We present for the first time a detailed spectroscopic study of chemical element abundances of metal-poor RR Lyrae stars in the Large and Small Magellanic Cloud (LMC and SMC). Using the MagE echelle spectrograph at the 6.5m Magellan telescopes, we obtain medium resolution (R ~ 2000 - 6000) spectra of six RR Lyrae stars in the LMC and three RR Lyrae stars in the SMC. These stars were chosen because their previously determined photometric metallicities were among the lowest metallicities found for stars belonging to the old populations in the Magellanic Clouds. We find the spectroscopic metