lopez-Sanchez et al. (2012) based on the analysis of systematic deviations of metallicity estimates derived by applying different methods to "model" HII regions.
The catalogue of close neighbors of Markarian galaxies located inside of circles with radii 60 kpc from the centers of Markarian objects is presented, which combines extensive new measurements of their optical parameters with a literature and database search. The measurements were made using images extracted from the Digitized Sky Survey (DSS) Jpg (blue), Fpg (red) and Ipg (near-infrared) band photographic plates. We provide names, accurate coordinates, redshifts, morphological types, blue, red and near-infrared apparent magnitudes, apparent blue major diameters, axial ratios, as well as position angles for the neighbor galaxies. We also include their 2MASS infrared magnitudes. The total number of Markarian galaxies in the database is 274 and number of their neighbors is 359. The physical parameters of the systems of Markarian galaxies and their neighbors are determined and presented.
The sizes of galaxies are known to be closely related with their masses, luminosities, redshifts and morphologies. However, when we fix these quantities and morphology, we still find large dispersions in the galaxy size distribution. We investigate the origin of these dispersions for red early-type galaxies, using two SDSS-based catalogs. We find that the sizes of faint galaxies (log(M_dyn/M_sun) < 10.3 or M_r > -19.5, where M_r is the r-band absolute magnitude, k-corrected to z = 0.1) are affected more significantly by luminosity, while the sizes of bright galaxies (log(M_dyn/M_sun) > 11.4 or M_r < -21.4) are by dynamical mass. At fixed mass and luminosity, the sizes of low-mass galaxies (log(M_dyn/M_sun) ~ 10.45 and M_r ~ -19.8) are relatively less sensitive to their colors, color gradients and axis ratios. On the other hand, the sizes of intermediate-mass (log(M_dyn/M_sun) ~ 10.85 and M_r ~ -20.4) and high-mass (log(M_dyn/M_sun) ~ 11.25 and M_r ~ -21.0) galaxies significantly depend on those parameters, in the sense that larger red early-type galaxies have bluer colors, more negative color gradients (bluer outskirts) and smaller axis ratios. These results indicate that the sizes of intermediate- and high-mass red early-type galaxies are significantly affected by their recent minor mergers or rotations, whereas the sizes of low-mass red early-type galaxies are affected by some other mechanisms. Major dry mergers also seem to have influenced on the size growth of high-mass red early-type galaxies.
We report on the small scale (0.5<r<40h^-1 Mpc) clustering of 78895 massive (M*~10^11.3M_sun) galaxies at 0.2<z<0.4 from the first two years of data from the Baryon Oscillation Spectroscopic Survey (BOSS), to be released as part of SDSS Data Release 9 (DR9). We describe the sample selection, basic properties of the galaxies, and caveats for working with the data. We calculate the real- and redshift-space two-point correlation functions of these galaxies, fit these measurements using Halo Occupation Distribution (HOD) modeling within dark matter cosmological simulations, and estimate the errors using mock catalogs. These galaxies lie in massive halos, with a mean halo mass of 5.2x10^13 h^-1 M_sun, a large scale bias of ~2.0, and a satellite fraction of 12+/-2%. Thus, these galaxies occupy halos with average masses in between those of the higher redshift BOSS CMASS sample and the original SDSS I/II LRG sample.
We present 11 candidate late-type companions to nearby stars identified with data from the Wide-field Infrared Survey Explorer (WISE) and the Two Micron All-Sky Survey (2MASS). Eight of the candidates are likely to be companions based on their common proper motions with the primaries. The remaining three objects are rejected as companions, one of which is a free-floating T7 dwarf. Spectral types are available for five of the companions, which consist of M2V, M8.5V, L5, T8, and T8. Based on their photometry, the unclassified companions are probably two mid-M dwarfs and one late-M/early-L dwarf. One of the T8 companions, WISE J142320.84+011638.0, has already been reported by Pinfield and coworkers. The other T8 companion, ULAS J095047.28+011734.3, was discovered by Burningham and coworkers through the United Kingdom Infrared Telescope Infrared Deep Sky Survey, but its companionship has not been previously recognized in the literature. The L5 companion, 2MASS J17430860+8526594, is a new member of a class of L dwarfs that exhibit unusually blue near-IR colors. Among the possible mechanisms that have been previously proposed for the peculiar colors of these L dwarfs, low metallicity does not appear to be a viable explanation for 2MASS J17430860+8526594 since our spectrum of the primary suggests that its metallicity is not significantly subsolar.
Black hole masses are estimated for radio-loud quasars using several self-consistent scaling relationships based on emission-line widths and continuum luminosities. The emission lines used, H-beta, Mg II, and C IV, have different dependencies on orientation as estimated by radio core dominance. We compare differences in the log of black hole masses estimated from different emission lines and show that they depend on radio core dominance in the sense that core-dominated, jet-on objects have systematically smaller H-beta and Mg II determined masses compared to those from C IV, while lobe-dominated edge-on objects have systematically larger H-beta and Mg II determined masses compared to those from C IV. The effect is consistent with the H-beta line width, and to a lesser extent that of Mg II, being dependent upon orientation in the sense of a axisymmetric velocity field plus a projection effect. The size of the effect is nearly an order of magnitude in black hole mass going from one extreme orientation to the other. We find that radio spectral index is a good proxy for radio core dominance and repeating this analysis with radio spectral index yields similar results. Accounting for orientation could in principle significantly reduce the scatter in black hole mass scaling relationships, and we quantify and offer a correction for this effect cast in terms of radio core dominance and radio spectral index.
We develop an analytical model for the accretion and gravitational drag on a point mass that moves hypersonically in the midplane of a gaseous disk with a Gaussian vertical density stratification. Such a model is of interest for studying the interaction between a planet and a protoplanetary disk, as well as the dynamical decay of massive black holes in galactic nuclei. The model considers that the flow is ballistic, and gives fully analytical expressions for both the accretion rate onto the point mass, and the gravitational drag it suffers. The expressions are further simplified by taking the limits of a thick, and of a thin disk. The results for the thick disk reduce correctly to those for a uniform density environment (Cant\'o et al. 2011). We find that for a thin disk (small vertical scaleheight compared to the gravitational radius) the accretion rate is proportional to the mass of the moving object and to the surface density of the disk, while the drag force is independent of the velocity of the object. The gravitational deceleration of the hypersonic perturber in a thin disk was found to be independent of its parameters (i.e. mass or velocity) and depends only on the surface mass density of the disk. The predictions of the model are compared to the results of three-dimensional hydrodynamical simulations, with a reasonable agreement.
Predicting the rate of escape and thermal structure of Pluto's upper atmosphere in preparation for the New Horizons Spacecraft encounter in 2015 is important for planning and interpreting the expected measurements. Having a moderate Jeans parameter Pluto's atmosphere does not fit the classic definition of Jeans escape for light species escaping from the terrestrial planets, nor does it fit the hydrodynamic outflow from comets and certain exoplanets. It has been proposed for some time that Pluto lies in the region of slow-hydrodynamic escape. Using a hybrid fluid/molecular-kinetic model, we previously demonstrated the typical implementation of this model fails to correctly describe the appropriate temperature structure for the upper atmosphere for solar minimum conditions. Here we used a time-dependent solver to allow us to extend those simulations to higher heating rates and we examined fluid models in which Jeans-like escape expressions are used for the upper boundary conditions. We compare these to our hybrid simulations of the atmosphere under heating conditions roughly representative of solar minimum and medium conditions as these bracket conditions expected during the New Horizon encounter. Although we find escape rates comparable to those previously estimated by the slow-hydrodynamic escape model, and roughly consistent with energy limited escape, our model produces a much more extended atmosphere with higher temperatures roughly consistent with recent observations of CO. Such an extended atmosphere will be affected by Charon and will affect Pluto's interaction with the solar wind at the New Horizon encounter. Since we showed earlier that such models can be scaled, these results have implications for modeling exoplanet atmospheres for which the energy limited escape approximation is often used.
We present results from our analysis of Chandra X-ray Observatory, W. M. Keck Observatory, and Karl G. Jansky Very Large Array (VLA) images of the Crab Nebula that were contemporaneous with the gamma-ray flare of 2011 April. Despite hints in the X-ray data, we find no evidence for statistically significant variations that pinpoint the specific location of the flares within the Nebula. The Keck observations extend this conclusion to the "inner knot", i.e., the feature within an arcsecond of the pulsar. The VLA observations support this conclusion. We also discuss theoretical implications of the gamma-ray flares and suggest that the most dramatic gamma-ray flares are due to radiation-reaction-limited synchrotron emission associated with sudden, dissipative changes in the current system sustained by the central pulsar.
Since Edwin Hubble introduced his famous tuning fork diagram more than 70 years ago, spiral galaxies and early-type galaxies (ETGs) have been regarded as two distinct families. The spirals are characterized by the presence of disks of stars and gas in rapid rotation, while the early-types are gas poor and described as spheroidal systems, with less rotation and often non-axisymmetric shapes. The separation is physically relevant as it implies a distinct path of formation for the two classes of objects. I will give an overview of recent findings, from independent teams, that motivated a radical revision to Hubble's classic view of ETGs. These results imply a much closer link between spiral galaxies and ETGs than generally assumed.
Quantum gravity theory is untested experimentally. Could it be tested with tabletop experiments? While the common feeling is pessimistic, a detailed inquiry shows it possible to sidestep the onerous requirement of localization of a probe on Planck length scale. I suggest a tabletop experiment which, given state of the art ultrahigh vacuum and cryogenic technology, could already be sensitive enough to detect Planck scale signals. The experiment combines a single photon's degree of freedom with one of a macroscopic probe to test Wheeler's conception of "spacetime foam", the assertion that on length scales of the order Planck's, spacetime is no longer a smooth manifold. The scheme makes few assumptions beyond energy and momentum conservations, and is not based on a specific quantum gravity scheme.
We shall consider the problem of Dark Matter in torsion gravity with Dirac matter fields: we will consider the fact that if WIMP in a bath are allowed to form condensates then torsional effects may be relevant even at galactic scales; we show that torsionally-gravitating Dirac fields have interesting features for the problem of DM. We discuss some consequences.
We extend our investigation of the IR effects on the local dynamics of matter fields in quantum gravity. Specifically we clarify how the IR effects depend on the change of the quantization scheme: different parametrization of the metric and the matter field redefinition. An arbitrary choice of the parametrization of the metric and the matter field redefinition do not preserve the Lorentz invariance of the local dynamics. As for the effect of different parametrization of the metric alone, the Lorentz symmetry breaking term can be eliminated by shifting the background metric. In contrast, we cannot compensate the matter field redefinition dependence by such a way. The Lorentz invariance can be retained only when we adopt the specific matter field redefinitions where all dimensionless couplings become scale invariant at the classical level.
This paper is a direct continuation of our old publication where it was found the exact solution of the Einstein-Maxwell equations for two static sources of Reissner-Nordstrom type in the state of the physical equilibrium. Here we present the exact solution of these equations for the case of two rotating charged sources and we proved the existence of the physical equilibrium state also for this general case.
Experiments at electron-positron colliders can search for dark matter particle pair-production in association with a photon. We estimate the sensitivity of this search at the proposed International Linear Collider (ILC), under a variety of run scenarios. We employ the effective operator formalism to provide a quasi-model-independent theoretical description of the signal, and present the reach of the ILC in terms of the scale \Lambda suppressing the dark matter-electron coupling operator. We find that at the 250 GeV center-of-mass energy, the ILC can probe \Lambda up to 1-1.2 TeV, a factor of 2.5-3 above the best current bounds from LEP-2. With 1 TeV energy and polarized beams, the reach can be extended to 3-4 TeV. The ILC can discover this signature even if annihilation to electrons provides only a small fraction of the total dark matter annihilation rate in the early universe. We also argue that large regions of parameter space allowed by current LHC and direct detection bounds will be accessible at the ILC.
F-term hybrid inflation (FHI) of the hilltop type can generate a scalar spectral index, ns, in agreement with the fitting of the seven-year Wilkinson microwave anisotropy probe data by the standard power-law cosmological model with cold dark matter and a cosmological constant, LambdaCDM. We investigate the realization of this type of FHI by using quasi-canonical Kahler potentials with or without the inclusion of extra hidden-sector fields. In the first case, acceptable results can be obtained by constraining the coefficients of the quadratic and/or quartic supergravity correction to the inflationary potential and therefore a mild tuning of the relevant term of the Kahler potential is unavoidable. Possible reduction of ns without generating maxima and minima of the potential on the inflationary path is also possible in a limited region of the available parameter space. The tuning of the terms of the Kahler potential can be avoided with the adoption of a simple class of string-inspired Kahler potentials for the hidden-sector fields which ensures a resolution to the eta problem of FHI and allows acceptable values for the spectral index, constraining the coefficient of the quartic supergravity correction to the inflationary potential. Performing a four-point test of the analyzed models, we single out the most promising of these.
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Classical Cepheids remain a cornerstone of the cosmic distance scale, and thus characterizing the dependence of their light amplitude on metallicity is important. Period-amplitude diagrams constructed for longer-period classical Cepheids in IC 1613, NGC 3109, SMC, NGC 6822, LMC, and the Milky Way imply that very metal-poor Cepheids typically exhibit smaller V-band amplitudes than their metal-rich counterparts. The results provide an alternate interpretation relative to arguments for a null and converse metallicity dependence. The empirical results can be employed to check predictions from theoretical models, to approximate mean abundances for target populations hosting numerous long-period Cepheids, and to facilitate the identification of potentially blended or peculiar objects.
We present results from a total of 459 repeated 3.1 GHz radio continuum
observations (of which 379 were used in a search for transient sources) of the
ELAIS-N1, Coma, Lockman Hole, and NOAO Deep Wide Field Survey fields as part of
the Pi GHz Sky Survey (PiGSS). The observations were taken approximately once
per day between 2009 May and 2011 April. Each image covers 11.8 square degrees
and has 100 arcsecond FWHM resolution. Deep images for each of the four fields
have rms noise between 180 and 310 uJy and the corresponding catalogs contain
~200 sources in each field. Typically 40 - 50 of these sources are detected in
each single-epoch image. This represents one of the shortest cadence, largest
area, multi-epoch surveys undertaken at these frequencies.
We compare the catalogs generated from the combined images to those from
individual epochs, and from monthly averages, as well as to legacy surveys. We
undertake a search for transients, with particular emphasis on excluding false
positive sources. We find no confirmed transients, defined here as sources that
can be shown to have varied by at least a factor 10. However, we find one
source which brightened in a single-epoch image to at least six times the upper
limit from the corresponding deep image. We also find a source associated with
a z = 0.6 quasar which appears to have brightened by a factor of about three in
one of our deep images, when compared to catalogs from legacy surveys.
We place new upper limits on the number of transients brighter than 10 mJy:
fewer than 0.08 transients / sq. deg. with characteristic timescales of months
to years; fewer than 0.02 / sq. deg. with timescales of months; and fewer than
0.009 / sq. deg with timescales of days. We also plot upper limits as a
function of flux density for transients on the same timescales.
Precise exoplanet characterization requires precise classification of exoplanet host stars. The masses of host stars are commonly estimated by comparing their spectra to those predicted by stellar evolution models. However, spectroscopically determined properties are difficult to measure accurately for stars that are substantially different from the Sun, such as M-dwarfs and evolved stars. Here, we propose a new method to dynamically measure the masses of transiting planets near mean-motion resonances and their host stars by combining observations of transit timing variations with radial velocity measurements. We derive expressions to analytically determine the mass of each member of the system and demonstrate the technique on the Kepler-18 system. We compare these analytic results to numerical simulations and find the two are consistent. We identify eight systems for which our technique could be applied if follow-up radial velocity measurements are collected. We conclude this analysis would be optimal for systems discovered by next generation missions similar to TESS or PLATO, which will target bright stars that are amenable to efficient RV follow-up.
Context. Brown dwarfs represent a sizable fraction of the stellar content of our Galaxy and populate the transition between the stellar and planetary mass regime. There is however no agreement on the processes responsible for their formation. Aims. We have conducted a large survey of the young, nearby cluster IC 348, to uncover its low-mass brown dwarf population and study the cluster properties in the substellar regime. Methods. Deep optical and near-IR images taken with MegaCam and WIRCam at the Canada-France-Hawaii Telescope (CFHT) were used to select photometric candidate members. A spectroscopic follow-up of a large fraction of the candidates was conducted to assess their youth and membership. Results. We confirmed spectroscopically 16 new members of the IC 348 cluster, including 13 brown dwarfs, contributing significantly to the substellar census of the cluster, where only 30 brown dwarfs were previously known. Five of the new members have a L0 spectral type, the latest-type objects found to date in this cluster. At 3 Myr, evolutionary models estimate these brown dwarfs to have a mass of ~13 Jupiter masses. Combining the new members with previous census of the cluster, we constructed the IMF complete down to 13 Jupiter masses. Conclusions. The IMF of IC 348 is well fitted by a log-normal function, and we do not see evidence for variations of the mass function down to planetary masses when compared to other young clusters.
As atoms formed for the first time during primordial recombination, they emitted bound-bound and free-bound radiation leading to spectral distortions to the cosmic microwave background. These distortions might become observable in the future with high-sensitivity spectrometers, and provide a new window into physical conditions in the early universe. The standard multilevel atom method habitually used to compute the recombination spectrum is computationally expensive, impeding a detailed quantitative exploration of the information contained in spectral distortions thus far. In this work it is shown that the emissivity in optically thin allowed transitions can be factored into a computationally expensive but cosmology-independent part and a computationally cheap, cosmology-dependent part. The slow part of the computation consists in pre-computing temperature-dependent effective "conductances", linearly relating line or continuum intensity to departures from Saha equilibrium of the lowest-order excited states (2s and 2p), that can be seen as "voltages". The computation of these departures from equilibrium as a function of redshift is itself very fast, thanks to the effective multilevel atom method introduced in an earlier work. With this factorization, the recurring cost of a single computation of the recombination spectrum is only a fraction of a second on a standard laptop, more than four orders of magnitude shorter than standard computations. The spectrum from helium recombination can be efficiently computed in an identical way, and a fast code computing the full primordial recombination spectrum with this method will be made publicly available soon.
A hybrid JHKs-W1W2W3W4 high-spectral index (alpha) selection scheme was employed to identify (sub)clusters of class I/f candidate protostars (YSOs) in WISE observations (the Wide-Field Infrared Survey Explorer). n>10^4 candidate YSOs were detected owing to WISE's advantageous all-sky spatial coverage, and a subsample (n~200) of their heavily-obscured host (sub)clusters were correlated with the Avedisova (2002) and Dias et al. (2002) catalogs of star-forming regions. Forthcoming observations from the VVV/UKIDSS surveys shall facilitate the detection of additional protostars and bolster efforts to delineate the Galactic plane, since the campaigns aim to secure deep JHKs photometry for a pertinent fraction of the WISE targets lacking 2MASS detections, and to provide improved data for YSOs near the limits of the 2MASS survey.
We present X-ray and multiwavelength studies of a sample of eight high-luminosity active galactic nuclei (AGNs) with disc-like H\beta emission-line profiles selected from the Sloan Digital Sky Survey Data Release 7. These sources have higher redshift (z~0.6) than the majority of the known disc-like emitters, and they occupy a largely unexplored space in the luminosity-redshift plane. Seven sources have typical AGN X-ray spectra with power-law photon indices of \Gamma~1.4-2.0; two of them show some X-ray absorption (column density N_H~10^{21}-10^{22} cm^{-2}$ for neutral gas). The other source, J0850+4451, has only three hard X-ray photons detected and is probably heavily obscured (N_H>3x10^{23} cm^{-2}). This object is also identified as a low-ionization broad absorption line (BAL) quasar based on Mg II \lambda2799 absorption; it is the first disc-like emitter reported that is also a BAL quasar. The IR-to-UV spectral energy distributions (SEDs) of these eight sources are similar to the mean SEDs of typical quasars with a UV "bump", suggestive of standard accretion discs radiating with high efficiency, which differs from low-luminosity disc-like emitters. Studies of the X-ray-to-optical power-law slope parameters (\alpha_{OX}) indicate that there is no significant excess X-ray emission in these high-luminosity disc-like emitters. Energy budget analysis suggests that for disc-like emitters in general, the inner disc must illuminate and ionize the outer disc efficiently (~15% of the nuclear ionizing radiation is required on average) via direct illumination and/or scattering. Warped accretion discs are probably needed for direct illumination to work in high-luminosity objects, as their geometrically thin inner discs decrease the amount of direct illumination possible for a flat disc.
In this paper, we consider dynamical behavior of astrophysical objects such as galaxies and dwarf galaxies taking into account both the gravitational attraction between them and the cosmological expansion of the Universe. First, we obtain the general system of equations and apply them to some abstract systems of galaxies. Then we investigate the collision between the Milky Way and Andromeda in future. We demonstrate that for currently known parameters of this system the collision is hardly possible because of the angular momentum. These galaxies will approach the minimum distance of about 290 Kpc in 4.44 Gyr from present, and then begin to run away irreversibly from each other. We also define the region in the vicinity of our Local Group where the formation of the Hubble flows starts. For such processes, the zero-acceleration surface (where the gravitational attraction is balanced by the cosmological accelerated expansion) plays the crucial role. We show that such surface is absent for the Local Group. Instead, we find two points and one circle with zero acceleration. Nevertheless, there is a nearly closed area around the MW and M31 where the absolute value of the acceleration is approximately equal to zero. The Hubble flows are formed outside of this area.
The NASA Exoplanet Science Institute (NExScI) hosts the annual Sagan Workshops, thematic meetings aimed at introducing researchers to the latest tools and methodologies in exoplanet research. The theme of the Summer 2012 workshop, held from July 23 to July 27 at Caltech, was to explore the use of exoplanet light curves to study planetary system architectures and atmospheres. A major part of the workshop was to use hands-on sessions to instruct attendees in the use of three open source tools for the analysis of light curves, especially from the Kepler mission. Each hands-on session involved the 160 attendees using their laptops to follow step-by-step tutorials given by experts. We describe how we used the Amazon Elastic Cloud 2 to run these applications.
Large scale surveys of the prominent members of the Local Group have provided compelling evidence for the hierarchical formation of massive galaxies, revealing a wealth of substructure that is thought to be the debris from ancient and on-going accretion events. In this paper, we compare two extant surveys of the M31-M33 subgroup of galaxies; the Pan-Andromeda Archaeological Survey (PAndAS) of the stellar structure, and a combination of observations of the HI gaseous content, detected at 21cm. Our key finding is a marked lack of spatial correlation between these two components on all scales, with only a few potential overlaps between stars and gas.The paucity of spatial correlation significantly restricts the analysis of kinematic correlations, although there does appear to the HI kinematically associated with the Giant Stellar Stream where it passes the disk of M31. These results demonstrate that that different processes must significantly influence the dynamical evolution of the stellar and HI components of substructures, such as ram pressure driving gas away from a purely gravitational path. Detailed modelling of the offset between the stellar and gaseous substructure will provide a determination of the properties of the gaseous halo of M31 and M33.
Theoretical $\Lambda$CDM cosmological models predict a much larger number of low mass dark matter haloes than has been observed in the Local Group of galaxies. One possible explanation is the increased difficulty of detecting these haloes if most of the visible matter is lost at early evolutionary phases through galactic winds. In this work we study the current models of triggering galactic winds in dwarf spheroidal galaxies (dSph) from supernovae, and study, based on 3D hydrodynamic numerical simulations, the correlation of the mass loss rates and important physical parameters as the dark matter halo mass and its radial profile, and the star formation rate. We find that the existence of winds is ubiquitous, independent on the gravitational potential. Our simulations revealed that the Rayleigh-Taylor Instability (RTI) may play a major role on pushing matter out of these systems, even for very massive haloes. The instability is responsible for 5 - 40% of the mass loss during the early evolution of the galaxy, being less relevant at $t > 200$Myrs. There is no significant difference in the mass loss rates obtained for the different dark matter profiles studied (NFW and logarithmic). We have also found a correlation between the mass loss rate and both the halo mass and the rate of supernovae, as already reported in previous works. Besides, the epoch in which most of the baryon galactic matter is removed from the galaxy varies depending on the SN rate and gravitational potential. The later, combined to the importance of the RTI in each model, may change our understanding about the chemical evolution of dwarf galaxies, as well as in the heavy element contamination of the intergalactic medium at high redshifts.
We present multi-wavelength analysis around mid-infrared bubble N14 to probe the signature of triggered star formation as well as the formation of new massive star(s) and/or cluster(s) on the borders of the bubble by the expansion of the H II region. Spitzer-IRAC ratio maps reveal that the bubble is traced by the polycyclic aromatic hydrocarbon emission following an almost circular morphology except in the south-west direction towards the low molecular density environment. The observational signatures of the collected molecular and cold dust material have been found around the bubble. We have detected 418 YSOs in the selected region around the bubble N14. Interestingly, the detected YSO clusters are associated with the collected molecular and cold dust material on the borders of the bubble. One of the clusters is found with deeply embedded intermediate mass and massive Class I YSOs associated with one of the dense dust clumps in the east of the bubble N14. We do not find a good agreement between the dynamical age of the H II region and the fragmentation time of the accumulated molecular materials to explain possible "collect-and-collapse" process around the bubble N14. Therefore, we suggest the possibility of triggered star formation by compression of the pre-existing dense clumps by the shock wave and/or small scale Jeans gravitational instabilities in the collected materials. We have also investigated 5 young massive embedded protostars (8 to 10 M_sun) and 15 intermediate mass (3 to 7 M_sun) Class I YSOs which are associated with the dust and molecular fragmented clumps at the borders of the bubble. We conclude that the expansion of the H II region is also leading to the formation of these intermediate and massive Class I YSOs around the bubble N14.
We observe a solar surge in NOAA AR11271 using SDO AIA 304 image data on 25 August, 2011. The surge rises vertically from its origin upto a height of 65 Mm with a terminal velocity of 100 km/s, and thereafter falls and fades gradually. The total life time of the surge was 20 min. We also measure the temperature and density distribution of the observed surge during its maximum rise, and found an average temperature and density of 2.0 MK and 4.1 x 109 cm-3, respectively. The temperature map shows the expansion and mixing of cool plasma lagging behind the hot coronal plasma along the surge. As SDO/HMI temporal image data does not show any detectable evidence of the significant photospheric magnetic field cancellation for the formation of the observed surge, we infer that it is probably driven by magnetic reconnection generated thermal energy in the lower chromosphere. The radiance (thus mass density) oscillations near the base of the surge are also evident, which may be the most likely signature of its formation by a reconnection generated pulse. In support of the present observational base-line of the triggering of the surge due to chromospheric heating, we devise a numerical model with conceivable implementation of VAL-C atmosphere and a thermal pulse as an initial trigger. We find that the pulse steepens into a slow shock at higher altitudes that triggers plasma perturbations exhibiting the observed features of the surge, e.g., terminal velocity, height, width, life-time, and heated fine structures near its base.
The triple asteroids and triple Kuiper belt objects (collectively called the triple minor planets) in the Solar system are of particular interest to the scientific community since the discovery of the first triple asteroid system in 2004. In this paper, the Hill stability of the nine known triple minor planets in the Solar system is investigated. Seven of the systems are of large size ratio, i.e. they consist of a larger primary and two moonlets, while the other two systems have components of comparable size. Each case is treated separately. For the triple minor planets that have large size ratio, the sufficient condition for Hill stability is expressed in closed form. This is not possible for the systems with comparable size components, for which the Hill stability is assessed by a combination of analytical and numerical means. It is found that all the known triple minor planets are Hill stable, except 3749 Balam, for which the incomplete orbital parameters make the Hill stability of the system uncertain. This suggests that there might be more such stable triple minor planets in the Solar system yet to be observed. It is also shown that the Hill stability regions increase as the mutual inclination between the inner orbit and outer orbit decreases, the semimajor axis ratio of the inner orbit with respect to the outer orbit decreases, and the mass ratio of the outer satellite with respect to the inner satellite increases. This study therefore provides useful information about dynamical properties of the triple minor planets in the Solar system.
Maxima of the linear density field form a point process that can be used to understand the spatial distribution of virialized halos that collapsed from initially overdense regions. However, owing to the peak constraint, clustering statistics of discrete density peaks are difficult to evaluate. For this reason, local bias schemes have received considerably more attention in the literature thus far. In this paper, we show that the 2-point correlation function of maxima of a homogeneous and isotropic Gaussian random field can be thought of, up to second order at least, as arising from a local bias expansion formulated in terms of rotationally invariant variables. This expansion relies on a unique smoothing scale, which is the Lagrangian radius of dark matter halos. The great advantage of this local bias approach is that it circumvents the difficult computation of joint probability distributions. We demonstrate that the bias factors associated with these rotational invariants can be computed using a peak-background split argument, in which the background perturbation shifts the corresponding probability distribution functions. Consequently, the bias factors are orthogonal polynomials averaged over those spatial locations that satisfy the peak constraint. In particular, asphericity in the peak profile contributes to the clustering at quadratic and higher order, with bias factors given by generalized Laguerre polynomials. We speculate that our approach remains valid at all orders, and that it can be extended to describe clustering statistics of any point process of a Gaussian random field. Our results will be very useful to model the clustering of discrete tracers with more realistic collapse prescriptions involving the tidal shear for instance.
Three of the most important and most puzzling features of the Sun's atmosphere are the smoothness of the closed field corona, the accumulation of magnetic shear at photospheric polarity inversion lines (PIL), and the complexity of the slow wind. We propose that a single process, helicity condensation, is the physical mechanism giving rise to all three features. A simplified model is presented for how helicity is injected and transported in the closed corona by magnetic reconnection. With this model we demonstrate that helicity must condense onto PILs and coronal hole boundaries, and estimate the rate of helicity accumulation at PILs and the loss to the wind. Our results can account for many of the observed properties of the closed corona and wind.
The non-modal self-heating mechanism driven by the velocity shear in kinematically complex magnetohydrodynamic (MHD) plasma flows is considered. The study is based on the full set of MHD equations including dissipative terms. The equations are linearized and unstable modes in the flow are looked for. Two different cases are specified and studied: (a) the instability related to an exponential evolution of the wave vector; and (b) the parametric instability, which takes place when the components of the wave vector evolve in time periodically. By examining the dissipative terms, it is shown that the self-heating rate provided by viscous damping is of the same order of magnitude as that due to the magnetic resistivity. It is found that the heating efficiency of the exponential instability is higher than that of the parametric instability.
We report the first identification of the optical bands of the B-X system of AlO in the red supergiant VY CMa. In addition to TiO, VO, ScO, and YO, which were recognized in the optical spectrum of the star long time ago, AlO is another refractory molecule which displays strong emission bands in this peculiar star. Simulating the bands of AlO, we derive a rotational temperature of the circumstellar gas of Trot=700K. By resolving individual rotational components of the bands, we derive the kinematical characteristics of the gas, finding that the emission is centered at the stellar radial velocity and its intrinsic width is 13.5 km/s (full width at half maximum). It is the narrowest emission among all (thermal) features observed in VY CMa so far. The temperature and line widths suggest that the emission arises in gas located within ~20 stellar radii, where the outflow is still being accelerated. This result contradicts equilibrium-chemistry models which predict substantial AlO abundances only to within a few stellar radii. We argue that non-equilibrium models involving propagation of shocks are needed to explain the observations.
The early B supergiant LMC star BI 108 is photometrically variable with a unique light curve; two strong periods are present in an almost precise 3:2 resonance. We collected spectroscopic data at VLT/UVES, sampling the supercycle of 10.733 days in ten epochs. We find spectral signatures for a SB2 system consisting of two massive B1 supergiants orbiting at the orbital period of 5.366 days. The shorter periodicity resembles the light curve of an eclipsing binary with periodicity 3.578 days that is not detected in the data. We discuss possible causes for the short periodicity and conclude that the quadruple system is the more plausible hypothesis.
The discovery of ubiquitous low-frequency (3-5mHz) Alfvenic waves in the solar chromosphere (with Hinode/SOT), and corona (with CoMP and the Solar Dynamics Observatory, SDO) has provided some insight into the non-thermal energy content of the outer solar atmosphere. However, many questions remain about the true magnitude of the energy flux carried by these waves. Here we explore the apparent discrepancy in the resolved coronal Alfvenic wave amplitude (~0.5km/s) measured by the Coronal Multi-channel Polarimeter (CoMP) compared to those of the Hinode and the SDO near the limb (~20km/s). We use a blend of observational data and a simple forward model of Alfvenic wave propagation to resolve this discrepancy and determine the Alfvenic wave energy content of the corona. Our results indicate that enormous line-of-sight superposition within the coarse spatio-temporal sampling of CoMP hides the strong wave flux observed by Hinode and SDO and leads to the large non-thermal line broadening observed. While this scenario has been assumed in the past, our observations with CoMP of a strong correlation between the non-thermal line broadening with the low amplitude, low frequency Alfvenic waves observed in the corona provide the first direct evidence of a wave-related non-thermal line broadening. By reconciling the diverse measurements of Alfvenic waves we establish large coronal non-thermal linewidths as direct signatures of the hidden, or "dark", energy content in the corona, and provide preliminary constraints on the energy content of the wave motions observed.
The very small braking index of PSR J1734-3333, $n=0.9\pm0.2$, challenges the current braking mechanisms of pulsars. We present a possible interpretation that this pulsar is surrounded by a fall-back disk and braked by the disk. We analyzed the interaction between the neutron star magnetosphere and a possible fall-back disk, and found that the braking index of the neutron star is very small in the middle stage of propeller phase. In this regime, the braking index of PSR J1734-3333 will increase in the later stage of propeller phase, when it evolves to the region of anomalous X-ray pulsars and soft gamma repeaters in the $P-\dot{P}$ diagram. The mass of the disk around PSR J1734-3333 in our model is about $20-30M_{\oplus}$, similar to the observed disk mass around AXP 4U 0142+61.
Planetary nebulae (PNe) have diverse morphological shapes, including point-symmetric and multipolar structures. Many PNe also have complicated internal structures such as torus, lobes, knots, and ansae. A complete accounting of all the morphological structures through physical models is difficult. A first step toward such an understanding is to derive the true three-dimensional structure of the nebulae. In this paper, we show that a multipolar nebula with three pairs of lobes can explain many of such features, if orientation and sensitivity effects are taken into account. Using only six parameters - the inclination and position angles of each pair - we are able to simulate the observed images of 20 PNe with complex structures. We suggest that the multipolar structure is an intrinsic structure of PNe and the statistics of multipolar PNe has been severely underestimated in the past.
The galaxy M51 was observed using the Mimir instrument on the Perkins telescope to constrain the resolved H-band (1.6 $\mu$m) polarization across the galaxy. These observations place an upper limit of $P_H<0.05%$ on the $H$-band polarization across the face of M51, at 0.6 arcsecond pixel sampling. Even with smoothing to coarser angular resolutions, to reduce polarization uncertainty, the $H$-band polarization remains undetected. The polarization upper limit at $H$-band, when combined with previous resolved optical polarimetry, rules out a Serkowski-like polarization dependence on wavelength. Other polarization mechanisms cannot account for the observed polarization ratio ($P_H/P{VRI} \lesssim 0.05$) across the face of M51.
We use 21 Hubble parameter versus redshift data points, from Gazta\~{n}aga et al. (2009), Stern et al. (2010), and Moresco et al. (2012), to place constraints on model parameters of constant and time-evolving dark energy cosmologies. This is the largest set of H(z) data considered to date. The inclusion of the 8 new Moresco et al. (2012) measurements results in H(z) constraints more restrictive than those derived by Chen & Ratra (2011b). These constraints are now almost as restrictive as those that follow from current Type Ia supernova (SNIa) apparent magnitude versus redshift data (Suzuki et al. 2012), which now more carefully account for systematic uncertainties. This is a remarkable result. We emphasize however that SNIa data have been studied for a longer time than the H(z) data, possibly resulting in a better estimate of potential systematic errors in the SNIa case. A joint analysis of the H(z), baryon acoustic oscillation peak length scale, and SNIa data favors a spatially-flat cosmological model currently dominated by a time-independent cosmological constant but does not exclude slowly-evolving dark energy.
We investigate the effect of the "high-pass filter" data reduction technique on the Herschel PACS PSF and noise of the PACS maps at the 70, 100 and 160 um bands and in medium and fast scan speeds. This branch of the PACS Photometer pipeline is the most used for cosmological observations and for point-source observations.The calibration of the flux loss due to the median removal applied by the PACS pipeline (high-pass filter) is done via dedicated simulations obtained by "polluting" real PACS timelines with fake sources at different flux levels. The effect of the data reduction parameter settings on the final map noise is done by using selected observations of blank fields with high data redundancy. We show that the running median removal can cause significant flux losses at any flux level. We analyse the advantages and disadvantages of several masking strategies and suggest that a mask based on putting circular patches on prior positions is the best solution to reduce the amount of flux loss. We provide a calibration of the point-source flux loss for several masking strategies in a large range of data reduction parameters, and as a function of the source flux. We also show that, for stacking analysis, the impact of the high-pass filtering effect is to reduce significantly the clustering effect. The analysis of the global noise and noise components of the PACS maps shows that the dominant parameter in determining the final noise is the high-pass filter width. We also provide simple fitting functions to build the error map from the coverage map and to estimate the cross-correlation correction factor in a representative portion of the data reduction parameter space.
We present results of a search for variable stars in the intermediate-age open cluster NGC 7044. We found 23 variable stars in the observed field. One star turned out to be of the delta Sct type with two pulsational modes excited. From the position in the color-magnitude diagram we conclude that this star is a member of the cluster. Moreover, we found 13 eclipsing systems, of which five are W UMa stars, one is a beta Lyr variable, six are beta Per binaries showing detached configuration, and the last one is another probable beta Per system. Using the period-luminosity-color relation for W UMa stars we established the membership of the contact binaries, finding four of them to be very probable cluster members. We estimated from these four stars an apparent distance modulus (m-M)_V of NGC 7044 to be 14.2 +/- 0.4 mag, which is smaller than previous determinations of this parameter. We were able to derive orbital period for only four beta Per systems. For the remaining ones we observed only two or three eclipses. Finally, nine stars we found to show irregular light changes. Most of them are red stars not belonging to the cluster. For the cluster core we determined a reddening map, which allowed us to construct a dereddened color-magnitude diagram of NGC 7044 with a narrow main-sequence. By fitting a theoretical isochrone to this diagram we derived E(V-I_C) = 0.92 mag, (m-M)_V = 14.45 mag and log(age/yr) = 9.2.
We have performed new wide-field photometry of the young open cluster NGC
6231 to study the shape of the initial mass function (IMF) and mass
segregation. We also investigated the reddening law toward NGC 6231 from
optical to mid-infrared color excess ratios, and found that the
total-to-selective extinction ratio is Rv = 3.2, which is very close to the
normal value. But many early-type stars in the cluster center show large color
excess ratios. We derived the surface density profiles of four member groups,
and found that they reach the surface density of field stars at about 10',
regardless of stellar mass.
The IMF of NGC 6231 is derived for the mass range 0.8 -- 45 Msun. The slope
of the IMF of NGC 6231 (Gamma = -1.1 +/- 0.1) is slightly shallower than the
canonical value, but the difference is marginal. In addition, the mass function
varies systematically, and is a strong function of radius - it is is very
shallow at the center, and very steep at the outer ring suggesting the cluster
is mass segregated. We confirm the mass segregation for the massive stars (m >~
8 Msun) by a minimum spanning tree analysis. Using a Monte Carlo method, we
estimate the total mass of NGC 6231 to be about 2.6 (+/- 0.6) x 10^3 Msun. We
constrain the age of NGC 6231 by comparison with evolutionary isochrones. The
age of the low-mass stars ranges from 1 to 7 Myr with a slight peak at 3 Myr.
However the age of the high mass stars depends on the adopted models and is 3.5
+/- 0.5 Myr from the non- or moderately-rotating models of Brott et al. as well
as the non-rotating models of Ekstr\"om et al. But the age is 4.0 -- 7.0 Myr if
the rotating models of Ekstr\"om et al. are adopted. This latter age is in
excellent agreement with the time scale of ejection of the high mass runaway
star HD 153919 from NGC 6231, albeit the younger age cannot be entirely
excluded.
Aims. A long timeline kinematic study of the archetypal CSO OQ 208 sheds
light on the physical properties of the most compact radio sources.
Methods. Archival data from the VLBA at 15 GHz over a time span of 13.6 yr
are used to investigate the kinematics of the radio source. The flux density
monitoring data obtained at the Michigan 26-meter radio telescope are also used
as supplementary information.
Results. At 8.4 and 15 GHz, the two lobes are resolved into two
sub-components, identified as hotspots. A knotty jet is linked with the NE
hotspot and traces back toward the geometric center. The core is too weak to be
detected. Significant flux density variation is found in the primary hotspots
with the maximum level of 62% (NE1) and 19% (SW1). The peak in the flux density
of NE1 leads that of SW1 by approximately 5.00 yr, suggesting that the
northeast lobe is advancing and the southwest lobe is receding. This light
travel difference indicates a radial distance difference between the two
hotspots of 1.53 pc, which indicates an inclination angle of about 80.8 degree
between the radio jet and the line of sight. The angular separation rate
between NE1 and SW1 is 0.027 mas/yr (or 0.133 c). The inner jet knot moves at
0.047 mas/yr (or 0.230 c), about 3.5 times the hotspot advancing speed.
Conclusions. The large viewing angle and the modest jet speed suggest a
mildly relativistic jet. The jet axis is close to the plane of the sky. The
separation rate and the distance between the two primary hotspots result in a
kinematic age of 255$\pm$17 yr, confirming that OQ 208 is indeed a young radio
source. In addition to the hotspot advancing motions, sideways motions provide
evidence that the lobes are obstructed by the external interstellar medium.
We present optical spectroscopy of a sample of 38 post-starburst quasars (PSQs) at z ~ 0.3, 29 of which have morphological classifications based on Hubble Space Telescope imaging. These broad-lined active galactic nuclei (AGNs) possess the spectral signatures of massive intermediate-aged stellar populations making them potentially useful for studying connections between nuclear activity and host galaxy evolution. We model the spectra in order to determine the ages and masses of the host stellar populations, and the black hole masses and Eddington fractions of the AGNs. Our model components include an instantaneous starburst, a power-law, and emission lines. We find the PSQs have MBH ~ 10^8 Msun accreting at a few percent of Eddington luminosity and host ~ 10^10.5 Msun stellar populations which are several hundred Myr to a few Gyr old. We investigate relationships among these derived properties, spectral properties, and morphologies. We find that PSQs hosted in spiral galaxies have significantly weaker AGN luminosities, older starburst ages, and narrow emission-line ratios diagnostic of ongoing star-formation when compared to their early-type counterparts. We conclude that the early-type PSQs are likely the result of major mergers and were likely luminous infrared galaxies in the past, while spiral PSQs with more complex star-formation histories are triggered by less dramatic events (e.g., harassment, bars). We provide diagnostics to distinguish the early-type and spiral hosts when high spatial resolution imaging is not available.
The empirical HOD model of Wang et al. 2006 fits, by construction, both the stellar mass function and correlation function of galaxies in the local Universe. In contrast, the semi-analytical models of De Lucia & Blazoit 2007 (DLB07) and Guo et al. 2011 (Guo11), built on the same dark matter halo merger trees than the empirical model, still have difficulties in reproducing these observational data simultaneously. We compare the relations between the stellar mass of galaxies and their host halo mass in the three models, and find that they are different. When the relations are rescaled to have the same median values and the same scatter as in Wang et al., the rescaled DLB07 model can fit both the measured galaxy stellar mass function and the correlation function measured in different galaxy stellar mass bins. In contrast, the rescaled Guo11 model still over-predicts the clustering of low-mass galaxies. This indicates that the detail of how galaxies populate the scatter in the stellar mass -- halo mass relation does play an important role in determining the correlation functions of galaxies. While the stellar mass of galaxies in the Wang et al. model depends only on halo mass and is randomly distributed within the scatter, galaxy stellar mass depends also on the halo formation time in semi-analytical models. At fixed value of infall mass, galaxies that lie above the median stellar mass -- halo mass relation reside in haloes that formed earlier, while galaxies that lie below the median relation reside in haloes that formed later. This effect is much stronger in Guo11 than in DLB07, which explains the over-clustering of low mass galaxies in Guo11. Our results illustrate that the assumption of random scatter in the relation between stellar and halo mass as employed by current HOD and abundance matching models may be problematic in case a significant assembly bias exists in the real Universe.
We present a detailed comparison of two approaches, the use of a pre-calculated database and simulated annealing (SA), for fitting the continuum spectral energy distribution (SED) of astrophysical objects whose appearance is dominated by surrounding dust. While pre-calculated databases are commonly used to model SED data, only few studies to date employed SA due to its unclear accuracy and convergence time for this specific problem. From a methodological point of view, different approaches lead to different fitting quality, demand on computational resources and calculation time. We compare the fitting quality and computational costs of these two approaches for the task of SED fitting to provide a guide to the practitioner to find a compromise between desired accuracy and available resources. To reduce uncertainties inherent to real datasets, we introduce a reference model resembling a typical circumstellar system with 10 free parameters. We derive the SED of the reference model with our code MC3D at 78 logarithmically distributed wavelengths in the range [0.3um, 1.3mm] and use this setup to simulate SEDs for the database and SA. Our result shows directly the applicability of SA in the field of SED modeling, since the algorithm regularly finds better solutions to the optimization problem than a pre-calculated database. As both methods have advantages and shortcomings, a hybrid approach is preferable. While the database provides an approximate fit and overall probability distributions for all parameters deduced using Bayesian analysis, SA can be used to improve upon the results returned by the model grid.
We study the far-infrared (IR) and sub-millimeter properties of a sample of ultraviolet (UV) selected galaxies at z\sim1.5. Using stacking at 250, 350 and 500 um from Herschel Space Observatory SPIRE imaging of the COSMOS field obtained within the HerMES key program, we derive the mean IR luminosity as a function of both UV luminosity and slope of the UV continuum beta. The IR to UV luminosity ratio is roughly constant over most of the UV luminosity range we explore. We also find that the IR to UV luminosity ratio is correlated with beta. We observe a correlation that underestimates the correlation derived from low-redshift starburst galaxies, but is in good agreement with the correlation derived from local normal star-forming galaxies. Using these results we reconstruct the IR luminosity function of our UV-selected sample. This luminosity function recovers the IR luminosity functions measured from IR selected samples at the faintest luminosities (Lir ~ 10^{11} L_sun), but might underestimate them at the bright-end (Lir > 5.10^{11} L_sun). For galaxies with 10^{11}<Lir/L_sun<10^{13}, the IR luminosity function of a UV selection recovers (given the differences in IR-based estimates) 52-65 to 89-112 per cent of the star-formation rate density derived from an IR selection. The cosmic star-formation rate density derived from this IR luminosity function is 61-76 to 100-133 per cent of the density derived from IR selections at the same epoch. Assuming the latest Herschel results and conservative stacking measurements, we use a toy model to fully reproduce the far IR luminosity function from our UV selection at z\sim 1.5. This suggests that a sample around 4 magnitudes deeper (i.e. reaching u \sim 30 mag) and a large dispersion of the IR to UV luminosity ratio are required.
Recent measurements of large-scale peculiar velocities from the cumulative kinematic Sunyaev-Zeldovich (KSZ) effect identified a bulk flow of galaxy clusters at $\sim 600-1,000$ km s$^{-1}$ on scales of $\sim0.5-1$ Gpc, roughly aligned with the all-sky Cosmic Microwave Background dipole. The signal originates from a residual dipole in the direction of galaxy clusters, at apertures containing zero monopole. Its amplitude increases with the X-ray luminosity of the clusters. The data need to be filtered to remove the primary CMB, thereby increasing the signal-to-noise ratio. Filtering cannot imprint a signal with the mentioned properties at cluster positions, but an inadequately designed and implemented filter can greatly suppress it. We show here that recent studies that failed to detect a large-scale flow indeed used inadequate implementations. These analysis assumed cluster extents and electron-pressure profiles inconsistent with the data. We show that the results from these alternative filters are consistent (although not identical) with our measurement, when filters are normalized to the data. The discrepancies can be traced to the assumptions on cluster profile and extent that reduce the efficiency of the filter and the possible existance of thermal Sunyaev-Zeldovich residual dipoles. The upcoming PLANCK maps, with their large frequency coverage, and in particular the 217GHz channel, will be important to probe the bulk flows as well as to remove spurious dipole signals and further identify the filtering schemes appropriate for this measurement.
Aiming at exploring the relationship between asteroids in cometary orbits and
other minor body populations from the observational point of view, I explore
the large photometric database of the Sloan Digital Sky Survey - Moving Objects
Catalog.
The sample of interest was carefully selected analyzing colors and orbital
properties within the data in the catalog. I computed the spectral slope for
each object and compared with published spectroscopic results of other
Asteroids in Cometary Orbits, as well as with other populations of asteroids in
the outer region of the Main belt and Trojans.
Using this extended database I find that Asteroids in Cometary Orbits with
Tisserand parameter below 2.9, and especially below 2.8, are most likely of
primitive origin. The population of objects with Tisserand parameter larger
than 2.9 is a mixture of populations ranging from the inner to the outer Main
belt.
Studying the trajectories of objects like stars, globular clusters or satellite galaxies in the Milky Way allows to trace the dark matter halo but requires reliable models of its gravitational potential. Realistic, yet simple and fully analytical models have already been presented in the past. However, improved as well as new observational constraints have become available in the meantime calling for a recalibration of the respective model parameters. Three widely used model potentials are revisited. By a simultaneous least-squared fit to the observed rotation curve, in-plane proper motion of Sgr A*, local mass/surface density and the velocity dispersion in Baade's window, parameters of the potentials are brought up-to-date. The mass at large radii - and thus in particular that of the dark matter halo - is hereby constrained by imposing that the most extreme halo blue horizontal-branch star known has to be bound to the Milky Way. The Galactic mass models are tuned to yield a very good match to recent observations. The mass of the dark matter halo is - within the limitations of the applied models - estimated in a fully consistent way. As a first application, the trajectory of the hypervelocity star HE 0437-5439 is re-investigated to check its suggested origin in the Large Magellanic Cloud (LMC). Despite their simplicity, the presented Milky Way mass models are well able to reproduce all observational constraints. Their analytical and simple form makes them ideally suited for fast and accurate orbit calculations. The LMC cannot be ruled out as HE 0437-5439's birthplace.
We explore the amplification of magnetic fields in the high-redshift Universe. For this purpose, we perform high-resolution cosmological simulations following the formation of primordial halos with \sim10^7 M_solar, revealing the presence of turbulent structures and complex morphologies at resolutions of at least 32 cells per Jeans length. Employing a turbulence subgrid-scale model, we quantify the amount of unresolved turbulence and show that the resulting turbulent viscosity has a significant impact on the gas morphology, suppressing the formation of low-mass clumps. We further demonstrate that such turbulence implies the efficient amplification of magnetic fields via the small-scale dynamo. We discuss the properties of the dynamo in the kinematic and non-linear regime, and explore the resulting magnetic field amplification during primordial star formation. We show that field strengths of \sim10^{-5} G can be expected at number densities of \sim5 cm^{-3}.
In this paper we consider the variability of the luminosity of a compact object (CO) powered by the accretion of an extremely inhomogeneous ("clumpy") stream of matter. The accretion of a single clump results in an X-ray flare: we adopt a simple model for the response of the CO to the accretion of a single clump, and derive a stochastic differential equation (SDE) for the accretion powered luminosity $L(t)$. We put the SDE in the equivalent form of an equation for the flares' luminosity distribution (FLD), and discuss its solution in the stationary case. As a case study, we apply our formalism to the analysis of the FLDs of Super-Giant Fast X-ray Transients (SFXTs), a peculiar sub-class of High Mass X-ray Binary Systems (HMXBs). We compare our theoretical FLDs to the distributions observed in the SFXTs IGR J16479-4514, IGR J17544-2619 and XTE J1739-302. Despite its simplicity, our model fairly agrees with the observed distributions, and allows to predict some properties of the stellar wind. Finally, we discuss how our model may explain the difference between the broad FLD of SFXTs and the much narrower distribution of persistent HMXBs.
In recent years, several potentially habitable, probably terrestrial exoplanets and exoplanet candidates have been discovered. The amount of CO2 in their atmosphere is of great importance for surface conditions and habitability. In the absence of detailed information on the geochemistry of the planet, this amount could be considered as a free parameter. Up to now, CO2 partial pressures for terrestrial planets have been obtained assuming an available volatile reservoir and outgassing scenarios. This study aims at calculating the allowed maximum CO2 pressure at the surface of terrestrial exoplanets orbiting near the outer boundary of the habitable zone by coupling the radiative effects of the CO2 and its condensation at the surface. These constraints might limit the permitted amount of atmospheric CO2, independent of the planetary reservoir. A 1D radiative-convective cloud-free atmospheric model was used. CO2 partial pressures are fixed according to surface temperature and vapor pressure curve. Considered scenarios cover a wide range of parameters. Results show that for planets in the habitable zone around K-, G-, and F-type stars the allowed CO2 pressure is limited by the vapor pressure curve and not by the planetary reservoir. The maximum CO2 pressure lies below the CO2 vapor pressure at the critical point of pcrit =73.8 bar. For M-type stars, CO2 pressures above pcrit are possible for almost all scenarios considered across the habitable zone. This implies that determining CO2 partial pressures for terrestrial planets by using only geological models is probably too simplified and might over-estimate atmospheric CO2 towards the outer edge of the habitable zone. (abridged)
The analysis of the spectral properties and dynamic evolution of a CME/shock event observed on November 1st 2003 in white-light by the LASCO coronagraph and in the ultraviolet by the UVCS instrument operating aboard SOHO, has been performed to compute the properties of some important plasma parameters in the middle corona below about 2 solar radii. Simultaneous observations obtained with the MLSO/Mk4 white-light coronagraph, providing both the early evolution of the CME expansion in the corona and the pre-shock electron density profile along the CME front, were also used to study this event. By combining the above information with the analysis of the metric type II radio emission detected by ground-based radio spectrographs, we finally derive estimates of the values of the local Alfv\'en speed and magnetic field strength in the solar corona.
According to satellite measurements the difference between polar and equatorial radius does not exceed 10 milliarcsec. These measurements are differential, and the absolute value of the solar diameter is not precisely known to a level of accuracy needed for finding variations during years or decades. Moreover the lifetime of a satellite is limited, and its calibration is not stable. This shows the need to continue ground-based observations of the Sun exploiting in particular the methods less affected by atmospheric turbulence, as the planetary transits and the total and annular eclipses. The state of art, the advantages and the limits of these two methods are here considered.
We lay out and apply methods to use proper motions of individual kinematic tracers for estimating the dynamical mass of star clusters. We first describe a simple projected mass estimator and then develop an approach that evaluates directly the likelihood of the discrete kinematic data given the model predictions. Those predictions may come from any dynamical modelling approach, and we implement an analytic King model, a spherical isotropic Jeans equation model and an axisymmetric, anisotropic Jeans equation model.We apply these approaches to the enigmatic globular cluster omega Centauri, combining the proper motion from van Leeuwen et al (2000) with improved photometric cluster membership probabilities. We show that all mass estimates based on spherical isotropic models yield $(4.55\pm 0.1) \times 10^6 M_{\odot} [D/5.5 \pm 0.2 kpc]^3$, where our modelling allows us to show how the statistical precision of this estimate improves as more proper motion data of lower signal-to-noise are included. MLM predictions, based on an anisotropic axisymmetric Jeans model, indicate for $\omega$ Cen that the inclusion of anisotropies is not important for the mass estimates, but that accounting for the flattening is: flattened models imply $(4.05\pm 0.1) \times 10^6 M_{\odot} [D/5.5 \pm 0.2 kpc]^3$, 10% lower than when restricting the analysis to a spherical model. The best current distance estimates imply an additional uncertainty in the mass estimate of 12%.
An accretion scenario in which the material captured by a black hole from its environment is assumed to be magnetized (\beta ~ 1) is discussed. We show that the accretion picture in this case is strongly affected by the magnetic field of the flow itself. The accretion power within this Magnetically Controlled Accretion (MCA) scenario is converted predominantly into the magnetic energy of the accretion flow. The rapidly amplified field prevents the accretion flow from forming a homogeneous Keplerian disk. Instead, the flow is decelerated by its own magnetic field at a large distance (Shvartsman radius) from the black hole and switches into a non-Keplerian dense magnetized slab. The material in the slab is confined by the magnetic field and moves towards the black hole on the time scale of the magnetic field annihilation. The basic parameters of the slab are evaluated. Interchange instabilities in the slab may lead to a formation of Z-pinch type configuration of the magnetic field over the slab in which the accretion power can be converted into jets and high-energy radiation.
As an entry for the 2012 Gordon-Bell performance prize, we report performance results of astrophysical N-body simulations of one trillion particles performed on the full system of K computer. This is the first gravitational trillion-body simulation in the world. We describe the scientific motivation, the numerical algorithm, the parallelization strategy, and the performance analysis. Unlike many previous Gordon-Bell prize winners that used the tree algorithm for astrophysical N-body simulations, we used the hybrid TreePM method, for similar level of accuracy in which the short-range force is calculated by the tree algorithm, and the long-range force is solved by the particle-mesh algorithm. We developed a highly-tuned gravity kernel for short-range forces, and a novel communication algorithm for long-range forces. The average performance on 24576 and 82944 nodes of K computer are 1.53 and 4.45 Pflops, which correspond to 49% and 42% of the peak speed.
We suggest a specific new class of low-frequency g-modes in superfluid neutron stars. We determine the Brunt-Vaisala frequency for these modes and demonstrate that they can be unstable with respect to convection. The criterion for the instability onset (analogue of the well known Schwarzschild criterion) is derived. It is very sensitive to equation of state and a model of nucleon superfluidity. In particular, convection may occur for both positive and negative temperature gradients. Our results have interesting implications for neutron star cooling and seismology.
We present a multi-wavelength study of the gravitational lens COSMOS
J095930+023427 (z=0.89), together with the associated galaxy group located at
$z\sim0.7$ along the line of sight and the lensed background galaxy.
The source redshift is currently unknown, but estimated to be at $z_s \sim
2$. The analysis is based on the available public HST, Subaru, Chandra imaging
data, and VLT spectroscopy. The lensing system is an early-type galaxy showing
a strong [OII] emission line, and produces 4 bright images of the distant
background source. It has an Einstein radius of 0.79", about 4 times large than
the effective radius. We perform a lensing analysis using both a Singular
Isothermal Ellipsoid (SIE) and a Peudo-Isothermal Elliptical Mass Distribution
(PIEMD) for the lensing galaxy, and find that the final results on the total
mass, the dark matter (DM) fraction within the Einstein radius and the external
shear due to a foreground galaxy group are robust with respect of the choice of
the parametric model and the source redshift (yet unknown). We measure the
luminous mass from the photometric data, and find the DM fraction within the
Einstein radius $f_{\rm DM}$ to be between $0.71\pm 0.13$ and $0.79 \pm 0.15$,
depending on the unknown source redshift. Meanwhile, the non-null external
shear found in our lensing models supports the presence and structure of a
galaxy group at $z\sim0.7$, and an independent measurement of the 0.5-2 keV
X-ray luminosity within 20" around the X-ray centroid provides a group mass of
$M=(3-10)\times 10^{13}$ M$_{\odot}$, in good agreement with the previous
estimate derived through weak lensing analysis.
We present the cosmological analysis of 752 photometrically-classified Type Ia Supernovae (SNe Ia) obtained from the full Sloan Digital Sky Survey II (SDSS-II) Supernova (SN) Survey, supplemented with host-galaxy spectroscopy from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). Our photometric-classification method is based on the SN typing technique of Sako et al. (2011), aided by host galaxy redshifts (0.05<z<0.55). SNANA simulations of our methodology estimate that we have a SN Ia typing efficiency of 70.8%, with only 3.9% contamination from core-collapse (non-Ia) SNe. We demonstrate that this level of contamination has no effect on our cosmological constraints. We quantify and correct for our selection effects (e.g., Malmquist bias) using simulations. When fitting to a flat LambdaCDM cosmological model, we find that our photometric sample alone gives omega_m=0.24+0.07-0.05 (statistical errors only). If we relax the constraint on flatness, then our sample provides competitive joint statistical constraints on omega_m and omega_lambda, comparable to those derived from the spectroscopically-confirmed three-year Supernova Legacy Survey (SNLS3). Using only our data, the statistics-only result favors an accelerating universe at 99.96% confidence. Assuming a constant wCDM cosmological model, and combining with H0, CMB and LRG data, we obtain w=-0.96+0.10-0.10, omega_m=0.29+0.02-0.02 and omega_k=0.00+0.03-0.02 (statistical errors only), which is competitive with similar spectroscopically confirmed SNe Ia analyses. Overall this comparison is re-assuring, considering the lower redshift leverage of the SDSS-II SN sample (z<0.55) and the lack of spectroscopic confirmation used herein. These results demonstrate the potential of photometrically-classified SNe Ia samples in improving cosmological constraints.
We present a census of the disk population for UKIDSS selected brown dwarfs in the 5-10 Myr old Upper Scorpius OB association. For 116 objects originally identified in UKIDSS, the majority of them not studied in previous publications, we obtain photometry from the WISE database. The resulting colour-magnitude and colour-colour plots clearly show two separate populations of objects, interpreted as brown dwarfs with disks (class II) and without disks (class III). We identify 27 class II brown dwarfs, 14 of them not previously known. This fraction among brown dwarfs was found to be similar to results for K/M stars in Upper Scorpius, suggesting that the lifetimes of disks are independent of the mass of the central object for low-mass stars and brown dwarfs. 5 out of 27 disks (19%) lack excess at 3.4 and 4.6 microns and are potential transition disks (i.e. are in transition from class II to class III). The transition disk fraction is comparable to low-mass stars. We estimate that the timescale for a typical transition from class II to class III is less than 0.4 Myr for brown dwarfs. These results suggest that the evolution of brown dwarf disks mirrors the behaviour of disks around low-mass stars, with disk lifetimes on the order of 5-10 Myr and a disk clearing timescale significantly shorter than 1 Myr.
Recently, a number of new galaxy clusters have been detected by the ESA-Planck satellite, the South Pole Telescope and the Atacama Cosmology Telescope using the Sunyaev-Zeldovich effect. Several of the newly detected clusters are massive, merging systems with disturbed morphology in the X-ray surface brightness. Diffuse radio sources in clusters, called giant radio halos and relics, are direct probes of cosmic rays and magnetic fields in the intra-cluster medium. These radio sources are found to occur mainly in massive merging clusters. Thus, the new SZ-discovered clusters are good candidates to search for new radio halos and relics. We have initiated radio observations of the clusters detected by Planck with the Giant Metrewave Radio Telescope. These observations have already led to the detection of a radio halo in PLCKG171.9-40.7, the first giant halo discovered in one of the new Planck clusters.
Aims. A model of heliosheath density and energy spectra of alpha-particles and He+ ions carried by the solar wind is developed. Neutralization of heliosheath He+ ions, mainly by charge exchange (CX) with neutral interstellar H and He atoms, gives rise to ~0.2 - ~100 keV fluxes of energetic neutral He atoms (He ENA). Such fluxes, if observed, would give information about plasmas in the heliosheath and heliospheric tail. Methods. Helium ions crossing the termination shock (TS) constitute suprathermal (test) particles convected by (locally also diffusing through) hydrodynamically calculated background plasma flows (three versions of flows are employed). The He ions proceed from the TS towards heliopause (HP) and finally to the heliospheric tail (HT). Calculations of the evolution of alpha- and He+ particle densities and energy spectra include binary interactions with background plasma and interstellar atoms, adiabatic heating (cooling) resulting from flow compression (rarefaction), and Coulomb scattering on background plasma. Results. Neutralization of suprathermal He ions leads to the emergence of He ENA fluxes with energy spectra modified by the Compton-Getting effect at emission and ENA loss during flight to the Sun. Energy-integrated He ENA intensities are in the range ~0.05 - ~50 cm^-2 s^-1 sr^-1 depending on spectra at the TS (assumed kappa-distributions), background plasma model, and look direction. The tail/apex intensity ratio varies between ~1.8 and ~800 depending on model assumptions. Energy spectra are broad with maxima in the ~0.2 - ~3 keV range depending on the look direction and model. Conclusions. Expected heliosheath He ENA fluxes may be measurable based on the capabilities of the IBEX spacecraft. Data could offer insight into the heliosheath structure and improve understanding of the post-TS solar wind plasmas. HT direction and extent could be assessed.
We present the final release of the multi-wavelength XMM-LSS data set,covering the full survey area of 11.1 square degrees, with X-ray data processed with the latest XMM-LSS pipeline version. The present publication supersedes the Pierre et al.(2007) catalogue pertaining to the initial 5 square degrees. We provide X-ray source lists in the customary energy bands (0.5-2 and 2-10 keV) for a total of 6721 objects in the deep full-exposure catalogue and 5572 in the 10ks-limited one, above a detection likelihood of 15 in at least one band. We also provide a multiwavelength catalogue, cross-correlating our list with IR, NIR, optical and UV catalogues. Customary data products (X-ray FITS images, CFHTLS and SWIRE thumbnail images) are made available together with our interactively queriable database in Milan, while a static snapshot of the catalogues will be supplied to CDS, as soon as final acceptance is completed.
As part of the "Dust, Ice, and Gas In Time (DIGIT)" Herschel Open Time Key Program, we present Herschel photometry (at 70, 160, 250, 350 and 500 micron) of 31 Weak-Line T Tauri star (WTTS) candidates in order to investigate the evolutionary status of their circumstellar disks. Thirteen stars in our sample had circumstellar disks previously known from infrared observations at shorter wavelengths, while eighteen of them had no previous evidence for a disk. We detect a total of 15 disks as all previously known disks are detected at one or more Herschel wavelengths and two additional disks are identified for the first time. The spectral energy distributions (SEDs) of our targets seem to trace the dissipation of the primordial disk and the transition to the debris disk regime. Seven of the 15 disks appear to be optically thick primordial disks, including two objects with SEDs indistinguishable from those of typical Classical T Tauri stars, four objects that have significant deficit of excess emission at all IR wavelengths, and one "pre-transitional" object with a known gap in the disk. Despite their previous WTTS classification, we find that the seven targets in our sample with optically thick disks show evidence for accretion. The remaining eight disks have weaker IR excesses similar to those of optically thin debris disks. Six of them are warm and show significant 24 micron Spitzer excesses, while the last two are newly identified cold debris-like disks with photospheric 24 micron fluxes, but significant excess emission at longer wavelengths. The Herschel photometry also places strong constraints on the non-detections, where systems with F70/F70,star > 5 - 15 and L,disk/L,star > 1xE-3 to 1xE-4 can be ruled out. We present preliminary models for both the optically thick and optically thin disks and discuss our results in the context of the evolution and dissipation of circumstellar disks.
The class of tidal features around galaxies known variously as "shells" or "umbrellas" comprises debris that has arisen from high-mass-ratio mergers with low impact parameter; the nearly radial orbits of the debris give rise to a unique morphology, a universal density profile, and a tight correlation between positions and velocities of the material. As such they are accessible to analytical treatment, and can provide a relatively clean system for probing the gravitational potential of the host galaxy. In this work we present a simple analytical model that describes the density profile, phase-space distribution, and geometry of a shell, and whose parameters are directly related to physical characteristics of the interacting galaxies. The model makes three assumptions: that their orbit is radial, that the potential of the host is spherical at the shell radii, and that the satellite galaxy had a Maxwellian velocity distribution. We quantify the error introduced by the first two assumptions and show that selecting shells by their appearance on the sky is a sufficient basis to assume that these simplifications are valid. We further demonstrate that (1) given only an image of a shell, the radial gravitational force at the shell edge and the phase-space density of the satellite are jointly constrained, (2) that combining the image with measurements of either point line-of-sight velocities or integrated spectra will yield an independent estimate of the gravitational force at a shell, and (3) that an independent measurement of this force is obtained for each shell observed around a given galaxy, potentially enabling a determination of the galactic mass distribution.
This paper presents the Suzaku results obtained for the Sagittarius (Sgr) C region using the concept of X-ray reflection nebulae (XRNe) as the echo of past flares from the super massive black hole, Sgr A*. The Sgr C complex is composed of several molecular clouds proximately located in projected distance. The X-ray spectra of Sgr C were analyzed on the basis of a view that XRNe are located inside the Galactic center plasma X-ray emission with an oval distribution around Sgr A*. We found that the XRNe are largely separated in the line-of-sight position, and are associated with molecular clouds in different velocity ranges detected by radio observations. We also applied the same analysis to the Sgr B XRNe and completed a long-term light curve for Sgr A* occurring in the past. As a new finding, we determined that Sgr A* was experiencing periods of high luminosity already 500 years ago, which is longer than the previously reported value. Our results are consistent with a scenario that Sgr A* was continuously active with sporadic flux variabilities of Lx = 1-3 x 10^39 erg s^-1 in the past 50 to 500 years. The average past luminosity was approximately 4-6 orders of magnitude higher than that presently observed. In addition, two short-term flares of 5-10 years are found. Thus, the past X-ray flare should not be a single short-term flare, but can be interpreted as multiple flares superposed on a long-term high state.
We have studied the variability of PSR J0529-6652, a radio pulsar in the LMC, using observations conducted at 1390 MHz with the Parkes 64-m telescope. PSR J0529-6652 is detectable as a single pulse emitter, with amplitudes that classify the pulses as giant pulses. This makes PSR J0529-6652 the second known giant pulse emitter in the LMC, after PSR B0540-69. The fraction of the emitted pulses detectable from PSR J0529-6652 at this frequency is roughly two orders of magnitude greater than it is for either PSR B0540-69 or the Crab pulsar (if the latter were located in the LMC). We have measured a pulse nulling fraction of 83.3 \pm 1.5% and an intrinsic modulation index of 4.07 \pm 0.29 for PSR J0529-6652. The modulation index is significantly larger than values previously measured for typical radio pulsars but is comparable to values reported for members of several other neutron star classes. The large modulation index, giant pulses, and large nulling fraction suggest that this pulsar is phenomenologically more similar to these other, more variable sources, despite having spin and physical characteristics that are typical of the unrecycled radio pulsar population. The large modulation index also does not appear to be consistent with the small value predicted for this pulsar by a model of polar cap emission outlined by Gil & Sendyk (2000). This conclusion depends to some extent on the assumption that PSR J0529-6652 is exhibiting core emission, as suggested by its simple profile morphology, narrow profile width, and previously measured profile polarization characteristics.
We analyze the distribution of extrasolar planets (both confirmed and Kepler
candidates) according to their orbital periods P and planetary radii R. Among
confirmed planets, we find compelling evidence for a paucity of bodies with 3 <
R < 10 R_\oplus, where R_\oplus in the Earth's radius, and P < 2-3 days. We
have christened this region a "sub-Jovian Pampas". The same trend is detected
in multiplanet Kepler candidates. Although approximately 16 Kepler
single-planet candidates inhabit this Pampas, at least 7 are probable false
positives (FP). This last number could be significantly higher if the ratio of
FP is higher than 10%, as suggested by recent studies.
In a second part of the paper we analyze the distribution of planets in the
(P,R) plane according to stellar metallicities. We find two interesting trends:
(i) a lack of small planets (R < 4 R_\oplus) with orbital periods P < 5 days in
metal-poor stars, and (ii) a paucity of sub-Jovian planets (4 R_\oplus < R < 8
R_\oplus) with P < 100 days, also around metal-poor stars. Although all these
trends are preliminary, they appear statistically significant and deserve
further scrutiny. If confirmed, they could represent important constraints on
theories of planetary formation and dynamical evolution.
Bruno Rossi is considered one of the fathers of modern physics, being also a pioneer in virtually every aspect of what is today called high-energy astrophysics. At the beginning of 1930s he was the pioneer of cosmic ray research in Italy, and, as one of the leading actors in the study of the nature and behavior of the cosmic radiation, he witnessed the birth of particle physics and was one of the main investigators in this fields for many years. While cosmic ray physics moved more and more towards astrophysics, Rossi continued to be one of the inspirers of this line of research. When outer space became a reality, he did not hesitate to leap into this new scientific dimension. Rossi's intuition on the importance of exploiting new technological windows to look at the universe with new eyes, is a fundamental key to understand the profound unity which guided his scientific research path up to its culminating moments at the beginning of 1960s, when his group at MIT performed the first {\it in situ} measurements of the density, speed and direction of the solar wind at the boundary of Earth's magnetosphere, and when he promoted the search for extra-solar sources of X rays. A visionary idea which eventually led to the breakthrough experiment which discovered Scorpius X-1 in 1962, and inaugurated X-ray astronomy.
The spatially flat and isotropic cosmological model of Brans-Dicke theory with coupling parameter $\omega\neq-3/2$ is quantized by the approach of loop quantum cosmology. An interesting feature of this model is that, although the Brans-Dicke scalar field is non-minimally coupled with curvature, it can still play the role of an emergent time variable. In the quantum theory, the classical differential equation which represents cosmological evolution is replaced by a quantum difference equation. The effective Hamiltonian and modified dynamical equations of loop quantum Brans-Dicke cosmology are also obtained, which lay a foundation for the phenomenological investigation to possible quantum gravity effects in cosmology. The effective equations indicate that the classical big bang singularity is again replaced by a quantum bounce in loop quantum Brans-Dicke cosmology.
The properties of the quark and hadron Universe are explored. Kinetic theory considerations are presented proving that hadron abundances after phase transformation from quarks to hadrons remain intact till abundances of hadrons become irrelevant. The hadronization process and the evolution of hadron yields is described in detail.
We use a dynamical systems analysis to investigate the future behaviour of Einstein-Aether cosmological models with a scalar field coupling to the expansion of the aether and a non-interacting perfect fluid. The stability of the equilibrium solutions are analysed and the results are compared with the standard inflationary cosmological solutions and previously studied cosmological Einstein-Aether models.
A model of a cloud formed by massive strings is used as a source of Bianchi type II. We assumed that the expansion $(\theta)$ in the model is proportional to the shear $(\sigma)$. To get exact solution, we have considered the equation of state of the fluid to be in the stiff form. It is found that the bulk viscosity plays a very important rule in the history of the universe. In presence of bulk viscosity the particles dominate over strings whereas in absence of it, strings dominate over the particles which is not in consistence with the recent observations. Also we observe that the viscosity caused the expansion of the universe to be accelerating. Our models are evolving from an early decelerating phase to a late time accelerating phase. The physical and geometrical behavior of these models are discussed.
We consider the baryon-to-dark matter ratio in models where the dark matter and baryon densities depend on angular fields \theta_{d} and \theta_{b} according to \rho_{d} ~ \theta_{d}^{\alpha} and \rho_{b} ~ \theta_{b}^{\beta}, with all values of \theta_{d} and \theta_{b} being equally probable in a given randomly-selected domain. Under the assumption that anthropic selection depends primarily on the baryon density in galaxies at spherical collapse, we show that the probability density function for the baryon-to-dark matter ratio r = \Omega_{B}/\Omega_{DM} is purely statistical in nature and is independent of anthropic selection. We compute the probability density function for r as a function of \alpha and \beta and show that the observed value of the baryon-to-dark matter ratio, r \approx 1/5, is natural in this framework.
High-pressure xenon gas is an attractive detection medium for a variety of applications in fundamental and applied physics. In this paper we study the transport properties of ionization electrons, and the mechanism of electron-ion recombination, in xenon gas at 10 bar pressure. For this purpose, we use a source of alpha particles in the NEXT-DEMO time projection chamber, the large scale prototype of the NEXT-100 neutrinoless double beta decay experiment, in three different drift electric field configurations. Our electron drift velocity and longitudinal diffusion results are similar to expectations based on available electron scattering cross sections on pure xenon, favoring low-diffusion models. In addition, two types of measurements addressing the connection between the ionization and scintillation yields were performed. On the one hand we observe, for the first time in xenon gas, large event-by-event correlated fluctuations between the ionization and scintillation signals, similarly to what has already been observed in liquid xenon. On the other hand, we study the field dependence of the average scintillation yield. Both types of measurements may shed light on the mechanism of electron-ion recombination in xenon gas for highly-ionizing particles.
We provide a precise and quantitative holographic description of a class of inflationary slow-roll models. The dual QFT is a deformation of a three-dimensional CFT by a nearly marginal operator, which, in the models we consider, generates an RG flow to a nearby IR fixed point. These models describe hilltop inflation, where the inflaton rolls from a local maximum of the potential in the infinite past (corresponding to the IR fixed point of the dual QFT) to reach a nearby local minimum in the infinite future (corresponding to the UV of the dual QFT). Through purely holographic means, we compute the spectra and bispectra of scalar and tensor cosmological perturbations. The QFT correlators to which these observables map holographically may be calculated using conformal perturbation theory, even when the dual QFT is strongly coupled. Both the spectra and the bispectra may be expressed this way in terms of CFT correlators that are fixed, up to a few constants, by conformal invariance. The form of slow-roll inflationary correlators is thus determined by the perturbative breaking of the de Sitter isometries away from the fixed point. Setting the constants to their values obtained by AdS/CFT at the fixed point, we find exact agreement with known expressions for the slow-roll power spectra and non-Gaussianities.
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We investigated the development of astronomy and astrophysics research productivity in Turkey in terms of publication output and their impacts as reflected in the Science Citation Index (SCI) for the period 1980-2010. It includes 838 refereed publications, including 801 articles, 16 letters, 15 reviews, and six research notes. The number of papers were prominently increased after 2000 and the average number of papers per researcher is calculated as 0.89. Total number of received citations for 838 papers is 6938, while number of citations per papers is approximately 8.3 in 30 years. Publication performance of Turkish astronomers and astrophysicists was compared with those of seven countries that have similar gross domestic expenditures on research and development, and members of Organization for Economic Co-operation and Development (OECD). Our study reveals that the output of astronomy and astrophysics research in Turkey has gradually increased over the years.
We present the Photon-Plasma code, a modern high order charge conserving particle-in-cell code used for simulating relativistic plasmas. The code is using a high order implicit field solver and a novel high order charge conserving interpolation scheme for particle-to-cell interpolation and charge deposition. It includes powerful diagnostics tools with on-the-fly particle tracking, synthetic spectra integration, and 2D volume slicing, and a new method to correctly account for radiative cooling in the simulations. A robust technique for (time-dependent) particle and field fluxes on the boundaries is also presented. Using a hybrid OpenMP and MPI approach the code scales efficiently from 8 to more than 250.000 cores with almost linear scale up on a range of architectures. The code is tested with the classical benchmarks particle heating, cold beam instability, and two-stream instability. We also present particle-in-cell simulations of the Kelvin-Helmholtz instability, and new results on radiative collisionless shocks.
We present optical and near-IR spectroscopic observations of the luminous blue variable SN 2009ip during its remarkable photometric evolution of 2012. The spectra sample three key points in the SN 2009ip lightcurve, corresponding to its initial brightening in August (2012-A) and its dramatic rebrightening in early October (2012-B). Based on line fluxes and velocities measured in our spectra, we find a surprisingly low I(H-alpha)/I(H-beta) ratio (~1.5) in the 2012-B spectra. Such a ratio implies either a rare Case B recombination scenario where H-alpha, but not H-beta, is optically thick, or an extremely high density for the circumstellar material of n_e > 10^(13) cm^(-3). The H-alpha line intensity yields a minimum radiating surface area of >~20,000 AU^2 in H-alpha at the peak of SN 2009ip's photometric evolution. Combined with the nature of this object's spectral evolution in 2012, a high circumstellar density and large radiating surface area imply the presence of a thin disk geometry around the central star (and, consequently, a possible binary companion), suggesting that the observed 2012-B rebrightening of SN 2009ip can be attributed to the illumination of the disk's inner rim by fast-moving ejecta produced by the underlying events of 2012-A.
We study the effect of H I ionizing photons escaping from the high-z galaxies on the He II ionizing ultraviolet background (UVB) radiation. We show, while these photons do not directly interact with He II ions, they play an important role through radiative transport in modifying the shape of He II ionizing part of UVB spectrum. Within the observed range of UV escape from galaxies, we show the rapid increase in He II Lyman alpha effective optical depth at z ~ 2.7 can be naturally explained without resorting to pre-overlap era of He II reionization. Therefore, a well measured He II Lyman alpha effective optical depth vs z relationship can be used to constrain the redshift evolution of UV escape from high-z galaxies. Our study also stresses the importance of including galaxy contribution even in the fluctuating UV background calculations.
Recent findings hint that the winds of massive stars with poorer metallicity
than the SMC may be stronger than predicted by theory. Besides calling the
paradigm of radiation driven winds into question, this result would impact the
predicted evolutionary paths of massive stars, their calculated ionizing
radiation and mechanical feedback and the role these objects play at different
stages of the Universe. The field needs a systematic study of the winds of a
large set of very metal poor massive stars, but the sampling of spectral types
is particularly poor in the very early types. This paper's goal is to increase
the list of known O-type stars in the dwarf irregular galaxy IC1613, whose
metallicity is smaller than the SMC's by roughly a factor 2.
Using the reddening-free Q-parameter, evolutionary masses and GALEX
photometry, we built a list of very likely O-type stars. We obtained
low-resolution R~1000 GTC-OSIRIS spectra for a fraction of them and performed
spectral classification, the only way to unequivocally confirm candidate
OB-stars. We have discovered 8 new O-type stars in IC1613, increasing the list
of 7 known O-type stars in this galaxy by a factor of 2. The best quality
spectra were analyzed with the model atmosphere code FASTWIND to derive stellar
parameters. We present the first spectral type -- effective temperature scale
for O-stars beyond the SMC. The derived effective temperature calibration for
IC1613 is about 1000K hotter than the scale at the SMC. The analysis of an
increased list of O-type stars will be crucial for the studies of the winds and
feedback of massive stars at all ages of the Universe.
The Milky Way (MW) dwarf system presents two exceptional features, namely it forms a thick plane called the Vast Polar Structure (VPOS), and the two biggest dwarves, the Magellanic Clouds (MCs), are irregular galaxies that are almost never seen at such a proximity from a luminous, L* galaxy. Investigating from our modelling of M31 as a result of a former gas-rich major merger, we find that one of the expected tidal tail produced during the event may have reached the MW. Such a coincidence may appear quite exceptional, but the MW indeed lies within the small volume delineated by the tidal tail at the present epoch. In our scenario, most of the MW dwarves, including the MCs, may have been formed within a tidal tail formed during the former merger in the Local Group. It leads to a fair reproduction of the VPOS as well as to a simple explanation of the MCs proximity to the MW, i.e. accounting for both exceptional features of the MW dwarf distributions. However this scenario predicts dark-matter free MW dwarves, which is in apparent contradiction with their intrinsically large velocity dispersions. To be established or discarded, this requires to further investigate their detailed interactions with the MW potential.
We show that a White Dwarf-White Dwarf (WD-WD) binary with semi-major axis a=1-300 AU, which is orbited by a stellar mass outer perturber with a moderate pericenter r_{p, out} \sim 3-10 x a, has a few percent chance of experiencing a head-on collision within ~5 Gyr. Such a perturber is sufficiently distant to allow the triple system to remain intact for millions of orbits while efficiently exchanging angular momentum with the WD-WD binary. In ~ 5% of the initial orientations, the inner orbit efficiently scans the (equal energy) phase space in the region of zero angular momentum. In these systems, the binary experiences increasingly closer, stochastic, pericenter approaches r_p a/2N with the increasing number (N) of orbits elapsed. Within N~10^5(a/30AU) orbits, a collision is likely to occur. This is shown by performing \simten thousand 3-body integrations and is explained by simple analytic arguments. The collisions are conservatively restricted to "clean" collisions in which all passages prior to the collision are greater than 4R_WD=4x10^9cm. In particular, within the last single orbit, the pericenter changes from r_p>4R_WD to a collision value of r_p<2R_WD. The effects of tidal deformations and General Relativistic (GR) corrections are negligible in these scenarios. The WDs approach each other with a high velocity >3000 km/s and the collision is likely to detonate the WDs leading to a type Ia SNe. If a significant fraction of WDs reside in such triples, the rate of such collisions is as high as the SNe Ia rate, and it is possible that some or all type Ia SNe occur in this way. Such SNe have a unique gravitational wave signature, which will allow a decisive identification in the future.
We present precise HI 21 cm absorption line redshifts observed in multiple epochs to directly constrain the secular redshift drift dz/dt_o or the cosmic acceleration, dv/dt_o. A comparison of literature analog spectra to contemporary digital spectra shows significant acceleration likely attributable to systematic instrumental errors. However, we obtain robust constraints using primarily Green Bank Telescope digital data. Ten objects spanning z=0.09-0.69 observed over 13.5 years show dz/dt_o = (-2.3 +/- 0.8) x 10^-8 yr^-1 or dv/dt_o = -5.5 +/- 2.2 m/s/yr. The best constraint from a single object, 3C286 at <z> = 0.692153275(85), is dz/dt_o = (1.6 +/- 4.7) x 10^-8 yr^-1 or dv/dt_o =2.8 +/- 8.4 m/s/yr. These measurements are three orders of magnitude larger than the theoretically expected acceleration at z=0.5, dz/dt_o = 2 x 10^-11 yr^-1 or dv/dt_o = 0.3 cm/s/yr, but they demonstrate the lack of peculiar acceleration in absorption line systems and the long-term frequency stability of modern radio telescopes. A comparison of UV metal absorption lines to the 21 cm line improves constraints on the cosmic variation of physical constants: Delta(alpha^2 g_p mu)/(alpha^2 g_p mu) = (-1.2 +/- 1.4) x 10^-6 in the redshift range z=0.24-2.04. The linear evolution over the last 10.4 Gyr is (-0.2 +/- 2.7) x 10^-16 yr^-1, consistent with no variation. The cosmic acceleration could be directly measured in ~125 years using current telescopes or in ~5 years using a Square Kilometer Array, but systematic effects will arise at the 1 cm/s/yr level.
Recent observations of massive galaxies indicate that they double in mass and quintuple in size between redshift z = 1 and the present, despite undergoing very little star formation, suggesting that galaxy mergers drive the evolution. Since these galaxies will contain supermassive black holes, this suggests a larger black hole merger rate, and therefore a larger gravitational-wave signal, than previously expected. We calculate the merger-driven evolution of the mass function, and find that merger rates are 10 to 30 times higher and gravitational waves are 3 to 5 times stronger than previously estimated, so that the gravitational-wave signal may already be detectable with existing data from pulsar timing arrays. We also provide an explanation for the disagreement with past estimates that were based on dark matter halo simulations.
We present abundances for seven stars in the (extremely) low-metallicity tail of the Sculptor dwarf spheroidal galaxy, from spectra taken with X-shooter on the ESO VLT. Targets were selected from the Ca II triplet (CaT) survey of the Dwarf Abundances and Radial Velocities Team (DART) using the latest calibration. Of the seven extremely metal-poor candidates, five stars are confirmed to be extremely metal-poor (i.e., [Fe/H]<-3 dex), with [Fe/H]=-3.47 +/- 0.07 for our most metal-poor star. All are around or below [Fe/H]=-2.5 dex from the measurement of individual Fe lines. These values are in agreement with the CaT predictions to within error bars. None of the seven stars is found to be carbon-rich. We estimate a 2-13% possibility of this being a pure chance effect, which could indicate a lower fraction of carbon-rich extremely metal-poor stars in Sculptor compared to the Milky Way halo. The [alpha/Fe] ratios show a range from +0.5 to -0.5, a larger variation than seen in Galactic samples although typically consistent within 1-2sigma. One star seems mildly iron-enhanced. Our program stars show no deviations from the Galactic abundance trends in chromium and the heavy elements barium and strontium. Sodium abundances are, however, below the Galactic values for several stars. Overall, we conclude that the CaT lines are a successful metallicity indicator down to the extremely metal-poor regime and that the extremely metal-poor stars in the Sculptor dwarf galaxy are chemically more similar to their Milky Way halo equivalents than the more metal-rich population of stars.
We consider the orbital evolution of the S-stars, the young main-sequence stars near the supermassive black hole (SBH) at the Galactic center (GC), and put constraints on competing models for their origin. Our analysis includes for the first time the joint effects of Newtonian and relativistic perturbations to the motion, including the dragging of inertial frames by a spinning SBH as well as torques due to finite-N asymmetries in the field-star distribution (resonant relaxation, RR). The evolution of the S-star orbits is strongly influenced by the Schwarzschild barrier (SB), the locus in the (E,L) plane where RR is ineffective at driving orbits to higher eccentricities. Formation models that invoke tidal disruption of binary stars by the SBH tend to place stars below (i.e., at higher eccentricities than) the SB; some stars remain below the barrier, but most stars are able to penetrate it, after which they are subject to RR and achieve a nearly thermal distribution of eccentricities. This process requires roughly 50 Myr in nuclear models with relaxed stellar cusps, or >~10 Myr, regardless of the initial distribution of eccentricities, in nuclear models that include a dense cluster of 10 M_Sun black holes. We find a probability of <~1% for any S-star to be tidally disrupted by the SBH over its lifetime.
It has been suggested that an intermediate-massive black hole (IMBH) with mass 10^{3-5} M_\odot could fall into the galactic center (GC) and form an massive black hole binary (MBHB) with the central supermassive black hole, but current observational are not sensitive to constrain all mass and distance ranges. Motivated by the recent discovery that MBHBs could enhance the rate of tidal-disruption events (TDEs) of stellar objects, we investigate the prospect of using stellar-disruption rate to probe IMBHs in the GC. We incorporated the perturbation by an IMBH into the loss-cone theory and calculated the stellar-disruption rates in the GC. We found that an IMBH heavier than 2000 M_\odot could distinguishably enhance the stellar-disruption rate. By comparing observations of Sgr A* with the fall-back model for stellar debris, we suggested that the TDE rate in our Galaxy should not significantly exceed 0.002 per year, therefore a fraction of the parameter space for the IMBH, concentrating at the high-mass end, can already be excluded. To derive constraint in the remaining parameter space, it is crucial to observationally confirm or reject the stellar-disruption rate between 10^{-4} and 0.01 yr^{-1}, and we discussed possible strategies to make such measurements.
An extremely large void and a cosmic texture are two possible explanations for the cold spot seen in the cosmic microwave background (CMB). We investigate how well these two hypotheses can be tested with weak lensing of 21-cm fluctuations from the epoch of reionization (EoR) measured with the Square Kilometer Array (SKA). While the void explanation for the cold spot can be tested with SKA, given enough observation time, the texture scenario requires significantly prolonged observations, at the highest frequencies that correspond to the EoR, over the field of view containing the cold spot.
SBW1 is a B supergiant surrounded by a ring nebula that is a nearby twin of SN 1987A. We present images and spectra of SBW1 obtained with HST, Spitzer, and Gemini South. HST images of SBW1 do not exhibit long Rayleigh-Taylor fingers, which are presumed to cause the hotspots in the SN1987A ring, but instead show a geometrically thin clumpy ring. The radial mass distribution and size scales of inhomogeneities in SBW1's ring closely resemble those in the SN1987A ring, but the more complete disk expected to reside at the base of the RT fingers is absent. This structure may explain why portions of the SN1987A ring between the hotspots have not yet brightened after more than 15 years. The model we suggest does not require a fast wind colliding with a previous red supergiant wind. More surprisingly, images of SBW1 also reveal diffuse emission filling the interior of the ring in H-alpha and thermal-IR emission; 190K dust dominates the 8-20 micron luminosity (but contains only 1e-5Msun). Cooler (85K dust resides in the equatorial ring itself (dust mass of 5e-3Msun). Diffuse emission extends inward to 1 arcsecond from the central star, where a paucity of emission suggests an inner hole excavated by the wind. We propose that diffuse emission inside the ring arises from an ionized flow of material photoevaporated from the dense ring, and it prevents the supergiant wind from advancing in the equator. This inner emission could correspond to a structure hypothesized to reside around SN1987A that was never directly detected. We suggest that photoionization can play an important dynamical role in shaping the ring nebula, and we speculate that this might help explain the origin of the polar rings around SN1987A. abridged.
We explore the connection between the local escape velocity, V_esc, and the stellar population properties in the ATLAS3D survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses of our galaxies. We are able to fit the full range of surface brightness profiles found in our sample, and in addition we reproduce the results of state-of-the-art photometry in the literature with residuals of 0.04 mags. We utilise these photometric models and SAURON integral-field spectroscopy, combined with Jeans dynamical modelling, to determine the local V_esc derived from the surface brightness. We find that the local V_esc is tightly correlated with the Mgb and Fe5015 linestrengths and optical colours, and anti-correlated with the Hbeta linestrength. In the case of the Mgb and Colour - V_esc relations we find that the relation within individual galaxies follows the global relation between different galaxies. We intentionally ignored any uncertain contribution due to dark matter since we are seeking an empirical description of stellar population gradients in early-type galaxies that is ideal for quantitative comparison with model predictions. We identify a population of galaxies that occur only at low V_esc that exhibit negative gradients in the Mgb - and Colour -V_esc relations. These galaxies typically have young central stellar populations and contain significant amounts of molecular gas and dust. Combining these results with N-body simulations of binary mergers we use the Mgb-V_esc relation to constrain the possible number of dry mergers experienced by the local early-type galaxy population - a typical massive ETG can have experienced only ~1.5 major mergers before becoming a significant outlier in the Mgb-V_esc relation. [Abridged]
We present Chandra X-ray measurements of the gas mass fraction out to r500 for a complete sample of the 35 most luminous clusters from the Brightest Cluster Sample and the Extended Brightest Cluster Sample at redshift z=0.15-0.30. The sample includes relaxed and unrelaxed clusters, and the data were analysed independently using two pipelines and two different models for the gas density and temperature. We measure an average of fgas(r500) = 0.163 +/- 0.032, which is in agreement with the cosmic baryon fraction (Omega_b / Omega_M = 0.167 +/- 0.006) at the 1-sigma level, after adding the stellar baryon fraction. Earlier studies reported gas mass fractions significantly lower than the cosmic baryon fraction at r500, and in some cases higher values that are consistent with the cosmic baryon fraction towards the virial radius.In this paper we show that the most X-ray luminous clusters in the redshift range z=0.15-0.30 have a gas mass fraction that is consistent with the cosmic value at r500.
Knowledge of late K and M dwarf metallicities can be used to guide planet searches and constrain planet formation models. However, the determination of metallicities of late-type stars is difficult because visible wavelength spectra of their cool atmospheres contain many overlapping absorption lines, preventing the measurement of equivalent widths. We present new methods, and improved calibrations of existing methods, to determine metallicities of late-K and M dwarfs from moderate resolution (1300 < R < 2000) visible and infrared spectra. We select a sample of 112 wide binary systems that contain a late-type companion to a solar-type primary star. Our sample includes 62 primary stars with previously published metallicities, as well as 50 stars with metallicities determined from our own observations. We use our sample to empirically determine which features in the spectrum of the companion are best correlated with the metallicity of the primary. We derive metallicity calibrations for different wavelength ranges, and show that it is possible to get metallicities reliable to < 0.10 dex using either visible, J, H, or K band spectra. Our calibrations are applicable to dwarfs with metallicities of -1.04 < [Fe/H]< +0.56 and spectral types from K7 to M5. Lastly, we use our sample of wide binaries to test and refine existing calibrations to determine M dwarf metallicities. We find that the {\zeta} parameter, which measures the ratio of TiO can CaH bands, is correlated with [Fe/H] for super-solar metallicities, and {\zeta} does not always correctly identify metal-poor M dwarfs. We also find that existing calibrations in the K and H band are quite reliable for stars with [Fe/H] > -0.5, but are less useful for more metal-poor stars.
We explore the cosmological constraints on the parameter w_dm of the dark matter barotropic equation of state (EoS) to investigate the "warmness" of the dark matter fluid. The model is composed by the dark matter and dark energy fluids in addition to the radiation and baryon components. We constrain the values of w_dm using the latest cosmological observations that measure the expansion history of the Universe. When w_dm is estimated together with the parameter w_de of the barotropic EoS of dark energy we found that the cosmological data favor a value of w_dm = 0.006 +- 0.001, suggesting a -warm- dark matter, and w_de= -1.11 +- 0.03$ that corresponds to a phantom dark energy, instead of favoring a cold dark matter and a cosmological constant (w_dm = 0, w_de = -1). When w_dm is estimated alone but assuming w_de = -1, -1.1, -0.9, we found w_dm = 0.009 +- 0.002, 0.006 +- 0.002, 0.012 +- 0.002 respectively, where the errors are at 3 sigma (99.73%), i.e., w_dm > 0 with at least 99.73% of confidence level. When (w_dm, \Omega_dm0) are constrained together, the best fit to data corresponds to (w_dm=0.005 +- 0.001, \Omega_dm0 = 0.223 +- 0.008) and with the assumption of w_de = -1.1 instead of a cosmological constant (i.e., w_de = -1). With these results we found evidence of w_dm > 0 suggesting a -warm- dark matter, independent of the assumed value for w_{\rm de}, but where values w_de < -1 are preferred by the observations instead of the cosmological constant. These constraints on w_dm are consistent with perturbative analyses done in previous works.
The primordial CMB at small angular scales is sensitive to the ionization and expansion history of the universe around the time of recombination. This dependence has been exploited to constrain the helium abundance and the effective number of relativistic species. Here we focus on allowed ionization fraction trajectories, $\Xe (z)$, by constraining low-order principal components of perturbations to the standard recombination scenario ($\Xe$-eigenmodes) in the circa 2011 SPT, ACT and WMAP7 data. Although the trajectories are statistically consistent with the standard recombination, we find that there is a tension similar to that found by varying the helium fraction. We find that the prior probabilities on the eigenamplitudes are substantially influenced by the requirement that $\Xe$ trajectories conserve electron number. We propose requiring a sufficient entropy decrease between posterior and prior marginalized distributions be used as an $\Xe$-mode selection criterion. We find that in the case of the 2011 SPT/ACT+WMAP7 data only two modes are constrainable, but upcoming ACTPol, Planck and SPTPol data will be able to test more modes and more precisely address the current tension.
To study the population properties of small, remote objects beyond Neptune's orbit in the outer solar system, of kilometer size or smaller, serendipitous occultation search is so far the only way. For hectometer-sized Trans-Neptunian Objects (TNOs), optical shadows actually disappear because of diffraction. Observations at shorter wave lengths are needed. Here we report the effort of TNO occultation search in X-rays using RXTE/PCA data of Sco X-1 taken from June 2007 to October 2011. No definite TNO occultation events were found in the 334 ks data. We investigate the detection efficiency dependence on the TNO size to better define the sensible size range of our approach and suggest upper limits to the TNO size distribution in the size range from 30 m to 300 m. A list of X-ray sources suitable for future larger facilities to observe is proposed.
Allan Sandage returned to the distance scale and the calibration of the Hubble constant again and again during his active life, experimenting with different distance indicators. In 1952 his proof of the high luminosity of Cepheids confirmed Baade's revision of the distance scale (H0 ~ 250 km/s/Mpc). During the next 25 years, he lowered the value to 75 and 55. Upon the arrival of the Hubble Space Telescope, he observed Cepheids to calibrate the mean luminosity of nearby Type Ia supernovae (SNe Ia) which, used as standard candles, led to the cosmic value of H0 = 62.3 +/- 1.3 +/- 5.0. Eventually he turned to the tip of the red-giant branch (TRGB) as a very powerful distance indicator. A compilation of 176 TRGB distances yielded a mean, very local value of H0 = 62.9 +/- 1.6 and shed light on the streaming velocities in the Local Supercluster. Moreover, TRGB distances are now available for six SNe Ia; if their mean luminosity is applied to distant SNe Ia, one obtains H0 = 64.6 +/- 1.6 +/- 2.0. The weighted mean of the two independent large-scale calibrations yields H0 = 64.1 km/s/Mpc within 3.6%.
We present the results of an optical photometric monitoring program of 10 extremely radio loud broad absorption line quasars (RL-BALQSOs) with radio-loudness parameter, R, greater than 100 and magnitude g_i < 19. Over an observing run of about 3.5-6.5 hour we found a clear detection of variability for one of our 10 radio-loud BALQSOs with the INOV duty cycle of 5.1 per cent, while on including the probable variable cases, a higher duty cycle of 35.1 per cent is found; which are very similar to the duty cycle of radio quiet broad absorption line quasars (RQ-BALQSOs). This low duty cycle of clear variability per cent in radio-loud sub-class of BALQSOs can be understood under the premise where BALs outflow may arise from large variety of viewing angles from the jet axis or perhaps being closer to the disc plane.
We present measurements of the optical broadband atmospheric extinction coefficients and the night sky brightness at the Xuyi Observational Station of Purple Mountain Observatory (PMO). The measurements are based on CCD imaging data taken in the Sloan Digital Sky Survey g, r and i bands with the Xuyi 1.04/1.20m Schmidt Telescope for the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center (XSTPS-GAC), the photometric part of the Digital Sky Survey of the Galactic Anti-center (DSS-GAC). The data were collected in more than 130 winter nights from 2009 to 2011. We find that the atmospheric extinction coefficients for the g, r and i bands are 0.70, 0.55 and 0.38 mag/airmass, respectively, based on observations taken in several photometric nights. The night sky brightness determined from images of good quality has median val- ues of 21.7, 20.8 and 20.0 mag/arcsec2 and reaches 22.1, 21.2 and 20.4 mag/arcsec2 under the best observing conditions for the g, r and i bands, respectively. The relatively large extinction coefficients compared with other good astronomical observing sites are mainly due to the relatively low elevation (i.e. 180 m) and high humidity of the Station.
Coronal mass ejections (CMEs) are powered by magnetic energy stored in electric currents in coronal magnetic fields, with the pre-CME field in balance between outward magnetic pressure of the proto-ejecta and inward magnetic tension from confining overlying fields. In studies of global, current-free coronal magnetic field models --- Potential-Field Source-Surface (PFSS) models --- it has been reported that model field strengths above flare sites tend to be weaker in when CMEs occur than when eruptions fail to occur. This suggests that potential field models might usefully quantify magnetic confinement. An implication of this idea is that a decrease in model field strength overlying a possible eruption site should correspond to diminished confinement, implying an eruption is more likely. We have searched for such an effect by {\em post facto} investigation of the time evolution of model field strengths above a sample of 10 eruption sites, which included both slow and fast CMEs. In most events we study, we find no statistically significant evolution in either: (i) the rate of magnetic field decay with height; (ii) the strength of overlying magnetic fields near 50 Mm; (iii) or the ratio of fluxes at low and high altitudes (below 1.1$R_{\odot}$, and between 1.1--1.5$R_{\odot}$, respectively). Instead, we found that overlying field strengths and overlying flux tend to increase slightly, and their rates of decay with height become slightly more gradual, consistent with increased confinement. Since CMEs occur regardless of whether the parameters we use to quantify confinement are increasing or decreasing, either: (i) these parameters do not accurately characterize confinement in CME source regions; or (ii) systematic evolution in the large-scale magnetic environment of CME source regions is not, by itself, a necessary condition for CMEs to occur; or both.
We present an algorithm for the detection of Low Surface Brightness (LSB) galaxies in images, called MARSIAA (MARkovian Software for Image Analysis in Astronomy), which is based on multi-scale Markovian modeling. MARSIAA can be applied simultaneously to different bands. It segments an image into a user-defined number of classes, according to their surface brightness and surroundings - typically, one or two classes contain the LSB structures. We have developed an algorithm, called DetectLSB, which allows the efficient identification of LSB galaxies from among the candidate sources selected by MARSIAA. To assess the robustness of our method, the method was applied to a set of 18 B and I band images (covering 1.3 square degrees in total) of the Virgo cluster. To further assess the completeness of the results of our method, both MARSIAA, SExtractor, and DetectLSB were applied to search for (i) mock Virgo LSB galaxies inserted into a set of deep Next Generation Virgo Survey (NGVS) gri-band subimages and (ii) Virgo LSB galaxies identified by eye in a full set of NGVS square degree gri images. MARSIAA/DetectLSB recovered ~20% more mock LSB galaxies and ~40% more LSB galaxies identified by eye than SExtractor/DetectLSB. With a 90% fraction of false positives from an entirely unsupervised pipeline, a completeness of 90% is reached for sources with r_e > 3" at a mean surface brightness level of mu_g=27.7 mag/arcsec^2 and a central surface brightness of mu^0 g=26.7 mag/arcsec^2. About 10% of the false positives are artifacts, the rest being background galaxies. We have found our method to be complementary to the application of matched filters and an optimized use of SExtractor, and to have the following advantages: it is scale-free, can be applied simultaneously to several bands, and is well adapted for crowded regions on the sky.
Recent measurements showed that the period derivative of the `high-B' radio pulsar PSR J1734-3333 is increasing with time. For neutron stars evolving with fallback disks, this rotational behavior is expected in certain phases of the long-term evolution. Using the same model as employed earlier to explain the evolution of anomalous X-ray pulsars and soft gamma-ray repeaters, we show that the period, the first and second period derivatives and the X-ray luminosity of this source can simultaneously acquire the observed values for a neutron star evolving with a fallback disk. We find that the required strength of the dipole field that can produce the source properties is in the range of $ 1 - 5 \times 10^{12}$ G on the pole of the neutron star. When the model source reaches the current state properties of PSR J1734-3333, accretion onto the star is not allowed yet, since the inner disk is not able to penetrate the light cylinder in this phase, allowing the source to operate as a regular radio pulsar. Our results imply that PSR J1734-3333 is at an age of $\sim 3 \times 10^4$ years. Such sources will have properties like the X-ray dim neutron stars or transient AXPs at a later epoch of weak accretion from the diminished fallback disk.
I present a simple scheme for the treatment of gravitational interactions on galactic scales. In analogy to known mechanisms of quantum field theory, I assume ad hoc that gravitation is mediated by virtual exchange particles - gravitons - with very small but non-zero masses. The resulting density and mass profiles are proportional to the mass of the gravitating body. The mass profile scales with the centripetal acceleration experienced by a test particle orbiting the central mass; this comes at the cost of postulating a universal characteristic acceleration a0 = 4.3*10^{-12} m/s^2 (or 8*pi*a0 = 1.1*10^{-10} m/s^2). The scheme predicts the asymptotic flattening of galactic rotation curves, the Tully-Fisher/Faber-Jackson relations, the mass discrepancy-acceleration relation of galaxies, the surface brightness-acceleration relation of galaxies, the kinematics of galaxy clusters, and "Renzo's rule" correctly; additional (dark) mass components are not required. Given that it is based on various ad-hoc assumptions, and given further limitations, the scheme I present is not yet a consistent theory of gravitation; rather, it is a "toy model" providing a convenient scaling law that simplifies the description of gravity on galactic scales.
Numerical simulations of convection driven rotating spherical shell dynamos have often been performed with rigid boundary conditions, as is appropriate for the metallic cores of terrestrial planets. Free-slip boundaries are more appropriate for dynamos in other astrophysical objects, such as gas-giants or stars. Using a set of 57 direct numerical simulations, we investigate the effect of free-slip boundary conditions on the scaling properties of heat flow, flow velocity and magnetic field strength and compare it with earlier results for rigid boundaries. We find that the nature of the mechanical boundary condition has only a minor influence on the scaling laws. We also find that although dipolar and multipolar dynamos exhibit approximately the same scaling exponents, there is an offset in the scaling pre-factors for velocity and magnetic field strength. We argue that the offset can be attributed to the differences in the zonal flow contribution between dipolar and multipolar dynamos.
Optical-infrared interferometry can provide direct geometrical measurements of the radii of Cepheids and/or reveal unknown binary companions of these stars. Such information is of great importance for a proper calibration of Period-Luminosity relations and for determining binary fraction among Cepheids. We observed the Cepheid X Sgr with VLTI/AMBER in order to confirm or disprove the presence of the hypothesized binary companion and to directly measure the mean stellar radius, possibly detecting its variation along the pulsation cycle. From AMBER observations in MR mode we performed a binary model fitting on the closure phase and a limb-darkened model fitting on the visibility. Our analysis indicates the presence of a point-like companion at a separation of 10.7 mas and 5.6 magK fainter than the primary, whose flux and position are sharply constrained by the data. The radius pulsation is not detected, whereas the average limb-darkened diameter results to be 1.48+/-0.08 mas, corresponding to 53+/-3 R_sun at a distance of 333.3 pc.
We report on the abundance of metals (Mg and Fe) in the intracluster medium (ICM) at the outskirts (0.2 r200 - 0.8 r200) of the Perseus cluster. The X-ray spectra were obtained in the Suzaku/XIS mapping observations of this region. We employ single temperature models to fit all the X-ray spectra. The ICM temperature smoothly decreases toward the outer region from 6 keV to 4 keV. The Fe abundance is uniformly distributed at the outskirts (~0.3 solar). The Mg abundance is ~1 solar at the outskirts. The solar ratios of Mg/Fe of the outskirts region (Mg/Fe ~4) are a factor of 4 larger than those of the central region. Various systematic effects, including the spatial fluctuations in the cosmic X-ray background, are taken into account and evaluated. These our results have not changed significantly.
The presence of matter with angular momentum, in the form of a fallback disk around a young isolated neutron star will determine its evolution. This leads to an understanding of many properties of different classes of young neutron stars, in particular a natural explanation for the period clustering of AXPs, SGRs and XDINs. The spindown or spinup properties of a neutron star are determined by the dipole component of the magnetic field. The natural possibility that magnetars and other neutron stars may have different strengths of the dipole and higher multipole components of the magnetic field is now actually required by observations on the spindown rates of some magnetars. This talk gives a broad overview and some applications of the fallback disk model to particular neutron stars. Salient points are: (i) A fallback disk has already been observed around the AXP 4U 0142+61 some years ago. (ii) The low observed spindown rate of the SGR 0418+5729 provides direct evidence that the dipole component of the field is in the $10^{12} G$ range. All properties of the SGR 0418+5729 at its present age can be explained by spindown under torques from a fallback disk. (iii) The anomalous braking index of PSR J1734-3333 can also be explained by the fallback disk model which gives the luminosity, period, period derivative {\em and} the period second derivative at the present age. (iv) These and all applications to a variety of other sources employ the same disk physics and evolution, differing only in the initial conditions of the disk.
Resonant amplification of magnetic fields in spacetimes with torsion are investigated by solving the Heisenberg-Ivanenko nonlinear spinor equation. It is shown that torsion is helicity dependent and that the magnetic fields can be resonantly amplified and that the spinor solution leads to an amplification of the magnetic field dependant of the sign of helicity. The QCD domain wall case with torsion is also investigated and the results compared with recent results by Forbes and Zhitnitski (PRL (2001)).
[Abridged] Classical novae (CNe) represent the main class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy M 31. Only three confirmed novae and three SSSs have been discovered in globular clusters (GCs) of any galaxy so far, of which one nova and two SSSs (including the nova) were found in M 31 GCs. To study the SSS state of CNe we carried out a high-cadence X-ray monitoring of the M 31 central area with XMM-Newton and Chandra. We analysed X-ray and optical data of a new transient X-ray source in the M 31 GC Bol 126, discovered serendipitously in Swift observations. Our optical data set was based on regular M 31 monitoring programmes from five different small telescopes. Additionally, we made use of Pan-STARRS 1 data obtained during the PAndromeda survey. Our observations reveal that the X-ray source in Bol 126 is the third SSS in an M 31 GC and can be confirmed as the second CN in the M 31 GC system. This nova is named M31N 2010-10f. Its properties in the X-ray and optical regimes agree with a massive white dwarf (M_WD >~ 1.3 M_sun) in the binary system. Incorporating the data on previously found (suspected) novae in M 31 GCs we used our high-cadence X-ray monitoring observations to estimate a tentative nova rate in the M 31 GC system of 0.05 /yr/GC. An optical estimate, based on the recent 10.5-year WeCAPP survey, gives a lower nova rate, which is compatible with the X-ray rate on the 95% confidence level. There is growing evidence that the nova rate in GCs is higher than expected from primordial binary formation and under conditions as in the field. Dynamical binary formation and/or additional accretion from the intracluster medium are possible scenarios for an increased nova rate, but observational confirmation for this enhancement has been absent, so far. Regular X-ray monitoring observations of M 31 provide a promising strategy to find these novae.
Nearby companions alter the evolution of massive stars in binary systems. Using a sample of Galactic massive stars in nearby young clusters, we simultaneously measure all intrinsic binary characteristics relevant to quantify the frequency and nature of binary interactions. We find a large intrinsic binary fraction, a strong preference for short orbital periods and a flat distribution for the mass-ratios. Our results do not support the presence of a significant peak of equal-mass `twin' binaries. As a result of the measured distributions, we find that over seventy per cent of all massive stars exchange mass with a companion. Such a rate greatly exceeds previous estimates and implies that the majority of massive stars have their evolution strongly affected by interaction with a nearby companion.
We present ALMA and VLA observations of the molecular and ionized gas at 0.1-0.3 arcsec resolution in the Class 0 protostellar system IRAS 16293-2422. These data clarify the origins of the protostellar outflows from the deeply embedded sources in this complex region. Source A2 is confirmed to be at the origin of the well known large scale north-east--south-west flow. The most recent VLA observations reveal a new ejection from that protostar, demonstrating that it drives an episodic jet. The central compact part of the other known large scale flow in the system, oriented roughly east-west, is well delineated by the CO(6-5) emission imaged with ALMA and is confirmed to be driven from within component A. Finally, a one-sided blueshifted bubble-like outflow structure is detected here for the first time from source B to the north-west of the system. Its very short dynamical timescale (~ 200 yr), low velocity, and moderate collimation support the idea that source B is the youngest object in the system, and possibly one of the youngest protostars known.
The Large Magellanic Cloud (LMC) hosts a rich and varied population of supernova remnants (SNRs). Optical, X-ray, and radio observations are required to identify these SNRs, as well as to ascertain the various processes responsible for the large array of physical characteristics observed. In this paper we attempted to confirm the candidate SNR [HP99] 1234, identified in X-rays with ROSAT, as a true SNR by supplementing these X-ray data with optical and radio observations. Optical data from the Magellanic Cloud Emission Line Survey (MCELS) and new radio data from the Molonglo Observatory Synthesis Telescope (MOST), in addition to the ROSAT X-ray data, were used to perform a morphological analysis of this candidate SNR. An approximately ellipsoidal shell of enhanced [SII], typical of an SNR ([SII]/Halpha > 0.4), was detected in the optical. This enhancement is coincident with faint radio emission at 36 cm. Using the available data we estimated the size of the remnant to be ~5.1' x 4.0' (~75 pc x 59 pc). However, the measurement along the major-axis was somewhat uncertain due to a lack of optical and radio emission at its extremities and the poor resolution of the X-ray data. Assuming this SNR is in the Sedov phase and adopting the ambient mass density of 1.2x10^-25 g cm^-3 measured in a nearby HII region, an age estimate of ~25 kyr was calculated for a canonical initial explosion energy of 10^51 erg. However, this age estimate should be treated cautiously due to uncertainties on the adopted parameters. Analysis of the local stellar population suggested a type Ia event as a precursor to this SNR, however, a core-collapse mechanism could not be ruled out due to the possibility of the progenitor being a runaway massive star. With the detection of X-ray, radio and optical line emission with enhanced [SII], this object was confirmed as an SNR and we assign the identifier MCSNR J0527-7104.
We present spectroscopic observations of 182 disk galaxies (96 in the cluster and 86 in the field environment) in the region of the Abell 901/902 multiple cluster system, which is located at a redshift of $z\sim 0.165$. The presence of substructures and non-Gaussian redshift distributions indicate that the cluster system is dynamically young and not in a virialized state. We find evidence for two important galaxy populations. \textit{Morphologically distorted galaxies} are probably subject to increased tidal interactions. They show pronounced rotation curve asymmetries at intermediate cluster-centric radii and low rest-frame peculiar velocities. \textit{Morphologically undistorted galaxies} show the strongest rotation curve asymmetries at high rest-frame velocities and low cluster-centric radii. Supposedly, this group is strongly affected by ram-pressure stripping due to interaction with the intra-cluster medium. Among the morphologically undistorted galaxies, dusty red galaxies have particularly strong rotation curve asymmetries, suggesting ram pressure is an important factor in these galaxies. Furthermore, dusty red galaxies on average have a bulge-to-total ratio higher by a factor of two than cluster blue cloud and field galaxies. The fraction of kinematically distorted galaxies is 75% higher in the cluster than in the field environment. This difference mainly stems from morphological undistorted galaxies, indicating a cluster-specific interaction process that only affects the gas kinematics but not the stellar morphology. Also the ratio between gas and stellar scale length is reduced for cluster galaxies compared to the field sample. Both findings could be best explained by ram-pressure effects.
We explore possibility of using the three dimensional bispectra of the Ly-alpha forest and the redshifted 21-cm signal from the post-reionization epoch to constrain primordial non-Gaussianity. Both these fields map out the large scale distribution of neutral hydrogen and maybe treated as tracers of the underlying dark matter field. We first present the general formalism for the auto and cross bispectrum of two arbitrary three dimensional biased tracers and then apply it to the specific case. We have modeled the 3D Ly-alpha transmitted flux field as a continuous tracer sampled along 1D skewers which corresponds to quasars sight lines. For the post reionization 21-cm signal we have used a linear bias model. We use a Fisher matrix analysis to present the first prediction for bounds on f_NL and the other bias parameters using the three dimensional 21-cm bispectrum and other cross bispectra. The bounds on f_NL depend on the survey volume, and the various observational noises. We have considered a BOSS like Ly-alpha survey where the average number density of quasars \bar{n} = 10^{-3} Mpc^{-2} and the spectra are measured at a 2-sigma level. For the 21-cm signal we have considered a 4000 hrs observation with a futuristic SKA like radio array. We find that bounds on f_NL obtained in our analysis (6 <\Delta f_NL < 65) is competitive with CMBR and galaxy surveys and may prove to be an important alternative approach towards constraining primordial physics using future data sets. Further, we have presented a hierarchy of power of the bispectrum-estimators towards detecting the f_NL. Given the quality of the data sets, one may use this method to optimally choose the right estimator and thereby provide better constraints on f_NL. This shall be important in the quest towards understanding the mechanism behind the generation of primordial perturbations.
The evolution of the non-adiabatic pressure perturbation during inflation driven by two scalar fields is studied numerically for three different types of models. In the first model, the fields have standard kinetic terms. The other two models considered feature non-canonical kinetic terms; the first containing two fields which are coupled via their kinetic terms, and the second where one field has the standard kinetic term with the other field being a DBI field. We find that the evolution and the final amplitude of the non-adiabatic pressure perturbation depends strongly on the kinetic terms.
The Encke Gap is a 320-km-wide opening in Saturn's outer A ring that contains the orbit of the small moon Pan and an array of dusty features composed of particles less than 100 microns across. In particular, there are three narrow ringlets in this region that are not longitudinally homogeneous, but instead contain series of bright clumps. Using images obtained by the Cassini spacecraft, we track the motions of these clumps and demonstrate that they do not follow the predicted trajectories of isolated ring particles moving under the influence of Saturn's and Pan's gravitational fields. We also examine the orbital properties of these ringlets by comparing images taken at different longitudes and times. We find evidence that the orbits of these particles have forced eccentricities induced by solar radiation pressure. In addition, the mean radial positions of the particles in these ringlets appear to vary with local co-rotating longitude, perhaps due to the combined action of drag forces, gravitational perturbations from Pan, and collisions among the ring particles. The dynamics of the dust within this gap therefore appears to be much more complex than previously appreciated.
We use the IRAM 30-m telescope to perform a sensitive search for CN N=2-1 in
42 T Tauri or Herbig Ae systems located mostly in the Taurus-Auriga region.
$^{13}$CO J=2-1 is observed simultaneously to indicate the level of confusion
with the surrounding molecular cloud. The bandpass also contains two
transitions of ortho-H$_2$CO, one of SO and the C$^{17}$O J=2-1 line which
provide complementary information on the nature of the emission.
While $^{13}$CO is in general dominated by residual emission from the cloud,
CN exhibits a high disk detection rate $> 50$% in our sample. We even report CN
detection in stars for which interferometric searches failed to detect
$^{12}$CO, presumably because of obscuration by a foreground, optically thick,
cloud. Comparison between CN and o-H$_2$CO or SO line profiles and intensities
divide the sample in two main categories. Sources with SO emission are bright
and have strong H$_2$CO emission, leading in general to [H$_2$CO/CN]$ > 0.5$.
Furthermore, their line profiles, combined with a priori information on the
objects, suggest that the emission is coming from outflows or envelopes rather
than from a circumstellar disk. On the other hand, most sources have
[H$_2$CO/CN]$ < 0.3$, no SO emission, and some of them exhibit clear
double-peaked profiles characteristics of rotating disks. In this second
category, CN is likely tracing the proto-planetary disks. From the line flux
and opacity derived from the hyperfine ratios, we constrain the outer radii of
the disks, which range from 300 to 600 AU. The overall gas disk detection rate
(including all molecular tracers) is $\sim 68%$, and decreases for fainter
continuum sources.
This study shows that gas disks, like dust disks, are ubiquitous around young
PMS stars in regions of isolated star formation, and that a large fraction of
them have $R > 300$ AU.
Context: A significantly higher incidence of strong (rest equivalent width W_r > 1 {\AA}) intervening Mg II absorption is observed along gamma-ray burst (GRB) sight-lines relative to those of quasar sight-lines. A geometrical explanation for this discrepancy has been suggested: the ratio of the beam size of the source to the characteristic size of a Mg II absorption system can influence the observed Mg II equivalent width, if these two sizes are comparable. Aims: We investigate whether the differing beam sizes of the continuum source and broad-line region of Sloan Digital Sky Survey (SDSS) quasars produce a discrepancy between the incidence of strong Mg II absorbers illuminated by the quasar continuum region and those of absorbers illuminated by both continuum and broad-line region light. Methods: We perform a semi-automated search for strong Mg II absorbers in the SDSS Data Release 7 quasar sample. The resulting strong Mg II absorber catalog is available online. We measure the sight-line number density of strong Mg II absorbers superimposed on and off the quasar C IV 1550 {\AA} and C III] 1909 {\AA} emission lines. Results: We see no difference in the sight-line number density of strong Mg II absorbers superimposed on quasar broad emission lines compared to those superimposed on continuum-dominated spectral regions. This suggests that the Mg II-absorbing clouds typically observed as intervening absorbers in quasar spectra are larger than the beam sizes of both the continuum-emitting regions and broad line-emitting regions in the centers of quasars, corresponding to a lower limit of the order of 10^17} cm for the characteristic size of a Mg II absorbing cloud.
High-precision spectrographs play a key role in exoplanet searches and Doppler asteroseismology using the radial velocity technique. The 1 m/s level of precision requires very high stability and uniformity of the illumination of the spectrograph. In fiber-fed spectrographs such as SOPHIE, the fiber-link scrambling properties are one of the main conditions for high precision. To significantly improve the radial velocity precision of the SOPHIE spectrograph, which was limited to 5-6 m/s, we implemented a piece of octagonal-section fiber in the fiber link. We present here the scientific validation of the upgrade of this instrument, demonstrating a real improvement. The upgraded instrument, renamed SOPHIE+, reaches radial velocity precision in the range of 1-2 m/s. It is now fully efficient for the detection of low-mass exoplanets down to 5-10 Earth mass and for the identification of acoustic modes down to a few tens of cm/s.
Classical novae are stellar explosions occurring in binary systems, consisting of a white dwarf and a main sequence companion. Thermonuclear runaways on the surface of massive white dwarfs, consisting of oxygen and neon, are believed to reach peak temperatures of several hundred million kelvin. These temperatures are strongly correlated with the underlying white dwarf mass. The observational counterparts of such models are likely associated with outbursts that show strong spectral lines of neon in their shells (neon novae). The goals of this work are to investigate how useful elemental abundances are for constraining the peak temperatures achieved during these outbursts and determine how robust "nova thermometers" are with respect to uncertain nuclear physics input. We present updated observed abundances in neon novae and perform a series of hydrodynamic simulations for several white dwarf masses. We find that the most useful thermometers, N/O, N/Al, O/S, S/Al, O/Na, Na/Al, O/P, and P/Al, are those with the steepest monotonic dependence on peak temperature. The sensitivity of these thermometers to thermonuclear reaction rate variations is explored using post-processing nucleosynthesis simulations. The ratios N/O, N/Al, O/Na, and Na/Al are robust, meaning they are minimally affected by uncertain rates. However, their dependence on peak temperature is relatively weak. The ratios O/S, S/Al, O/P, and P/Al reveal strong dependences on temperature and the poorly known 30P(p,g)31S rate. We compare our model predictions to neon nova observations and obtain the following estimates for the underlying white dwarf masses: 1.34-1.35 solar masses (V838 Her), 1.18-1.21 solar masses (V382 Vel), <1.3 solar masses (V693 CrA), <1.2 solar masses (LMC 1990#1), and <1.2 solar masses (QU Vul).
The origin of the bulk of cosmic rays (CRs) observed at Earth is the topic of a century long investigation, paved with successes and failures. From the energetic point of view, supernova remnants (SNRs) remain the most plausible sources of CRs up to rigidity ? 10^6-10^7 GV. This confidence somehow resulted in the construction of a paradigm, the so-called SNR paradigm: CRs are accelerated through di?usive shock acceleration in SNRs and propagate di?ffusively in the Galaxy in an energy dependent way. Qualitative confirmation of the SNR acceleration scenario has recently been provided by gamma ray and X-ray observations. Diff?usive propagation in the Galaxy is probed observationally through measurement of the secondary to primary nuclei flux ratios (such as B/C). There are however some weak points in the paradigm, which suggest that we are probably missing some physical ingredients in our models. The theory of diff?usive shock acceleration at SNR shocks predicts spectra of accelerated particles which are systematically too hard compared with the ones inferred from gamma ray observations. Moreover, hard injection spectra indirectly imply a steep energy dependence of the diffusion coefficient in the Galaxy, which in turn leads to anisotropy larger than the observed one. Moreover recent measurements of the flux of nuclei suggest that the spectra have a break at rigidity ? 200 GV, which does not sit well with the common wisdom in acceleration and propagation. In this paper I will review these new developments and suggest some possible implications.
RR Lyrae stars for a long time had the reputation of being rather simple pulsators, but the advent of high-precision space photometry has meanwhile changed this picture dramatically. This article summarizes the results obtained for two remarkable Blazhko RR Lyrae stars and discusses how our view of RR Lyrae stars has changed since the availability of ultra-precise satellite photometry as it is obtained by CoRoT and Kepler. Both stars, CoRoT 105288363 and V445 Lyrae, show a multitude of phenomena that were impossible to observe from the ground, either because of the small amplitude of the effect, or because uninterrupted long-term monitoring was required for a detection. Not only was it found that strong and irregular cycle-to-cycle changes of the Blazhko effect can occur, and that seemingly chaotic phenomena need to be accounted for when modeling the Blazhko effect, but also a rich spectrum of low-amplitude frequencies was detected in addition to the fundamental radial pusation in RRab stars. The so-called period doubling phenomenon, higher radial overtones and possibly also non-radial modes make RR Lyrae stars more multifaceted than previously thought. This article presents the various aspects of irregularity of the Blazhko effect, questioning its long-standing definition as a "periodic modulation", and also discusses the low-amplitude pulsation signatures that had been hidden in the noise of observations for centuries.
Radio-galaxy (RG) lobes contain relativistic electrons embedded in a tangled magnetic field that produce, in addition to low-frequency synchrotron radio emission, inverse-Compton scattering (ICS) of the cosmic microwave background (CMB) photons. This produces a relativistic, non-thermal Sunyaev-Zel'dovich effect (SZE). We study the spectral and spatial properties of the non-thermal SZE in a sample of radio galaxies and make predictions for their detectability in both the negative and the positive part of the SZE, with space experiments like Planck, OLIMPO, and Herschel-SPIRE. These cover a wide range of frequencies, from radio to sub-mm. We model the SZE in a general formalism that is equivalent to the relativistic covariant one and describe the electron population contained in the lobes of the radio galaxies with parameters derived from their radio observations, namely, flux, spectral index, and spatial extension. We further constrain the electron spectrum and the magnetic field of the RG lobes using X-ray, gamma-ray, and microwave archival observations. We determine the main spectral features of the SZE in RG lobes, namely, the minimum, the crossover, and the maximum of the SZE. We show that these typical spectral features fall in the frequency ranges probed by the available space experiments. We provide the most reliable predictions for the amplitude and spectral shape of the SZE in a sample of selected RGs with extended lobes. In three of these objects, we also derive an estimate of the magnetic field in the lobe at the muG level by combining radio (synchrotron) observations and X-ray (ICS) observations. These data, together with the WMAP upper limits, set constraints on the minimum momentum of the electrons residing in the RG lobes and allow realistic predictions for the visibility of their SZE to be derived with Planck, OLIMPO, and Herschel-SPIRE. [abridged]
We present new XMM-Newton observations of the northwest (NW) radio relic region in the cluster Abell 3667. We detect a jump in the X-ray surface brightness and X-ray temperature at the sharp outer edge of the radio relic which indicate that this is the location of a merger shock with a Mach number of about 2. Comparing the radio emission to the shock properties implies that approximately 0.2% of the dissipated shock kinetic energy goes into accelerating relativistic electrons. This is an order of magnitude smaller than the efficiency of shock acceleration in many Galactic supernova remnants, which may be due to the lower Mach numbers of cluster merger shocks. The X-ray and radio properties indicate that the magnetic field strength in the radio relic is >= 3 muG, which is a very large field at a projected distance of ~2.2 Mpc from the center of a cluster. The radio spectrum is relatively flat at the shock, and steepens dramatically with distance behind the shock. This is consistent with radiative losses by the electrons and the post-shock speed determined from the X-ray properties. The Cygnus A radio source is located in a merging cluster of galaxies. This appears to be an early-stage merger. Our recent Suzaku observation confirm the presence of a hot region between the two subclusters which agrees with the predicted shocked region. The high spectral resolution of the CCDs on Suzaku allowed us to measure the radial component of the merger velocity, Delta v_r \approx 2650 km/s.
The two papers referred to in the title, claiming the detection of a large-scale massive hot gaseous halo around the Galaxy, have generated a lot of confusion and unwarranted excitement (including public news coverage). However, the papers are seriously flawed in many aspects, including problematic analysis and assumptions, as well as mis-reading and mis-interpreting earlier studies, which are inconsistent with the claim. Here we show examples of such flaws.
We aim to improve our picture of the low chromosphere in the quiet-Sun internetwork by investigating the intensity, horizontal velocity, size and lifetime variations of small bright points (BPs; diameter smaller than 0.3 arcsec) observed in the Ca II H 3968 {\AA} passband along with their magnetic field parameters, derived from photospheric magnetograms. Several high-quality time series of disc-centre, quiet-Sun observations from the Sunrise balloon-borne solar telescope, with spatial resolution of around 100 km on the solar surface, have been analysed to study the dynamics of BPs observed in the Ca II H passband and their dependence on the photospheric vector magnetogram signal. Parameters such as horizontal velocity, diameter, intensity and lifetime histograms of the isolated internetwork and magnetic Ca II H BPs were determined. Mean values were found to be 2.2 km/s, 0.2 arcsec (150 km), 1.48 average Ca II H quiet-Sun and 673 sec, respectively. Interestingly, the brightness and the horizontal velocity of BPs are anti-correlated. Large excursions (pulses) in horizontal velocity, up to 15 km/s, are present in the trajectories of most BPs. These could excite kink waves travelling into the chromosphere and possibly the corona, which we estimate to carry an energy flux of 310 W/m^2, sufficient to heat the upper layers, although only marginally. The stable observing conditions of Sunrise and our technique for identifying and tracking BPs have allowed us to determine reliable parameters of these features in the internetwork. Thus we find, e.g., that they are considerably longer lived than previously thought. The large velocities are also reliable, and may excite kink waves. Although these wave are (marginally) energetic enough to heat the quiet corona, we expect a large additional contribution from larger magnetic elements populating the network and partly also the internetwork.
If broad absorption line (BAL) quasars represent a high covering fraction evolutionary state (even if this is not the sole factor governing the presence of BALs), it is expected that they should show an excess of mid-infrared radiation compared to normal quasars. Some previous studies have suggested that this is not the case. We perform the first analysis of the IR properties of radio-loud BAL quasars, using IR data from WISE and optical (rest-frame ultraviolet) data from SDSS, and compare the BAL quasar sample with a well-matched sample of unabsorbed quasars. We find a statistically significant excess in the mid- to near-infrared luminosities of BAL quasars, particularly at rest-frame wavelengths of 1.5 and 4 microns. Our sample was previously used to show that BALs are observed along many lines of sight towards quasars, but with an overabundance of more edge-on sources, suggesting that orientation factors into the appearance of BALs. The evidence here---of a difference in IR luminosities between BAL quasars and unabsorbed quasars---may be ascribed to evolution. This suggests that a merging of the current BAL paradigms is needed to fully describe the class.
We have used the PACS instrument on the Herschel Space Observatory to observe eight cataclysmic variables at 70 and 160 microns. Of these eight objects, only AM Her was detected. We have combined the Herschel results with ground-based, Spitzer, and WISE observations to construct spectral energy distributions for all of the targets. For the two dwarf novae in the sample, SS Cyg and U Gem, we find that their infrared luminosities are completely dominated by their secondary stars. For the two highly magnetic "polars" in our survey, AM Her and EF Eri, we find that their mid-infrared excesses, previously attributed to circumbinary dust emission, can be fully explained by cyclotron emission. The WISE light curves for both sources show large, orbitally modulated variations that are identically phased to their near-IR light curves. We propose that significant emission from the lowest cyclotron harmonics (n </= 3) is present in EF Eri and AM Her. Previously, such emission would have been presumed to be optically thick, and not provide significant orbitally modulated flux. This suggests that the accretion onto polars is more complicated than assumed in the simple models developed for these two sources. We develop a model for the near-/mid-IR light curves for WZ Sge with an L2 donor star that shows that the ellipsoidal variations from its secondary star are detected. We conclude that none of the targets surveyed have dusty circumbinary disks.
This paper examines the outflows associated with the interaction of a stellar magnetosphere with an accretion disk. In particular, we investigate the magnetospheric ejections (MEs) due to the expansion and reconnection of the field lines connecting the star with the disk. Our aim is to study the dynamical properties of the outflows and evaluate their impact on the angular momentum evolution of young protostars. Our models are based on axisymmetric time-dependent magneto-hydrodynamic simulations of the interaction of the dipolar magnetosphere of a rotating protostar with a viscous and resistive disk, using alpha prescriptions for the transport coefficients. Our simulations are designed in order to model: the accretion process and the formation of accretion funnels; the periodic inflation/reconnection of the magnetosphere and the associated MEs; the stellar wind. Similarly to a magnetic slingshot, MEs can be powered by the rotation of both the disk and the star so that they can efficiently remove angular momentum from both. Depending on the accretion rate, MEs can extract a relevant fraction of the accretion torque and, together with a weak but non-negligible stellar wind torque, can balance the spin-up due to accretion. When the disk truncation approaches the corotation radius, the system enters a "propeller" regime, where the torques exerted by the disk and the MEs can even balance the spin-up due to the stellar contraction. The MEs spin-down efficiency can be compared to other scenarios, such as the Ghosh & Lamb, X-wind or stellar wind models. Nevertheless, for all scenarios, an efficient spin-down torque requires a rather strong dipolar component, which has been seldom observed in classical T Tauri stars. A better analysis of the torques acting on the protostar must take into account non-axisymmetric and multipolar magnetic components consistent with observations.
It is anticipated that the large sky areas covered by planned wide-field weak lensing surveys will reduce statistical errors to such an extent that systematic errors will instead become the dominant source of uncertainty. It is therefore crucial to devise numerical methods to measure galaxy shapes with the least possible systematic errors. We present a simple "forward deconvolution" method, \emph{gfit}, to measure galaxy shapes given telescope and atmospheric smearings, in the presence of noise. The method consists in fitting a single 2D elliptical S\'ersic profile to the data, convolved with the point spread function. We applied \emph{gfit} to the data proposed in the GRavitational lEnsing Accuracy Testing 2010 (GREAT10) Galaxy Challenge. In spite of its simplicity, \emph{gfit} obtained the lowest additive bias {($\sqrt{\mathcal{A}}=0.057\times10^{-4}$)} on the shear power spectrum among twelve different methods and the second lowest multiplicative bias {($\mathcal{M}/2=0.583\times10^{-2}$)}. It remains that \emph{gfit} is a fitting method and is therefore affected by noise bias. However, the simplicity of the underlying galaxy model combined with the use of an efficient customized minimization algorithm allow very competitive performances, at least on the GREAT10 data, for a relatively low computing time.
The Pleiades is the best studied open cluster in the sky. It is one of the primary open clusters used to define the `zero-age main sequence,' and hence it serves as a cornerstone for programs which use main-sequence fitting to derive distances. This role is called into question by the `Pleiades distance controversy' - the distance to the Pleiades from Hipparcos of approximately 120 pc is significantly different from the distance of 133 pc derived from other techniques. To resolve this issue, we plan to use Very Long Baseline Interferometry to derive a new, independent trigonometric parallax distance to the Pleiades. In these proceedings we present our observational program and report some preliminary results.
We investigate constraints on the distribution of dark matter in the neighbourhood of the Galactic Centre that may eventually be attained with the high-resolution Event Horizon Telescope (EHT). The shadow of a black hole in vacuum is used to generate a toy model describing how dark matter affects the size of the shadow of the supermassive black hole located at the Galactic Centre. Observations by the EHT may constrain the properties of the dark matter distribution in a possible density spike around the black hole. Current uncertainties due to both the resolution of the telescope and the analysis of stellar orbits prevent one from discerning the effect of dark matter on the measured size of the shadow. The change in the size of the shadow induced by dark matter can be seen as an additional uncertainty in any test of general relativity that relies on using the angular size of the shadow to estimate the Schwarzschild radius of the black hole.
The ghost-free theory of massive gravity has exact solutions where the effective stress energy generated by the graviton mass term is a cosmological constant for any isotropic metric. Since they are exact, these solutions mimic a cosmological constant in the presence of any matter-induced isotropic metric perturbation. In the Stueckelberg formulation, this stress energy is carried entirely by the spatial Stueckelberg field. We show that any stress energy carried by fluctuations in the spatial field away from the exact solution always decays away in an expanding universe. However, the dynamics of the spatial Stueckelberg field perturbation depend on the background temporal Stueckelberg field, which is equivalent to the unitary gauge time coordinate. This dependence resolves an apparent conflict in the existing literature by showing that there is a special unitary time choice for which the field dynamics and energy density perturbations vanish identically. In general, the isotropic system has a single dynamical degree of freedom requiring two sets of initial data; however, only one of these initial data choices will affect the observable metric. Finally, we construct cosmological solutions with a well-defined perturbative initial value formulation and comment on alternate solutions that evolve to singularities.
Higher-form flux that extends in all 3+1 dimensions of spacetime is a source of positive vacuum energy that can drive meta-stable eternal inflation. If the flux also threads compact extra dimensions, the spontaneous nucleation of a bubble of brane charged under the flux can trigger a classical cascade that steadily unwinds many units of flux, gradually decreasing the vacuum energy while inflating the bubble, until the cascade ends in the self-annihilation of the brane into radiation. With an initial number of flux quanta Q_{0} \simgeq N, this can result in N efolds of inflationary expansion while producing a scale-invariant spectrum of adiabatic density perturbations with amplitude and tilt consistent with observation. The power spectrum has an oscillatory component that does not decay away during inflation, relatively large tensor power, and interesting non-Gaussianities. Unwinding inflation fits naturally into the string landscape, and our preliminary conclusion is that consistency with observation can be attained without fine-tuning the string parameters. The initial conditions necessary for the unwinding phase are produced automatically by bubble formation, so long as the critical radius of the bubble is smaller than at least one of the compact dimensions threaded by flux.
We suggest a new perspective on the Cosmological Constant Problem by scrutinizing its standard formulation. In classical and quantum mechanics without gravity, there is no definition of the zero point of energy. Furthermore, the Casimir effect only measures how the vacuum energy changes as one varies a geometric modulus. This leads us to propose that the physical vacuum energy in a Friedman-Lemaitre-Robertson-Walker expanding universe only depends on the time variation of the scale factor a(t). Equivalently, requiring that empty Minkowski space is stable is a principle that fixes the ambiguity in the zero point energy. We describe two different choices of vacuum, one of which is consistent with the current universe consisting only of matter and vacuum energy. The resulting vacuum energy density is proportional to (k_c H_0)^2, where k_c is a momentum cut-off and H_0 is the Hubble constant; for a cut-off close to the Planck scale, values of the vacuum energy density in agreement with astrophysical measurements are obtained. Another choice of vacuum is more relevant to the early universe consisting of only radiation and vacuum energy, and we suggest it as a possible model of inflation.
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Broad absorption lines (BALs) in quasar spectra are prominent signatures of high-velocity outflows, which might be present in all quasars and could be a major contributor to feedback to galaxy evolution. Studying the variability in these BALs allows us to further our understanding of the structure, evolution, and basic physical properties of the outflows. This is the third paper in a series on a monitoring programme of 24 luminous BAL quasars at redshifts 1.2 < z < 2.9. We focus here on the time-scales of variability in CIV 1549A BALs in our full multi-epoch sample, which covers time-scales from 0.02-8.7 yr in the quasar rest-frame. Our sample contains up to 13 epochs of data per quasar, with an average of 7 epochs per quasar. We find that both the incidence and the amplitude of variability are greater across longer time-scales. Part of our monitoring programme specifically targeted half of these BAL quasars at rest-frame time-scales <2 months. This revealed variability down to the shortest time-scales we probe (8-10 days). Observed variations in only portions of BAL troughs or in lines that are optically thick suggest that at least some of these changes are caused by clouds (or some type of outflow substructures) moving across our lines of sight. In this crossing cloud scenario, the variability times constrain both the crossing speeds and the absorber locations. Typical variability times of order ~1 year indicate crossing speeds of a few thousand km/s and radial distances near ~1 pc from the central black hole. However, the most rapid BAL changes occurring in 8-10 days require crossing speeds of 17 000 - 84 000 km/s and radial distances of only 0.001-0.02 pc. These speeds are similar to or greater than the observed radial outflow speeds, and the inferred locations are within the nominal radius of the broad emission line region.
We present IRIS, a new generic three-dimensional (3D) spectral radiative transfer code that generates synthetic spectra, or images. It can be used as a diagnostic tool for comparison with astrophysical observations or laboratory astrophysics experiments. We have developed a 3D short-characteristic solver that works with a 3D nonuniform Cartesian grid. We have implemented a piecewise cubic, locally monotonic, interpolation technique that dramatically reduces the numerical diffusion effect. The code takes into account the velocity gradient effect resulting in gradual Doppler shifts of photon frequencies and subsequent alterations of spectral line profiles. It can also handle periodic boundary conditions. This first version of the code assumes Local Thermodynamic Equilibrium (LTE) and no scattering. The opacities and source functions are specified by the user. In the near future, the capabilities of IRIS will be extended to allow for non-LTE and scattering modeling. IRIS has been validated through a number of tests. We provide the results for the most relevant ones, in particular a searchlight beam test, a comparison with a 1D plane-parallel model, and a test of the velocity gradient effect. IRIS is a generic code to address a wide variety of astrophysical issues applied to different objects or structures, such as accretion shocks, jets in young stellar objects, stellar atmospheres, exoplanet atmospheres, accretion disks, rotating stellar winds, cosmological structures. It can also be applied to model laboratory astrophysics experiments, such as radiative shocks produced with high power lasers.
Massive black holes in galactic nuclei vary their mass M and spin vector J due to accretion. In this study we relax, for the first time, the assumption that accretion can be either chaotic, i.e. when the accretion episodes are randomly and isotropically oriented, or coherent, i.e. when they occur all in a preferred plane. Instead, we consider different degrees of anisotropy in the fueling, never confining to accretion events on a fixed direction. We follow the black hole growth evolving contemporarily mass, spin modulus a and spin direction. We discover the occurrence of two regimes. An early phase (M <~ 10 million solar masses) in which rapid alignment of the black hole spin direction to the disk angular momentum in each single episode leads to erratic changes in the black hole spin orientation and at the same time to large spins (a ~ 0.8). A second phase starts when the black hole mass increases above >~ 10 million solar masses and the accretion disks carry less mass and angular momentum relatively to the hole. In the absence of a preferential direction the black holes tend to spin-down in this phase. However, when a modest degree of anisotropy in the fueling process (still far from being coherent) is present, the black hole spin can increase up to a ~ 1 for very massive black holes (M >~ 100 million solar masses), and its direction is stable over the many accretion cycles. We discuss the implications that our results have in the realm of the observations of black hole spin and jet orientations.
Sloshing cold fronts (CFs) arise from minor merger triggered gas sloshing. Their detailed structure depends on the properties of the intra-cluster medium (ICM): hydrodynamical simulations predict the CFs to be distorted by Kelvin-Helmholtz instabilities (KHIs), but aligned magnetic fields, viscosity, or thermal conduction can suppress the KHIs. Thus, observing the detailed structure of sloshing CFs can be used to constrain these ICM properties. Both smooth and distorted sloshing CFs have been observed, indicating that the KHI is suppressed in some clusters, but not in all. Consequently, we need to address at least some sloshing clusters individually before drawing general conclusions about the ICM properties. We present the first detailed attempt to constrain the ICM properties in a specific cluster from the structure of its sloshing CF. Proximity and brightness make the Virgo cluster an ideal target. We combine observations and Virgo-specific hydrodynamical sloshing simulations. Here we focus on a Spitzer-like temperature dependent viscosity as a mechanism to suppress the KHI, but discuss the alternative mechanisms in detail. We identify the CF at 90 kpc north and north-east of the Virgo center as the best location in the cluster to observe a possible KHI suppression. For viscosities $\gtrsim$ 10% of the Spitzer value KHIs at this CF are suppressed. We describe in detail the observable signatures at low and high viscosities, i.e. in the presence or absence of KHIs. We find indications for a low ICM viscosity in archival XMM-Newton data and demonstrate the detectability of the predicted features in deep Chandra observations.
The evolution of small systems such as dwarf spheroidal galaxies (dSph) is
likely to have been a balance between external environmental effects and
internal processes within their own relatively shallow potential wells.
Assessing how strong such environmental interactions may have been is therefore
an important element in understanding the baryonic evolution of dSphs and their
derived dark matter distribution.
Here we present results from a wide-area CTIO/MOSAIC II photometric survey of
the Carina dSph, reaching down to about two magnitudes below the oldest main
sequence turn-off (MSTO). This data-set enables us to trace the structure of
Carina in detail out to very large distances from its center, and as a function
of stellar age.
We observe the presence of an extended structure made up primarily of ancient
MSTO stars, at distances between 25arcmin-60arcmin from Carina's center,
confirming results in the literature that Carina extends well beyond its
nominal tidal radius.
The large number statistics of our survey reveals features such as isophote
twists and tails that had gone undetected in other previous shallower surveys.
This is the first time that such unambiguous signs of tidal disruption have
been found in a Milky Way "classical" dwarf other than Sagittarius.
We also demonstrate the presence of a negative age gradient in Carina
directly from its MSTOs, and trace it out to very large distances from the
galaxy center. The signs of interaction with the Milky Way make it unclear
whether the age gradient was already in place before Carina underwent tidal
disruption.
In a previous paper we presented the Directed Follow-Up (DFU) approach, which we suggested can be used to efficiently augment low-cadence photometric surveys in a way that will optimize the chances to detect transiting exoplanets. In this paper we present preliminary tests of applying the DFU approach to the future ESA space mission Gaia. We demonstrate the strategy application to Gaia photometry through a few simulated cases of known transiting planets, using Gaia expected performance and current design. We show that despite the low cadence observations DFU, when tailored for Gaia's scanning law, can facilitate detection of transiting planets with ground-based observations, even during the lifetime of the mission. We conclude that Gaia photometry, although not optimized for transit detection, should not be ignored in the search of transiting planets. With a suitable ground-based follow-up network it can make an important contribution to this search.
We observed nine primary transits of the hot Jupiter TrES-3b in several optical and near-UV photometric bands from 2009 June to 2012 April in an attempt to detect its magnetic field. Vidotto, Jardine and Helling suggest that the magnetic field of TrES-3b can be constrained if its near-UV light curve shows an early ingress compared to its optical light curve, while its egress remains unaffected. Predicted magnetic field strengths of Jupiter-like planets should range between 8 G and 30 G. Using these magnetic field values and an assumed B_star of 100 G, the Vidotto et al. method predicts a timing difference of 5-11 min. We did not detect an early ingress in our three nights of near-UV observations, despite an average cadence of 68 s and an average photometric precision of 3.7 mmag. However, we determined an upper limit of TrES-3b's magnetic field strength to range between 0.013 and 1.3 G (for a 1-100 G magnetic field strength range for the host star, TrES-3) using a timing difference of 138 s derived from the Nyquist-Shannon sampling theorem. To verify our results of an abnormally small magnetic field strength for TrES-3b and to further constrain the techniques of Vidotto et al., we propose future observations of TrES-3b with other platforms capable of achieving a shorter near-UV cadence. We also present a refinement of the physical parameters of TrES-3b, an updated ephemeris and its first published near-UV light curve. We find that the near-UV planetary radius of Rp = 1.386+0.248-0.144 RJup is consistent with the planet's optical radius.
We present a high-performance, graphics processing unit (GPU)-based framework for the efficient analysis and visualization of (nearly) terabyte (TB)-sized 3-dimensional images. Using a cluster of 96 GPUs, we demonstrate for a 0.5 TB image: (1) volume rendering using an arbitrary transfer function at 7--10 frames per second; (2) computation of basic global image statistics such as the mean intensity and standard deviation in 1.7 s; (3) evaluation of the image histogram in 4 s; and (4) evaluation of the global image median intensity in just 45 s. Our measured results correspond to a raw computational throughput approaching one teravoxel per second, and are 10--100 times faster than the best possible performance with traditional single-node, multi-core CPU implementations. A scalability analysis shows the framework will scale well to images sized 1 TB and beyond. Other parallel data analysis algorithms can be added to the framework with relative ease, and accordingly, we present our framework as a possible solution to the image analysis and visualization requirements of next-generation telescopes, including the forthcoming Square Kilometre Array pathfinder radiotelescopes.
Debris disks have been found primarily around intermediate and solar mass stars (spectral types A-K) but rarely around low mass M-type stars. We have spatially resolved a debris disk around the remarkable M3-type star GJ581 hosting multiple planets using deep PACS images at 70, 100 and 160 microns as part of the DEBRIS Program on the Herschel Space Observatory. This is the second spatially resolved debris disk found around an M-type star, after the one surrounding the young star AU Mic (12 Myr). However, GJ 581 is much older (2-8 Gyr), and is X-ray quiet in the ROSAT data. We fit an axisymmetric model of the disk to the three PACS images and found that the best fit model is for a disk extending radially from 25+/-12 AU to more than 60 AU. Such a cold disk is reminiscent of the Kuiper Belt but it surrounds a low mass star (0.3 M_sol) and its fractional dust luminosity L_dust/L_* of \sim 10^-4 is much higher. The inclination limits of the disk found in our analysis make the masses of the planets small enough to ensure the long-term stability of the system according to some dynamical simulations. The disk is collisionally dominated down to submicron-sized grains and the dust cannot be expelled from the system by radiation or wind pressures because of the low luminosity and low X-ray luminosity of GJ581. We suggest that the correlation between low-mass planets and debris disks recently found for G-type stars also applies to M-type stars.Finally, the known planets, of low masses and orbiting within 0.3 AU from the star, cannot dynamically perturb the disk over the age of the star, suggesting that an additional planet exists at larger distance that is stirring the disk to replenish the dust.
Different formulations of MOND predict somewhat different rotation curves for the same mass distribution. Here I consider a global attribute of the rotation curve that might provide a convenient discriminant between theories when applied to isolated, pure-disk galaxies that are everywhere deep in the MOND regime. This parameter is Q=<V^2>/V0^2, where <V^2> is the mean squared rotational speed of the galaxy, and V0 is the asymptotic (constant) rotational speed. The comparison between the observed and predicted values of Q is oblivious to the distance, the inclination, the mass, and the size of the disk, and to the form of the interpolating function. For the known modified-gravity theories Q is predicted to be a universal constant (independent of the mass distribution in the disk): Q=2/3. The predicted Q value for modified-inertia theories does depend on the mass distribution. However, surprisingly, I find here that it varies only little among a very wide range of mass distributions, Q=0.73+-0.01. While the difference between the theories amounts to only about 5 percent in the predicted RMS velocity, a good enough sample of galaxies may provide the first discerning test between the two classes of theories.
A thorough search of the sky exposed at the Pierre Auger Cosmic Ray Observatory reveals no statistically significant excess of events in any small solid angle that would be indicative of a flux of neutral particles from a discrete source. The search covers from -90 to +15 degrees in declination using four different energy ranges above 1 EeV (10^18 eV). The method used in this search is more sensitive to neutrons than to photons. The upper limit on a neutron flux is derived for a dense grid of directions for each of the four energy ranges. These results constrain scenarios for the production of ultra-high energy cosmic rays in the Galaxy.
This paper provides a framework for incorporation of the wavefront sensor
sensor measurements in the context of observing modes in which the science
camera takes very short exposures. In this formulation, the wavefront sensor
measurements provide a means to jointly the static speckle and the planetary
signal. For simplicity, the mathematical development assumes a simple optical
system with an idealized Lyot coronagraph. Unlike currently used methods, in
which increasing the observation time beyond a certain threshold is useless,
this method produces estimates whose error covariances are inversely
proportional to the observation time due to the fact that the (quasi-)static
speckle and planetary emission are jointly estimated. The method can easily be
extended to include angular (due to diurnal field rotation) and spectral
diversity.
Numerical experiments are performed with wavefront data from the AEOS
Adaptive Optics System sensing at 850 nm. These experiments assume a science
camera wavelength of $2.2 \mu$, that the measured wavefronts are exact, an
ideal coronagraph, and a Gaussian approximation of shot-noise. A number of
static aberrations are introduced, including one with a spatial frequency
exactly corresponding the planet location. Using only 4 seconds of observation
time, a planetary intensity of $\sim 0.2$ photons/millisecond, a stellar
intensity of $\sim 9$ photons/millisecond/pixel at the planet's location, the
short-exposure estimation method recovers the correct amplitudes of all static
aberrations as well the correct planet brightness with a contrast ratio of
$10^{-6}$ with 17% accuracy. The ideal coronagraph itself provides about 95%
extinction in the frames with the highest Strehl ratios.
The lowest frequency band (70 - 450 MHz) of the Square Kilometre Array will consist of sparse aperture arrays grouped into geographically-localised patches, or stations. Signals from thousands of antennas in each station will be beamformed to produce station beams which form the inputs for the central correlator. Two-stage beamforming within stations can reduce SKA-low signal processing load and costs, but has not been previously explored for the irregular station layouts now favoured in radio astronomy arrays. This paper illustrates the effects of two-stage beamforming on sidelobes and effective area, for two representative station layouts (regular and irregular gridded tile on an irregular station). The performance is compared with a single-stage, irregular station. The inner sidelobe levels do not change significantly between layouts, but the more distant sidelobes are affected by the tile layouts; regular tile creates diffuse, but regular, grating lobes. With very sparse arrays, the station effective area is similar between layouts. At lower frequencies, the regular tile significantly reduces effective area, hence sensitivity. The effective area is highest for a two-stage irregular station, but it requires a larger station extent than the other two layouts. Although there are cost benefits for stations with two-stage beamforming, we conclude that more accurate station modelling, and SKA-low configuration specifications, are required before design finalisation.
Effects of light millicharged dark matter particles on primordial nucleosynthesis are considered. It is shown that if the mass of such particles is much smaller than the electron mass, they lead to strong overproduction of Helium-4. An agreement with observations can be achieved by non-vanishing lepton asymmetry. Baryon-to-photon ratio at BBN and neutrino-to-photon ratio both at BBN and at recombination are noticeably different as compared to the standard cosmological model. The latter ratio and possible lepton asymmetry could be checked by Planck. For higher mass of new particles the effect is much less pronounced and may even have opposite sign.
Turbulence is thought to be a key driver of the evolution of protoplanetary
disks, regulating the mass accretion process, the transport of angular
momentum, and the growth of dust particles.
We intend to determine the magnitude of the turbulent motions in the outer
parts (> 100 AU) of the disk surrounding DM Tau. Turbulent motions can be
constrained by measuring the nonthermal broadening of line emission from heavy
molecules. We used the IRAM Plateau de Bure interferometer to study emission
from the CS molecule in the disk of DM Tau. High spatial (1.4 x 1 ") and
spectral resolution (0.126 km/s) CS J=3-2 images provide constraints on the
molecule distribution and velocity structure of the disk. A low sensitivity CS
J=5-4 image was used in conjunction to evaluate the excitation conditions. We
analyzed the data in terms of two parametric disk models, and compared the
results with detailed time-dependent chemical simulations.
The CS data confirm the relatively low temperature suggested by observations
of other simple molecules. The intrinsic linewidth derived from the CS J=3-2
data is much larger than expected from pure thermal broadening. The magnitude
of the derived nonthermal component depends only weakly on assumptions about
the location of the CS molecules with respect to the disk plane. Our results
indicate turbulence with a Mach number around 0.4 - 0.5 in the molecular layer.
Geometrical constraints suggest that this layer is located near one scale
height, in reasonable agreement with chemical model predictions.
Asymptotic giant branch (AGB) stars with low initial mass (1 - 3 Msun) are responsible for the production of neutron-capture elements through the main s-process (main slow neutron capture process). The major neutron source is 13C(alpha, n)16O, which burns radiatively during the interpulse periods at about 8 keV and produces a rather low neutron density (10^7 n/cm^3). The second neutron source 22Ne(alpha, n)25Mg, partially activated during the convective thermal pulses when the energy reaches about 23 keV, gives rise to a small neutron exposure but a peaked neutron density (Nn(peak) > 10^11 n/cm^3). At metallicities close to solar, it does not substantially change the final s-process abundances, but mainly affects the isotopic ratios near s-path branchings sensitive to the neutron density. We examine the effect of the present uncertainties of the two neutron sources operating in AGB stars, as well as the competition with the 22Ne(alpha, gamma)26Mg reaction. The analysis is carried out on AGB the main-s process component (reproduced by an average between M(AGB; ini) = 1.5 and 3 Msun at half solar metallicity, see Arlandini et al. 1999), using a set of updated nucleosynthesis models. Major effects are seen close to the branching points. In particular, 13C(alpha, n)16O mainly affects 86Kr and 87Rb owing to the branching at 85Kr, while small variations are shown for heavy isotopes by decreasing or increasing our adopted rate by a factor of 2 - 3. By changing our 22Ne(alpha, n)25Mg rate within a factor of 2, a plausible reproduction of solar s-only isotopes is still obtained. We provide a general overview of the major consequences of these variations on the s-path. A complete description of each branching will be presented in Bisterzo et al., in preparation.
We present the status of LAUE, a project supported by the Italian Space Agency (ASI), and devoted to develop Laue lenses with long focal length (up to 100 meters), for hard X--/soft gamma--ray astronomy (80-600 keV). Thanks to their focusing capability, the design goal is to improve the sensitivity of the current instrumention in the above energy band by 2 orders of magnitude, down to a few times $10^{-8}$ photons/(cm$^2$ s keV).
The first stars are the key to the formation of primitive galaxies, early cosmological reionization and chemical enrichment, and the origin of supermassive black holes. Unfortunately, in spite of their extreme luminosities, individual Population III stars will likely remain beyond the reach of direct observation for decades to come. However, their properties could be revealed by their supernova explosions, which may soon be detected by a new generation of NIR observatories such as JWST and WFIRST. We present light curves and spectra for Pop III pair-instability supernovae calculated with the Los Alamos radiation hydrodynamics code RAGE. Our numerical simulations account for the interaction of the blast with realistic circumstellar envelopes, the opacity of the envelope, and Lyman absorption by the neutral IGM at high redshift, all of which are crucial to computing the NIR signatures of the first cosmic explosions. We find that JWST will detect pair-instability supernovae out to z > 30, WFIRST will detect them in all-sky surveys out to z ~ 15 - 20 and LSST and Pan-STARRS will find them at z ~ 7 - 8. The discovery of these ancient explosions will probe the first stellar populations and reveal the existence of primitive galaxies that might not otherwise have been detected.
Molecular hydrogen is the most abundant molecule in the universe. A large fraction of H2 forms by association of hydrogen atoms adsorbed on polycyclic aromatic hydrocarbons (PAHs), where formation rates depend crucially on the H sticking probability. We have experimentally studied PAH hydrogenation by exposing coronene cations, confined in a radiofrequency ion trap, to gas phase atomic hydrogen. A systematic increase of the number of H atoms adsorbed on the coronene with the time of exposure is observed. Odd coronene hydrogenation states dominate the mass spectrum up to 11 H atoms attached. This indicates the presence of a barrier preventing H attachment to these molecular systems. For the second and fourth hydrogenation, barrier heights of 72 +- 6 meV and 40 +- 10 meV, respectively are found which is in good agreement with theoretical predictions for the hydrogenation of neutral PAHs. Our experiments however prove that the barrier does not vanish for higher hydrogenation states. These results imply that PAH cations, as their neutral counterparts, exist in highly hydrogenated forms in the interstellar medium. Due to this catalytic activity, PAH cations and neutrals seem to contribute similarly to the formation of H2.
We report about new episode of decretion disk formation in the IGR J06074+2205 system. Obtained spectral data gives us opportunity to measure peak separation in double-peaked H\alpha\ line as 408+/-55 km/s and hence obtain disk radii as 1.6 star radii. All these facts may says about possible X-ray activity of IGR J06074+2205 in the nearest future.
In the context of the LAUE project devoted to build a long focal length focusing optics for soft gamma-ray astronomy (70/100 keV to $>$600 keV), we present results of simulation of a Laue lens, based on bent crystals in different assembling configurations (quasi-mosaic and reflection-like geometries). The main aim is to significantly overcome the sensitivity limits of the current generation of gamma-ray telescopes and improve the imaging capability.
We have recently developed a coupled chemistry-emission model for the green and red-doublet emissions of atomic oxygen on comet Hyakutake. In the present work we applied our model to comet Hale-Bopp, which had an order of magnitude higher H2O production rate than comet Hyakutake, to evaluate the photochemistry associated with the production and loss of O(1S) and O(1D) atoms and emission processes of green and red-doublet lines. We present the wavelength-dependent photo-attenuation rates for different photodissociation processes forming O(1S) and O(1D). The calculated radiative efficiency profiles of O(1S) and O(1D) atoms show that in comet Hale-Bopp the green and red-doublet emissions are emitted mostly above radial distances of 10^3 and 10^4 km, respectively. The model calculated [OI] 6300 A emission surface brightness and average intensity over the Fabry-P{\'e}rot spectrometer field of view are consistent with the observation of Morgenthaler et al. (2001), while the intensity ratio of green to red-doublet emission is in agreement with the observation of Zhang et al. (2001). In comet Hale-Bopp, for cometocentric distances less than 10^5 km, the intensity of [OI] 6300 A line is mainly governed by photodissociation of H2O. Beyond 10^5 km, O(1D) production is dominated by photodissociation of the water photochemical daughter product OH. Whereas the [OI] 5577 A emission line is controlled by photodissociation of both H2O and CO2. The calculated mean excess energy in various photodissociation processes show that the photodissociation of CO2 can produce O(1S) atoms with higher excess velocity compared to the photodissociation of H2O. Thus, our model calculations suggest that involvement of multiple sources in the formation of O(1S) could be a reason for the larger width of green line than that of red-doublet emission lines observed in several comets.
In the context of the LAUE project devoted to build a long focal-length focusing optics for soft $\gamma$-ray astronomy (80 - 600 keV), we present the results of reflectivity measurements of bent crystals in different configurations, obtained by bending perfect or mosaic flat crystals. We also compare these results with those obtained using flat crystals. The measurements were performed using the K$\alpha$ line of the Tungsten anode of the X-ray tube used in the LARIX facility of the University of Ferrara. These results are finalized to select the best materials and to optimize the thickness of the crystal tiles that will be used for building a Laue lens petal which is a part of an entire Laue lens, with 20 m focal length and 100-300 keV passband. The final goal of the LAUE project is overcome, by at least 2 orders of magnitude, the sensitivity limits of the current generation of $\gamma$-ray telescopes, and to improve the current $\gamma$-ray imaging capability.
The spatial variation of the colour of a galaxy may introduce a bias in the
measurement of its shape if the PSF profile depends on wavelength. We study how
this bias depends on the properties of the PSF and the galaxies themselves. The
bias depends on the scales used to estimate the shape, which may be used to
optimise methods to reduce the bias. Here we develop a general approach to
quantify the bias. Although applicable to any weak lensing survey, we focus on
the implications for the ESA Euclid mission.
Based on our study of synthetic galaxies we find that the bias is a few times
10^-3 for a typical galaxy observed by Euclid. Consequently, it cannot be
neglected and needs to be accounted for. We demonstrate how one can do so using
spatially resolved observations of galaxies in two filters. We show that HST
observations in the F606W and F814W filters allow us to model and reduce the
bias by an order of magnitude, sufficient to meet Euclid's scientific
requirements. The precision of the correction is ultimately determined by the
number of galaxies for which spatially-resolved observations in at least two
filters are available. We use results from the Millennium Simulation to
demonstrate that archival HST data will be sufficient for the tomographic
cosmic shear analysis with the Euclid dataset.
We investigate in detail a model where the curvaton is coupled to the Standard Model higgs. Parametric resonance might be expected to cause a fast decay of the curvaton, so that it would not have time to build up the curvature perturbation. However, we show that this is not the case, and that the resonant decay of the curvaton may be delayed even down to electroweak symmetry breaking. This delay is due to the coupling of the higgs to the thermal background, which is formed by the Standard Model degrees of freedom created from the inflaton decay. We establish the occurrence of the delay by considering the curvaton evolution and the structure of the higgs resonances. We then provide analytical expressions for the delay time, and for the subsequent resonant production of the higgs, which ultimately leads to the curvaton effective decay width. Contrary to expectations, it is possible to obtain the observed curvature perturbation for values of the curvaton-higgs coupling as large as 0.1. Our calculations also apply in the general case of curvaton decay into any non Standard Model species coupled to the thermal background.
We forecast the constraints on both Hu-Sawicki model and Bertschinger-Zukin model of modified gravity within the Parameterized Post-Friedmann (PPF) formalism for the Planck satellite experiment by performing the joint analysis of ISW-Lensing bispectrum and CMB power spectrum. We find that, even considering the temperature-temperature mode of CMB power spectrum only, Planck data are expected to reduce the error bars on the modified gravity parameter $B_0$ (related to the present value of Compton wavelength of the extra scalar degree of freedom) at least one order magnitude compared with WMAP. The spectrum-bispectrum joint analysis can further improve the results by a factor ranging from 1.14 to 5.32 depending on the specific modified gravity model. One of our main results is that the cross-correlation between ISW-Lensing bispectrum and power spectrum can be safely neglected when performing the joint analysis. For simplicity, we only investigate the likelihood of one parameter ({$B_0$}) and fix all other cosmological parameters to their best-fit values in WMAP7yr results.
We present projected constraints on the cosmic string tension, $G\mu/c^2$, that could be achieved by future gravitational wave detection experiments and express our results as semi-analytic relations of the form $G\mu(\Omega_{\rm gw}h^2)/c^2$, to allow for direct computation of the tension constraints for future experiments. These results can be applied to new constraints on $\Omega_{\rm gw}h^2$ as they are imposed. Experiments operating in different frequency bands probe different parts of the gravitational wave spectrum of a cosmic string network and are sensitive to different uncertainties in the underlying cosmic string model parameters. We compute the gravitational wave spectra of cosmic string networks based on the one-scale model, covering all the parameter space accessed by each experiment which is strongly dependent on the birth scale of loops relative to the horizon, $\alpha$. The upper limits on the string tension avoid any assumptions on the model parameters. We perform this investigation for Pulsar Timing Array experiments of different durations as well as ground-based and space-borne interferometric detectors.
Chemistry has a key role in the evolution of the interstellar medium (ISM), so it is highly desirable to follow its evolution in numerical simulations. However, it may easily dominate the computational cost when applied to large systems. In this paper we discuss two approaches to reduce these costs: (i) based on computational strategies, and (ii) based on the properties and on the topology of the chemical network. The first methods are more robust, while the second are meant to be giving important information on the structure of large, complex networks. To this aim we first discuss the numerical solvers for integrating the system of ordinary differential equations (ODE) associated with the chemical network. We then propose a buffer method that decreases the computational time spent in solving the ODE system. We further discuss a flux-based method that allows one to determine and then cut on the fly the less active reactions. In addition we also present a topological approach for selecting the most probable species that will be active during the chemical evolution, thus gaining information on the chemical network that otherwise would be difficult to retrieve. This topological technique can also be used as an a priori reduction method for any size network. We implemented these methods into a 1D Lagrangian hydrodynamical code to test their effects: both classes lead to large computational speed-ups, ranging from x2 to x5. We have also tested some hybrid approaches finding that coupling the flux method with a buffer strategy gives the best trade-off between robustness and speed-up of calculations.
We report on Herschel/PACS observations of absorption lines of OH+, H2O+ and H3O+ in NGC 4418 and Arp 220. Excited lines of OH+ and H2O+ with E_lower of at least 285 and \sim200 K, respectively, are detected in both sources, indicating radiative pumping and location in the high radiation density environment of the nuclear regions. Abundance ratios OH+/H2O+ of 1-2.5 are estimated in the nuclei of both sources. The inferred OH+ column and abundance relative to H nuclei are (0.5-1)x10^{16} cm-2 and \sim2x10^{-8}, respectively. Additionally, in Arp 220, an extended low excitation component around the nuclear region is found to have OH+/H2O+\sim5-10. H3O+ is detected in both sources with N(H3O+)\sim(0.5-2)x10^{16} cm-2, and in Arp 220 the pure inversion, metastable lines indicate a high rotational temperature of ~500 K, indicative of formation pumping and/or hot gas. Simple chemical models favor an ionization sequence dominated by H+ - O+ - OH+ - H2O+ - H3O+, and we also argue that the H+ production is most likely dominated by X-ray/cosmic ray ionization. The full set of observations and models leads us to propose that the molecular ions arise in a relatively low density (\gtrsim10^4 cm-3) interclump medium, in which case the ionization rate per H nucleus (including secondary ionizations) is zeta>10^{-13} s-1, a lower limit that is severalx10^2 times the highest rate estimates for Galactic regions. In Arp 220, our lower limit for zeta is compatible with estimates for the cosmic ray energy density inferred previously from the supernova rate and synchrotron radio emission, and also with the expected ionization rate produced by X-rays. In NGC 4418, we argue that X-ray ionization due to an AGN is responsible for the molecular ion production.
The expected gravitational wave (GW) signal due to double degenerates (DDs) in the thin Galactic disc is calculated using a Monte Carlo simulation. The number of young close DDs that will contribute observable discrete signals in the frequency range $1.58 - 15.8$ mHz is estimated by comparison with the sensitivity of proposed GW observatories. The present-day DD population is examined as a function of Galactic star-formation history alone. It is shown that the frequency distribution, in particular, is a sensitive function of the Galactic star formation history and could be used to measure the time since the last major star-formation epoch.
PoGOLite is a hard X-ray polarimeter operating in the 25-100 keV energy band. The instrument design is optimised for the observation of compact astrophysical sources. Observations are conducted from a stabilised stratospheric balloon platform at an altitude of approximately 40 km. The primary targets for first balloon flights of a reduced effective area instrument are the Crab and Cygnus-X1. The polarisation of incoming photons is determined using coincident Compton scattering and photo-absorption events reconstructed in an array of plastic scintillator detector cells surrounded by a bismuth germanate oxide (BGO) side anticoincidence shield and a polyethylene neutron shield. A custom attitude control system keeps the polarimeter field-of-view aligned to targets of interest, compensating for sidereal motion and perturbations such as torsional forces in the balloon rigging. An overview of the PoGOLite project is presented and the outcome of the ill-fated maiden balloon flight is discussed.
The CLEAN deconvolution algorithm has well-known limitations due to the restriction of locating point source model components on a discretized grid. In this letter we demonstrate that these limitations are even more pronounced when applying CLEAN in the case of Rotation Measure (RM) synthesis imaging. We suggest a modification that uses Maximum Likelihood estimation to adjust the CLEAN-derived sky model. We demonstrate through the use of mock one-dimensional RM synthesis observations that this technique shows significant improvement over standard CLEAN and gives results that are independent of the chosen image pixelization. We suggest using this simple modification to CLEAN in upcoming polarization sensitive sky surveys.
A hyperaccretion disk formed around a stellar mass black hole is a plausible model for the central engine that powers gamma-ray bursts (GRBs). If the central black hole rotates and a poloidal magnetic field threads its horizon, a powerful relativistic jet may be driven by a process resembling the Blandford-Znajek mechanism. We estimate the luminosity of such a jet assuming that the poloidal magnetic field strength is comparable to the inner accretion disk pressure. We show that the jet efficiency attains its maximal value when the accretion flow is cooled via optically-thin neutrino emission. The jet luminosity is much larger than the energy deposition through neutrino-antineutrino annihilation provided that the black hole is spinning rapidly enough. When the accretion rate onto a rapidly spinning black hole is large enough (> 0.003-0.01M_sun/sec), the predicted jet luminosity is sufficient to drive a GRB.
We analyze both the early and late time radio and X-ray data of the tidal disruption event Swift J1644+57. The data at early times ($\lesssim 5$ days) necessitates separation of the radio and X-ray emission regions, either spatially or in velocity space. This leads us to suggest a two component jet model, in which the inner jet is initially relativistic with Lorentz factor $\Gamma \approx 15$, while the outer jet is trans-relativistic, with $\Gamma \lesssim 1.2$. This model enables a self-consistent interpretation of the late time radio data, both in terms of peak frequency and flux. We solve the dynamics, radiative cooling and expected radiation from both jet components. We show that while during the first month synchrotron emission from the outer jet dominates the radio emission, at later times radiation from ambient gas collected by the inner jet dominates. This provides a natural explanation to the observed re-brightening, without the need for late time inner engine activity. After 100 days, the radio emission peak is in the optically thick regime, leading to a decay of both the flux and peak frequency at later times. Our model's predictions for the evolution of radio emission in jetted tidal disruption events can be tested by future observations.
We report a systematic and statistically significant offset between the optical (g-z or B-I) colors of seven massive elliptical galaxies and the mean colors of their associated massive metal-rich globular clusters (GCs) in the sense that the parent galaxies are redder by 0.12-0.20 mag at a given galactocentric distance. However, spectroscopic indices in the blue indicate that the luminosity-weighted ages and metallicities of such galaxies are equal to that of their averaged massive metal-rich GCs at a given galactocentric distance, to within small uncertainties. The observed color differences between the red GC systems and their parent galaxies cannot be explained by the presence of multiple stellar generations in massive metal-rich GCs, as the impact of the latter to the populations' integrated g-z or B-I colors is found to be negligible. However, we show that this paradox can be explained if the stellar initial mass function (IMF) in these massive elliptical galaxies was significantly steeper at subsolar masses than canonical IMFs derived from star counts in the solar neighborhood, with the GC colors having become bluer due to dynamical evolution, causing a significant flattening of the stellar MF of the average surviving GC.
We discuss the implications of purely classical, instead of quantum, theory of gravity for the gravitational wave spectrum generated during inflation. We show that a positive detection of primordial gravitational waves will no longer suffice to determine the scale of inflation in this case -- even a high-scale model of inflation can bypass the observational constraints due to large uncertainties in the initial classical amplitude of the tensor modes.
Remarkable observational advances have established a compelling
cross-validated model of the Universe. Yet, two key pillars of this model --
dark matter and dark energy -- remain mysterious. Sky surveys that map billions
of galaxies to explore the `Dark Universe', demand a corresponding
extreme-scale simulation capability; the HACC (Hybrid/Hardware Accelerated
Cosmology Code) framework has been designed to deliver this level of
performance now, and into the future. With its novel algorithmic structure,
HACC allows flexible tuning across diverse architectures, including accelerated
and multi-core systems.
On the IBM BG/Q, HACC attains unprecedented scalable performance -- currently
13.94 PFlops at 69.2% of peak and 90% parallel efficiency on 1,572,864 cores
with an equal number of MPI ranks, and a concurrency of 6.3 million. This level
of performance was achieved at extreme problem sizes, including a benchmark run
with more than 3.6 trillion particles, significantly larger than any
cosmological simulation yet performed.
Using a simplified model framework, we assess observational limits and discovery prospects for neutralino dark matter, taken here to be a general admixture of bino, wino, and Higgsino. Experimental constraints can be weakened or even nullified in regions of parameter space near 1) purity limits, where the dark matter is mostly bino, wino, or Higgsino, or 2) blind spots, where the relevant couplings of dark matter to the $Z$ or Higgs bosons vanish identically. We analytically identify all blind spots relevant to spin-independent and spin-dependent scattering and show that they arise for diverse choices of relative signs among $M_1$, $M_2$, and $\mu$. At present, XENON100 and IceCube still permit large swaths of viable parameter space, including the well-tempered neutralino. On the other hand, upcoming experiments should have sufficient reach to discover dark matter in much of the remaining parameter space. Our results are broadly applicable, and account for a variety of thermal and non-thermal cosmological histories, including scenarios in which neutralinos are just a component of the observed dark matter today. Because this analysis is indifferent to the fine-tuning of electroweak symmetry breaking, our findings also hold for many models of neutralino dark matter in the MSSM, NMSSM, and Split Supersymmetry. We have identified parameter regions at low $\tan \beta$ which sit in a double blind spot for both spin-independent and spin-dependent scattering. Interestingly, these low $\tan \beta$ regions are independently favored in the NMSSM and models of Split Supersymmetry which accommodate a Higgs mass near 125 GeV.
We evaluate the effective mass of a scalar field phi coupled to thermal plasma through Planck-suppressed interactions. We find it useful to rescale the coupled fields so that all the phi-dependences are absorbed into the yukawa and gauge couplings, which allows us to read off the leading order contributions to the effective mass \tilde m_{phi} from the 2-loop free energy calculated with the rescaled couplings. We give an analytical expression for \tilde m_{phi} at a sufficiently high temperature in the case where phi is coupled to the MSSM chiral superfields through non-minimal Kahler potential. We find that \tilde m_{phi}^2 is about 10^{-3} H^2 \sim 10^{-2} H^2 for typical parameter sets, where H is the Hubble expansion rate in the radiation-dominated era.
It is shown that F(R)-modified gravitational theories lead to curvature oscillations in astrophysical systems with rising energy density. The frequency and the amplitude of such oscillations could be very high and would lead to noticeable production of energetic cosmic ray particles.
A general nonperturvative loop quantization procedure for metric modified gravity is reviewed. As an example, this procedure is applied to scalar-tensor theories of gravity. The quantum kinematical framework of these theories is rigorously constructed. Both the Hamiltonian and master constraint operators are well defined and proposed to represent quantum dynamics of scalar-tensor theories. As an application to models, we set up the basic structure of loop quantum Brans-Dicke cosmology. The effective dynamical equations of loop quantum Brans-Dicke cosmology are also obtained, which lay a foundation for the phenomenological investigation to possible quantum gravity effects in cosmology.
The complementarity between dark matter searches at colliders and in underground laboratories is an extraordinarily powerful tool in the quest for dark matter. In the vast majority of the analyses conducted so far these dark matter detection strategies have been profitably combined either to perform global fits in the context of certain particle physics models (e.g. the CMSSM) or to estimate the prospects for a direct dark matter detection given the LHC potential of discovering new physics beyond the Standard Model. In this paper we propose an alternative strategy to combine direct and collider dark matter searches: employing the potential of the upcoming generation of 1-ton direct detection experiments, we show that for certain supersymmetric configurations it is possible to translate the information encoded in an hypothetically discovered direct detection signal into classes of expected signals at the LHC. As an illustrative application of our method, we show that for a 60 GeV neutralino thermally produced via resonant annihilations and identified by a 1-ton direct detection experiment, our approach allows to forecast a clearly identifiable prediction for a LHC final state involving three leptons and missing energy. The strategy presented in this paper to systematically translate a direct detection signal into a prediction for the LHC has the potential to significantly strengthen the complementarity between these two dark matter detection strategies.
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Broad absorption lines (BALs) in quasar spectra are prominent signatures of high-velocity outflows, which might be present in all quasars and could be a major contributor to feedback to galaxy evolution. Studying the variability in these BALs allows us to further our understanding of the structure, evolution, and basic physical properties of the outflows. This is the third paper in a series on a monitoring programme of 24 luminous BAL quasars at redshifts 1.2 < z < 2.9. We focus here on the time-scales of variability in CIV 1549A BALs in our full multi-epoch sample, which covers time-scales from 0.02-8.7 yr in the quasar rest-frame. Our sample contains up to 13 epochs of data per quasar, with an average of 7 epochs per quasar. We find that both the incidence and the amplitude of variability are greater across longer time-scales. Part of our monitoring programme specifically targeted half of these BAL quasars at rest-frame time-scales <2 months. This revealed variability down to the shortest time-scales we probe (8-10 days). Observed variations in only portions of BAL troughs or in lines that are optically thick suggest that at least some of these changes are caused by clouds (or some type of outflow substructures) moving across our lines of sight. In this crossing cloud scenario, the variability times constrain both the crossing speeds and the absorber locations. Typical variability times of order ~1 year indicate crossing speeds of a few thousand km/s and radial distances near ~1 pc from the central black hole. However, the most rapid BAL changes occurring in 8-10 days require crossing speeds of 17 000 - 84 000 km/s and radial distances of only 0.001-0.02 pc. These speeds are similar to or greater than the observed radial outflow speeds, and the inferred locations are within the nominal radius of the broad emission line region.
We present IRIS, a new generic three-dimensional (3D) spectral radiative transfer code that generates synthetic spectra, or images. It can be used as a diagnostic tool for comparison with astrophysical observations or laboratory astrophysics experiments. We have developed a 3D short-characteristic solver that works with a 3D nonuniform Cartesian grid. We have implemented a piecewise cubic, locally monotonic, interpolation technique that dramatically reduces the numerical diffusion effect. The code takes into account the velocity gradient effect resulting in gradual Doppler shifts of photon frequencies and subsequent alterations of spectral line profiles. It can also handle periodic boundary conditions. This first version of the code assumes Local Thermodynamic Equilibrium (LTE) and no scattering. The opacities and source functions are specified by the user. In the near future, the capabilities of IRIS will be extended to allow for non-LTE and scattering modeling. IRIS has been validated through a number of tests. We provide the results for the most relevant ones, in particular a searchlight beam test, a comparison with a 1D plane-parallel model, and a test of the velocity gradient effect. IRIS is a generic code to address a wide variety of astrophysical issues applied to different objects or structures, such as accretion shocks, jets in young stellar objects, stellar atmospheres, exoplanet atmospheres, accretion disks, rotating stellar winds, cosmological structures. It can also be applied to model laboratory astrophysics experiments, such as radiative shocks produced with high power lasers.
Massive black holes in galactic nuclei vary their mass M and spin vector J due to accretion. In this study we relax, for the first time, the assumption that accretion can be either chaotic, i.e. when the accretion episodes are randomly and isotropically oriented, or coherent, i.e. when they occur all in a preferred plane. Instead, we consider different degrees of anisotropy in the fueling, never confining to accretion events on a fixed direction. We follow the black hole growth evolving contemporarily mass, spin modulus a and spin direction. We discover the occurrence of two regimes. An early phase (M <~ 10 million solar masses) in which rapid alignment of the black hole spin direction to the disk angular momentum in each single episode leads to erratic changes in the black hole spin orientation and at the same time to large spins (a ~ 0.8). A second phase starts when the black hole mass increases above >~ 10 million solar masses and the accretion disks carry less mass and angular momentum relatively to the hole. In the absence of a preferential direction the black holes tend to spin-down in this phase. However, when a modest degree of anisotropy in the fueling process (still far from being coherent) is present, the black hole spin can increase up to a ~ 1 for very massive black holes (M >~ 100 million solar masses), and its direction is stable over the many accretion cycles. We discuss the implications that our results have in the realm of the observations of black hole spin and jet orientations.
Sloshing cold fronts (CFs) arise from minor merger triggered gas sloshing. Their detailed structure depends on the properties of the intra-cluster medium (ICM): hydrodynamical simulations predict the CFs to be distorted by Kelvin-Helmholtz instabilities (KHIs), but aligned magnetic fields, viscosity, or thermal conduction can suppress the KHIs. Thus, observing the detailed structure of sloshing CFs can be used to constrain these ICM properties. Both smooth and distorted sloshing CFs have been observed, indicating that the KHI is suppressed in some clusters, but not in all. Consequently, we need to address at least some sloshing clusters individually before drawing general conclusions about the ICM properties. We present the first detailed attempt to constrain the ICM properties in a specific cluster from the structure of its sloshing CF. Proximity and brightness make the Virgo cluster an ideal target. We combine observations and Virgo-specific hydrodynamical sloshing simulations. Here we focus on a Spitzer-like temperature dependent viscosity as a mechanism to suppress the KHI, but discuss the alternative mechanisms in detail. We identify the CF at 90 kpc north and north-east of the Virgo center as the best location in the cluster to observe a possible KHI suppression. For viscosities $\gtrsim$ 10% of the Spitzer value KHIs at this CF are suppressed. We describe in detail the observable signatures at low and high viscosities, i.e. in the presence or absence of KHIs. We find indications for a low ICM viscosity in archival XMM-Newton data and demonstrate the detectability of the predicted features in deep Chandra observations.
The evolution of small systems such as dwarf spheroidal galaxies (dSph) is
likely to have been a balance between external environmental effects and
internal processes within their own relatively shallow potential wells.
Assessing how strong such environmental interactions may have been is therefore
an important element in understanding the baryonic evolution of dSphs and their
derived dark matter distribution.
Here we present results from a wide-area CTIO/MOSAIC II photometric survey of
the Carina dSph, reaching down to about two magnitudes below the oldest main
sequence turn-off (MSTO). This data-set enables us to trace the structure of
Carina in detail out to very large distances from its center, and as a function
of stellar age.
We observe the presence of an extended structure made up primarily of ancient
MSTO stars, at distances between 25arcmin-60arcmin from Carina's center,
confirming results in the literature that Carina extends well beyond its
nominal tidal radius.
The large number statistics of our survey reveals features such as isophote
twists and tails that had gone undetected in other previous shallower surveys.
This is the first time that such unambiguous signs of tidal disruption have
been found in a Milky Way "classical" dwarf other than Sagittarius.
We also demonstrate the presence of a negative age gradient in Carina
directly from its MSTOs, and trace it out to very large distances from the
galaxy center. The signs of interaction with the Milky Way make it unclear
whether the age gradient was already in place before Carina underwent tidal
disruption.
In a previous paper we presented the Directed Follow-Up (DFU) approach, which we suggested can be used to efficiently augment low-cadence photometric surveys in a way that will optimize the chances to detect transiting exoplanets. In this paper we present preliminary tests of applying the DFU approach to the future ESA space mission Gaia. We demonstrate the strategy application to Gaia photometry through a few simulated cases of known transiting planets, using Gaia expected performance and current design. We show that despite the low cadence observations DFU, when tailored for Gaia's scanning law, can facilitate detection of transiting planets with ground-based observations, even during the lifetime of the mission. We conclude that Gaia photometry, although not optimized for transit detection, should not be ignored in the search of transiting planets. With a suitable ground-based follow-up network it can make an important contribution to this search.
We observed nine primary transits of the hot Jupiter TrES-3b in several optical and near-UV photometric bands from 2009 June to 2012 April in an attempt to detect its magnetic field. Vidotto, Jardine and Helling suggest that the magnetic field of TrES-3b can be constrained if its near-UV light curve shows an early ingress compared to its optical light curve, while its egress remains unaffected. Predicted magnetic field strengths of Jupiter-like planets should range between 8 G and 30 G. Using these magnetic field values and an assumed B_star of 100 G, the Vidotto et al. method predicts a timing difference of 5-11 min. We did not detect an early ingress in our three nights of near-UV observations, despite an average cadence of 68 s and an average photometric precision of 3.7 mmag. However, we determined an upper limit of TrES-3b's magnetic field strength to range between 0.013 and 1.3 G (for a 1-100 G magnetic field strength range for the host star, TrES-3) using a timing difference of 138 s derived from the Nyquist-Shannon sampling theorem. To verify our results of an abnormally small magnetic field strength for TrES-3b and to further constrain the techniques of Vidotto et al., we propose future observations of TrES-3b with other platforms capable of achieving a shorter near-UV cadence. We also present a refinement of the physical parameters of TrES-3b, an updated ephemeris and its first published near-UV light curve. We find that the near-UV planetary radius of Rp = 1.386+0.248-0.144 RJup is consistent with the planet's optical radius.
We present a high-performance, graphics processing unit (GPU)-based framework for the efficient analysis and visualization of (nearly) terabyte (TB)-sized 3-dimensional images. Using a cluster of 96 GPUs, we demonstrate for a 0.5 TB image: (1) volume rendering using an arbitrary transfer function at 7--10 frames per second; (2) computation of basic global image statistics such as the mean intensity and standard deviation in 1.7 s; (3) evaluation of the image histogram in 4 s; and (4) evaluation of the global image median intensity in just 45 s. Our measured results correspond to a raw computational throughput approaching one teravoxel per second, and are 10--100 times faster than the best possible performance with traditional single-node, multi-core CPU implementations. A scalability analysis shows the framework will scale well to images sized 1 TB and beyond. Other parallel data analysis algorithms can be added to the framework with relative ease, and accordingly, we present our framework as a possible solution to the image analysis and visualization requirements of next-generation telescopes, including the forthcoming Square Kilometre Array pathfinder radiotelescopes.
Debris disks have been found primarily around intermediate and solar mass stars (spectral types A-K) but rarely around low mass M-type stars. We have spatially resolved a debris disk around the remarkable M3-type star GJ581 hosting multiple planets using deep PACS images at 70, 100 and 160 microns as part of the DEBRIS Program on the Herschel Space Observatory. This is the second spatially resolved debris disk found around an M-type star, after the one surrounding the young star AU Mic (12 Myr). However, GJ 581 is much older (2-8 Gyr), and is X-ray quiet in the ROSAT data. We fit an axisymmetric model of the disk to the three PACS images and found that the best fit model is for a disk extending radially from 25+/-12 AU to more than 60 AU. Such a cold disk is reminiscent of the Kuiper Belt but it surrounds a low mass star (0.3 M_sol) and its fractional dust luminosity L_dust/L_* of \sim 10^-4 is much higher. The inclination limits of the disk found in our analysis make the masses of the planets small enough to ensure the long-term stability of the system according to some dynamical simulations. The disk is collisionally dominated down to submicron-sized grains and the dust cannot be expelled from the system by radiation or wind pressures because of the low luminosity and low X-ray luminosity of GJ581. We suggest that the correlation between low-mass planets and debris disks recently found for G-type stars also applies to M-type stars.Finally, the known planets, of low masses and orbiting within 0.3 AU from the star, cannot dynamically perturb the disk over the age of the star, suggesting that an additional planet exists at larger distance that is stirring the disk to replenish the dust.
Different formulations of MOND predict somewhat different rotation curves for the same mass distribution. Here I consider a global attribute of the rotation curve that might provide a convenient discriminant between theories when applied to isolated, pure-disk galaxies that are everywhere deep in the MOND regime. This parameter is Q=<V^2>/V0^2, where <V^2> is the mean squared rotational speed of the galaxy, and V0 is the asymptotic (constant) rotational speed. The comparison between the observed and predicted values of Q is oblivious to the distance, the inclination, the mass, and the size of the disk, and to the form of the interpolating function. For the known modified-gravity theories Q is predicted to be a universal constant (independent of the mass distribution in the disk): Q=2/3. The predicted Q value for modified-inertia theories does depend on the mass distribution. However, surprisingly, I find here that it varies only little among a very wide range of mass distributions, Q=0.73+-0.01. While the difference between the theories amounts to only about 5 percent in the predicted RMS velocity, a good enough sample of galaxies may provide the first discerning test between the two classes of theories.
A thorough search of the sky exposed at the Pierre Auger Cosmic Ray Observatory reveals no statistically significant excess of events in any small solid angle that would be indicative of a flux of neutral particles from a discrete source. The search covers from -90 to +15 degrees in declination using four different energy ranges above 1 EeV (10^18 eV). The method used in this search is more sensitive to neutrons than to photons. The upper limit on a neutron flux is derived for a dense grid of directions for each of the four energy ranges. These results constrain scenarios for the production of ultra-high energy cosmic rays in the Galaxy.
This paper provides a framework for incorporation of the wavefront sensor
sensor measurements in the context of observing modes in which the science
camera takes very short exposures. In this formulation, the wavefront sensor
measurements provide a means to jointly the static speckle and the planetary
signal. For simplicity, the mathematical development assumes a simple optical
system with an idealized Lyot coronagraph. Unlike currently used methods, in
which increasing the observation time beyond a certain threshold is useless,
this method produces estimates whose error covariances are inversely
proportional to the observation time due to the fact that the (quasi-)static
speckle and planetary emission are jointly estimated. The method can easily be
extended to include angular (due to diurnal field rotation) and spectral
diversity.
Numerical experiments are performed with wavefront data from the AEOS
Adaptive Optics System sensing at 850 nm. These experiments assume a science
camera wavelength of $2.2 \mu$, that the measured wavefronts are exact, an
ideal coronagraph, and a Gaussian approximation of shot-noise. A number of
static aberrations are introduced, including one with a spatial frequency
exactly corresponding the planet location. Using only 4 seconds of observation
time, a planetary intensity of $\sim 0.2$ photons/millisecond, a stellar
intensity of $\sim 9$ photons/millisecond/pixel at the planet's location, the
short-exposure estimation method recovers the correct amplitudes of all static
aberrations as well the correct planet brightness with a contrast ratio of
$10^{-6}$ with 17% accuracy. The ideal coronagraph itself provides about 95%
extinction in the frames with the highest Strehl ratios.
The lowest frequency band (70 - 450 MHz) of the Square Kilometre Array will consist of sparse aperture arrays grouped into geographically-localised patches, or stations. Signals from thousands of antennas in each station will be beamformed to produce station beams which form the inputs for the central correlator. Two-stage beamforming within stations can reduce SKA-low signal processing load and costs, but has not been previously explored for the irregular station layouts now favoured in radio astronomy arrays. This paper illustrates the effects of two-stage beamforming on sidelobes and effective area, for two representative station layouts (regular and irregular gridded tile on an irregular station). The performance is compared with a single-stage, irregular station. The inner sidelobe levels do not change significantly between layouts, but the more distant sidelobes are affected by the tile layouts; regular tile creates diffuse, but regular, grating lobes. With very sparse arrays, the station effective area is similar between layouts. At lower frequencies, the regular tile significantly reduces effective area, hence sensitivity. The effective area is highest for a two-stage irregular station, but it requires a larger station extent than the other two layouts. Although there are cost benefits for stations with two-stage beamforming, we conclude that more accurate station modelling, and SKA-low configuration specifications, are required before design finalisation.
Effects of light millicharged dark matter particles on primordial nucleosynthesis are considered. It is shown that if the mass of such particles is much smaller than the electron mass, they lead to strong overproduction of Helium-4. An agreement with observations can be achieved by non-vanishing lepton asymmetry. Baryon-to-photon ratio at BBN and neutrino-to-photon ratio both at BBN and at recombination are noticeably different as compared to the standard cosmological model. The latter ratio and possible lepton asymmetry could be checked by Planck. For higher mass of new particles the effect is much less pronounced and may even have opposite sign.
Turbulence is thought to be a key driver of the evolution of protoplanetary
disks, regulating the mass accretion process, the transport of angular
momentum, and the growth of dust particles.
We intend to determine the magnitude of the turbulent motions in the outer
parts (> 100 AU) of the disk surrounding DM Tau. Turbulent motions can be
constrained by measuring the nonthermal broadening of line emission from heavy
molecules. We used the IRAM Plateau de Bure interferometer to study emission
from the CS molecule in the disk of DM Tau. High spatial (1.4 x 1 ") and
spectral resolution (0.126 km/s) CS J=3-2 images provide constraints on the
molecule distribution and velocity structure of the disk. A low sensitivity CS
J=5-4 image was used in conjunction to evaluate the excitation conditions. We
analyzed the data in terms of two parametric disk models, and compared the
results with detailed time-dependent chemical simulations.
The CS data confirm the relatively low temperature suggested by observations
of other simple molecules. The intrinsic linewidth derived from the CS J=3-2
data is much larger than expected from pure thermal broadening. The magnitude
of the derived nonthermal component depends only weakly on assumptions about
the location of the CS molecules with respect to the disk plane. Our results
indicate turbulence with a Mach number around 0.4 - 0.5 in the molecular layer.
Geometrical constraints suggest that this layer is located near one scale
height, in reasonable agreement with chemical model predictions.
Asymptotic giant branch (AGB) stars with low initial mass (1 - 3 Msun) are responsible for the production of neutron-capture elements through the main s-process (main slow neutron capture process). The major neutron source is 13C(alpha, n)16O, which burns radiatively during the interpulse periods at about 8 keV and produces a rather low neutron density (10^7 n/cm^3). The second neutron source 22Ne(alpha, n)25Mg, partially activated during the convective thermal pulses when the energy reaches about 23 keV, gives rise to a small neutron exposure but a peaked neutron density (Nn(peak) > 10^11 n/cm^3). At metallicities close to solar, it does not substantially change the final s-process abundances, but mainly affects the isotopic ratios near s-path branchings sensitive to the neutron density. We examine the effect of the present uncertainties of the two neutron sources operating in AGB stars, as well as the competition with the 22Ne(alpha, gamma)26Mg reaction. The analysis is carried out on AGB the main-s process component (reproduced by an average between M(AGB; ini) = 1.5 and 3 Msun at half solar metallicity, see Arlandini et al. 1999), using a set of updated nucleosynthesis models. Major effects are seen close to the branching points. In particular, 13C(alpha, n)16O mainly affects 86Kr and 87Rb owing to the branching at 85Kr, while small variations are shown for heavy isotopes by decreasing or increasing our adopted rate by a factor of 2 - 3. By changing our 22Ne(alpha, n)25Mg rate within a factor of 2, a plausible reproduction of solar s-only isotopes is still obtained. We provide a general overview of the major consequences of these variations on the s-path. A complete description of each branching will be presented in Bisterzo et al., in preparation.
We present the status of LAUE, a project supported by the Italian Space Agency (ASI), and devoted to develop Laue lenses with long focal length (up to 100 meters), for hard X--/soft gamma--ray astronomy (80-600 keV). Thanks to their focusing capability, the design goal is to improve the sensitivity of the current instrumention in the above energy band by 2 orders of magnitude, down to a few times $10^{-8}$ photons/(cm$^2$ s keV).
The first stars are the key to the formation of primitive galaxies, early cosmological reionization and chemical enrichment, and the origin of supermassive black holes. Unfortunately, in spite of their extreme luminosities, individual Population III stars will likely remain beyond the reach of direct observation for decades to come. However, their properties could be revealed by their supernova explosions, which may soon be detected by a new generation of NIR observatories such as JWST and WFIRST. We present light curves and spectra for Pop III pair-instability supernovae calculated with the Los Alamos radiation hydrodynamics code RAGE. Our numerical simulations account for the interaction of the blast with realistic circumstellar envelopes, the opacity of the envelope, and Lyman absorption by the neutral IGM at high redshift, all of which are crucial to computing the NIR signatures of the first cosmic explosions. We find that JWST will detect pair-instability supernovae out to z > 30, WFIRST will detect them in all-sky surveys out to z ~ 15 - 20 and LSST and Pan-STARRS will find them at z ~ 7 - 8. The discovery of these ancient explosions will probe the first stellar populations and reveal the existence of primitive galaxies that might not otherwise have been detected.
Molecular hydrogen is the most abundant molecule in the universe. A large fraction of H2 forms by association of hydrogen atoms adsorbed on polycyclic aromatic hydrocarbons (PAHs), where formation rates depend crucially on the H sticking probability. We have experimentally studied PAH hydrogenation by exposing coronene cations, confined in a radiofrequency ion trap, to gas phase atomic hydrogen. A systematic increase of the number of H atoms adsorbed on the coronene with the time of exposure is observed. Odd coronene hydrogenation states dominate the mass spectrum up to 11 H atoms attached. This indicates the presence of a barrier preventing H attachment to these molecular systems. For the second and fourth hydrogenation, barrier heights of 72 +- 6 meV and 40 +- 10 meV, respectively are found which is in good agreement with theoretical predictions for the hydrogenation of neutral PAHs. Our experiments however prove that the barrier does not vanish for higher hydrogenation states. These results imply that PAH cations, as their neutral counterparts, exist in highly hydrogenated forms in the interstellar medium. Due to this catalytic activity, PAH cations and neutrals seem to contribute similarly to the formation of H2.
We report about new episode of decretion disk formation in the IGR J06074+2205 system. Obtained spectral data gives us opportunity to measure peak separation in double-peaked H\alpha\ line as 408+/-55 km/s and hence obtain disk radii as 1.6 star radii. All these facts may says about possible X-ray activity of IGR J06074+2205 in the nearest future.
In the context of the LAUE project devoted to build a long focal length focusing optics for soft gamma-ray astronomy (70/100 keV to $>$600 keV), we present results of simulation of a Laue lens, based on bent crystals in different assembling configurations (quasi-mosaic and reflection-like geometries). The main aim is to significantly overcome the sensitivity limits of the current generation of gamma-ray telescopes and improve the imaging capability.
We have recently developed a coupled chemistry-emission model for the green and red-doublet emissions of atomic oxygen on comet Hyakutake. In the present work we applied our model to comet Hale-Bopp, which had an order of magnitude higher H2O production rate than comet Hyakutake, to evaluate the photochemistry associated with the production and loss of O(1S) and O(1D) atoms and emission processes of green and red-doublet lines. We present the wavelength-dependent photo-attenuation rates for different photodissociation processes forming O(1S) and O(1D). The calculated radiative efficiency profiles of O(1S) and O(1D) atoms show that in comet Hale-Bopp the green and red-doublet emissions are emitted mostly above radial distances of 10^3 and 10^4 km, respectively. The model calculated [OI] 6300 A emission surface brightness and average intensity over the Fabry-P{\'e}rot spectrometer field of view are consistent with the observation of Morgenthaler et al. (2001), while the intensity ratio of green to red-doublet emission is in agreement with the observation of Zhang et al. (2001). In comet Hale-Bopp, for cometocentric distances less than 10^5 km, the intensity of [OI] 6300 A line is mainly governed by photodissociation of H2O. Beyond 10^5 km, O(1D) production is dominated by photodissociation of the water photochemical daughter product OH. Whereas the [OI] 5577 A emission line is controlled by photodissociation of both H2O and CO2. The calculated mean excess energy in various photodissociation processes show that the photodissociation of CO2 can produce O(1S) atoms with higher excess velocity compared to the photodissociation of H2O. Thus, our model calculations suggest that involvement of multiple sources in the formation of O(1S) could be a reason for the larger width of green line than that of red-doublet emission lines observed in several comets.
In the context of the LAUE project devoted to build a long focal-length focusing optics for soft $\gamma$-ray astronomy (80 - 600 keV), we present the results of reflectivity measurements of bent crystals in different configurations, obtained by bending perfect or mosaic flat crystals. We also compare these results with those obtained using flat crystals. The measurements were performed using the K$\alpha$ line of the Tungsten anode of the X-ray tube used in the LARIX facility of the University of Ferrara. These results are finalized to select the best materials and to optimize the thickness of the crystal tiles that will be used for building a Laue lens petal which is a part of an entire Laue lens, with 20 m focal length and 100-300 keV passband. The final goal of the LAUE project is overcome, by at least 2 orders of magnitude, the sensitivity limits of the current generation of $\gamma$-ray telescopes, and to improve the current $\gamma$-ray imaging capability.
The spatial variation of the colour of a galaxy may introduce a bias in the
measurement of its shape if the PSF profile depends on wavelength. We study how
this bias depends on the properties of the PSF and the galaxies themselves. The
bias depends on the scales used to estimate the shape, which may be used to
optimise methods to reduce the bias. Here we develop a general approach to
quantify the bias. Although applicable to any weak lensing survey, we focus on
the implications for the ESA Euclid mission.
Based on our study of synthetic galaxies we find that the bias is a few times
10^-3 for a typical galaxy observed by Euclid. Consequently, it cannot be
neglected and needs to be accounted for. We demonstrate how one can do so using
spatially resolved observations of galaxies in two filters. We show that HST
observations in the F606W and F814W filters allow us to model and reduce the
bias by an order of magnitude, sufficient to meet Euclid's scientific
requirements. The precision of the correction is ultimately determined by the
number of galaxies for which spatially-resolved observations in at least two
filters are available. We use results from the Millennium Simulation to
demonstrate that archival HST data will be sufficient for the tomographic
cosmic shear analysis with the Euclid dataset.
We investigate in detail a model where the curvaton is coupled to the Standard Model higgs. Parametric resonance might be expected to cause a fast decay of the curvaton, so that it would not have time to build up the curvature perturbation. However, we show that this is not the case, and that the resonant decay of the curvaton may be delayed even down to electroweak symmetry breaking. This delay is due to the coupling of the higgs to the thermal background, which is formed by the Standard Model degrees of freedom created from the inflaton decay. We establish the occurrence of the delay by considering the curvaton evolution and the structure of the higgs resonances. We then provide analytical expressions for the delay time, and for the subsequent resonant production of the higgs, which ultimately leads to the curvaton effective decay width. Contrary to expectations, it is possible to obtain the observed curvature perturbation for values of the curvaton-higgs coupling as large as 0.1. Our calculations also apply in the general case of curvaton decay into any non Standard Model species coupled to the thermal background.
We forecast the constraints on both Hu-Sawicki model and Bertschinger-Zukin model of modified gravity within the Parameterized Post-Friedmann (PPF) formalism for the Planck satellite experiment by performing the joint analysis of ISW-Lensing bispectrum and CMB power spectrum. We find that, even considering the temperature-temperature mode of CMB power spectrum only, Planck data are expected to reduce the error bars on the modified gravity parameter $B_0$ (related to the present value of Compton wavelength of the extra scalar degree of freedom) at least one order magnitude compared with WMAP. The spectrum-bispectrum joint analysis can further improve the results by a factor ranging from 1.14 to 5.32 depending on the specific modified gravity model. One of our main results is that the cross-correlation between ISW-Lensing bispectrum and power spectrum can be safely neglected when performing the joint analysis. For simplicity, we only investigate the likelihood of one parameter ({$B_0$}) and fix all other cosmological parameters to their best-fit values in WMAP7yr results.
We present projected constraints on the cosmic string tension, $G\mu/c^2$, that could be achieved by future gravitational wave detection experiments and express our results as semi-analytic relations of the form $G\mu(\Omega_{\rm gw}h^2)/c^2$, to allow for direct computation of the tension constraints for future experiments. These results can be applied to new constraints on $\Omega_{\rm gw}h^2$ as they are imposed. Experiments operating in different frequency bands probe different parts of the gravitational wave spectrum of a cosmic string network and are sensitive to different uncertainties in the underlying cosmic string model parameters. We compute the gravitational wave spectra of cosmic string networks based on the one-scale model, covering all the parameter space accessed by each experiment which is strongly dependent on the birth scale of loops relative to the horizon, $\alpha$. The upper limits on the string tension avoid any assumptions on the model parameters. We perform this investigation for Pulsar Timing Array experiments of different durations as well as ground-based and space-borne interferometric detectors.
Chemistry has a key role in the evolution of the interstellar medium (ISM), so it is highly desirable to follow its evolution in numerical simulations. However, it may easily dominate the computational cost when applied to large systems. In this paper we discuss two approaches to reduce these costs: (i) based on computational strategies, and (ii) based on the properties and on the topology of the chemical network. The first methods are more robust, while the second are meant to be giving important information on the structure of large, complex networks. To this aim we first discuss the numerical solvers for integrating the system of ordinary differential equations (ODE) associated with the chemical network. We then propose a buffer method that decreases the computational time spent in solving the ODE system. We further discuss a flux-based method that allows one to determine and then cut on the fly the less active reactions. In addition we also present a topological approach for selecting the most probable species that will be active during the chemical evolution, thus gaining information on the chemical network that otherwise would be difficult to retrieve. This topological technique can also be used as an a priori reduction method for any size network. We implemented these methods into a 1D Lagrangian hydrodynamical code to test their effects: both classes lead to large computational speed-ups, ranging from x2 to x5. We have also tested some hybrid approaches finding that coupling the flux method with a buffer strategy gives the best trade-off between robustness and speed-up of calculations.
We report on Herschel/PACS observations of absorption lines of OH+, H2O+ and H3O+ in NGC 4418 and Arp 220. Excited lines of OH+ and H2O+ with E_lower of at least 285 and \sim200 K, respectively, are detected in both sources, indicating radiative pumping and location in the high radiation density environment of the nuclear regions. Abundance ratios OH+/H2O+ of 1-2.5 are estimated in the nuclei of both sources. The inferred OH+ column and abundance relative to H nuclei are (0.5-1)x10^{16} cm-2 and \sim2x10^{-8}, respectively. Additionally, in Arp 220, an extended low excitation component around the nuclear region is found to have OH+/H2O+\sim5-10. H3O+ is detected in both sources with N(H3O+)\sim(0.5-2)x10^{16} cm-2, and in Arp 220 the pure inversion, metastable lines indicate a high rotational temperature of ~500 K, indicative of formation pumping and/or hot gas. Simple chemical models favor an ionization sequence dominated by H+ - O+ - OH+ - H2O+ - H3O+, and we also argue that the H+ production is most likely dominated by X-ray/cosmic ray ionization. The full set of observations and models leads us to propose that the molecular ions arise in a relatively low density (\gtrsim10^4 cm-3) interclump medium, in which case the ionization rate per H nucleus (including secondary ionizations) is zeta>10^{-13} s-1, a lower limit that is severalx10^2 times the highest rate estimates for Galactic regions. In Arp 220, our lower limit for zeta is compatible with estimates for the cosmic ray energy density inferred previously from the supernova rate and synchrotron radio emission, and also with the expected ionization rate produced by X-rays. In NGC 4418, we argue that X-ray ionization due to an AGN is responsible for the molecular ion production.
The expected gravitational wave (GW) signal due to double degenerates (DDs) in the thin Galactic disc is calculated using a Monte Carlo simulation. The number of young close DDs that will contribute observable discrete signals in the frequency range $1.58 - 15.8$ mHz is estimated by comparison with the sensitivity of proposed GW observatories. The present-day DD population is examined as a function of Galactic star-formation history alone. It is shown that the frequency distribution, in particular, is a sensitive function of the Galactic star formation history and could be used to measure the time since the last major star-formation epoch.
PoGOLite is a hard X-ray polarimeter operating in the 25-100 keV energy band. The instrument design is optimised for the observation of compact astrophysical sources. Observations are conducted from a stabilised stratospheric balloon platform at an altitude of approximately 40 km. The primary targets for first balloon flights of a reduced effective area instrument are the Crab and Cygnus-X1. The polarisation of incoming photons is determined using coincident Compton scattering and photo-absorption events reconstructed in an array of plastic scintillator detector cells surrounded by a bismuth germanate oxide (BGO) side anticoincidence shield and a polyethylene neutron shield. A custom attitude control system keeps the polarimeter field-of-view aligned to targets of interest, compensating for sidereal motion and perturbations such as torsional forces in the balloon rigging. An overview of the PoGOLite project is presented and the outcome of the ill-fated maiden balloon flight is discussed.
The CLEAN deconvolution algorithm has well-known limitations due to the restriction of locating point source model components on a discretized grid. In this letter we demonstrate that these limitations are even more pronounced when applying CLEAN in the case of Rotation Measure (RM) synthesis imaging. We suggest a modification that uses Maximum Likelihood estimation to adjust the CLEAN-derived sky model. We demonstrate through the use of mock one-dimensional RM synthesis observations that this technique shows significant improvement over standard CLEAN and gives results that are independent of the chosen image pixelization. We suggest using this simple modification to CLEAN in upcoming polarization sensitive sky surveys.
A hyperaccretion disk formed around a stellar mass black hole is a plausible model for the central engine that powers gamma-ray bursts (GRBs). If the central black hole rotates and a poloidal magnetic field threads its horizon, a powerful relativistic jet may be driven by a process resembling the Blandford-Znajek mechanism. We estimate the luminosity of such a jet assuming that the poloidal magnetic field strength is comparable to the inner accretion disk pressure. We show that the jet efficiency attains its maximal value when the accretion flow is cooled via optically-thin neutrino emission. The jet luminosity is much larger than the energy deposition through neutrino-antineutrino annihilation provided that the black hole is spinning rapidly enough. When the accretion rate onto a rapidly spinning black hole is large enough (> 0.003-0.01M_sun/sec), the predicted jet luminosity is sufficient to drive a GRB.
We analyze both the early and late time radio and X-ray data of the tidal disruption event Swift J1644+57. The data at early times ($\lesssim 5$ days) necessitates separation of the radio and X-ray emission regions, either spatially or in velocity space. This leads us to suggest a two component jet model, in which the inner jet is initially relativistic with Lorentz factor $\Gamma \approx 15$, while the outer jet is trans-relativistic, with $\Gamma \lesssim 1.2$. This model enables a self-consistent interpretation of the late time radio data, both in terms of peak frequency and flux. We solve the dynamics, radiative cooling and expected radiation from both jet components. We show that while during the first month synchrotron emission from the outer jet dominates the radio emission, at later times radiation from ambient gas collected by the inner jet dominates. This provides a natural explanation to the observed re-brightening, without the need for late time inner engine activity. After 100 days, the radio emission peak is in the optically thick regime, leading to a decay of both the flux and peak frequency at later times. Our model's predictions for the evolution of radio emission in jetted tidal disruption events can be tested by future observations.
We report a systematic and statistically significant offset between the optical (g-z or B-I) colors of seven massive elliptical galaxies and the mean colors of their associated massive metal-rich globular clusters (GCs) in the sense that the parent galaxies are redder by 0.12-0.20 mag at a given galactocentric distance. However, spectroscopic indices in the blue indicate that the luminosity-weighted ages and metallicities of such galaxies are equal to that of their averaged massive metal-rich GCs at a given galactocentric distance, to within small uncertainties. The observed color differences between the red GC systems and their parent galaxies cannot be explained by the presence of multiple stellar generations in massive metal-rich GCs, as the impact of the latter to the populations' integrated g-z or B-I colors is found to be negligible. However, we show that this paradox can be explained if the stellar initial mass function (IMF) in these massive elliptical galaxies was significantly steeper at subsolar masses than canonical IMFs derived from star counts in the solar neighborhood, with the GC colors having become bluer due to dynamical evolution, causing a significant flattening of the stellar MF of the average surviving GC.
We discuss the implications of purely classical, instead of quantum, theory of gravity for the gravitational wave spectrum generated during inflation. We show that a positive detection of primordial gravitational waves will no longer suffice to determine the scale of inflation in this case -- even a high-scale model of inflation can bypass the observational constraints due to large uncertainties in the initial classical amplitude of the tensor modes.
Remarkable observational advances have established a compelling
cross-validated model of the Universe. Yet, two key pillars of this model --
dark matter and dark energy -- remain mysterious. Sky surveys that map billions
of galaxies to explore the `Dark Universe', demand a corresponding
extreme-scale simulation capability; the HACC (Hybrid/Hardware Accelerated
Cosmology Code) framework has been designed to deliver this level of
performance now, and into the future. With its novel algorithmic structure,
HACC allows flexible tuning across diverse architectures, including accelerated
and multi-core systems.
On the IBM BG/Q, HACC attains unprecedented scalable performance -- currently
13.94 PFlops at 69.2% of peak and 90% parallel efficiency on 1,572,864 cores
with an equal number of MPI ranks, and a concurrency of 6.3 million. This level
of performance was achieved at extreme problem sizes, including a benchmark run
with more than 3.6 trillion particles, significantly larger than any
cosmological simulation yet performed.
Using a simplified model framework, we assess observational limits and discovery prospects for neutralino dark matter, taken here to be a general admixture of bino, wino, and Higgsino. Experimental constraints can be weakened or even nullified in regions of parameter space near 1) purity limits, where the dark matter is mostly bino, wino, or Higgsino, or 2) blind spots, where the relevant couplings of dark matter to the $Z$ or Higgs bosons vanish identically. We analytically identify all blind spots relevant to spin-independent and spin-dependent scattering and show that they arise for diverse choices of relative signs among $M_1$, $M_2$, and $\mu$. At present, XENON100 and IceCube still permit large swaths of viable parameter space, including the well-tempered neutralino. On the other hand, upcoming experiments should have sufficient reach to discover dark matter in much of the remaining parameter space. Our results are broadly applicable, and account for a variety of thermal and non-thermal cosmological histories, including scenarios in which neutralinos are just a component of the observed dark matter today. Because this analysis is indifferent to the fine-tuning of electroweak symmetry breaking, our findings also hold for many models of neutralino dark matter in the MSSM, NMSSM, and Split Supersymmetry. We have identified parameter regions at low $\tan \beta$ which sit in a double blind spot for both spin-independent and spin-dependent scattering. Interestingly, these low $\tan \beta$ regions are independently favored in the NMSSM and models of Split Supersymmetry which accommodate a Higgs mass near 125 GeV.
We evaluate the effective mass of a scalar field phi coupled to thermal plasma through Planck-suppressed interactions. We find it useful to rescale the coupled fields so that all the phi-dependences are absorbed into the yukawa and gauge couplings, which allows us to read off the leading order contributions to the effective mass \tilde m_{phi} from the 2-loop free energy calculated with the rescaled couplings. We give an analytical expression for \tilde m_{phi} at a sufficiently high temperature in the case where phi is coupled to the MSSM chiral superfields through non-minimal Kahler potential. We find that \tilde m_{phi}^2 is about 10^{-3} H^2 \sim 10^{-2} H^2 for typical parameter sets, where H is the Hubble expansion rate in the radiation-dominated era.
It is shown that F(R)-modified gravitational theories lead to curvature oscillations in astrophysical systems with rising energy density. The frequency and the amplitude of such oscillations could be very high and would lead to noticeable production of energetic cosmic ray particles.
A general nonperturvative loop quantization procedure for metric modified gravity is reviewed. As an example, this procedure is applied to scalar-tensor theories of gravity. The quantum kinematical framework of these theories is rigorously constructed. Both the Hamiltonian and master constraint operators are well defined and proposed to represent quantum dynamics of scalar-tensor theories. As an application to models, we set up the basic structure of loop quantum Brans-Dicke cosmology. The effective dynamical equations of loop quantum Brans-Dicke cosmology are also obtained, which lay a foundation for the phenomenological investigation to possible quantum gravity effects in cosmology.
The complementarity between dark matter searches at colliders and in underground laboratories is an extraordinarily powerful tool in the quest for dark matter. In the vast majority of the analyses conducted so far these dark matter detection strategies have been profitably combined either to perform global fits in the context of certain particle physics models (e.g. the CMSSM) or to estimate the prospects for a direct dark matter detection given the LHC potential of discovering new physics beyond the Standard Model. In this paper we propose an alternative strategy to combine direct and collider dark matter searches: employing the potential of the upcoming generation of 1-ton direct detection experiments, we show that for certain supersymmetric configurations it is possible to translate the information encoded in an hypothetically discovered direct detection signal into classes of expected signals at the LHC. As an illustrative application of our method, we show that for a 60 GeV neutralino thermally produced via resonant annihilations and identified by a 1-ton direct detection experiment, our approach allows to forecast a clearly identifiable prediction for a LHC final state involving three leptons and missing energy. The strategy presented in this paper to systematically translate a direct detection signal into a prediction for the LHC has the potential to significantly strengthen the complementarity between these two dark matter detection strategies.
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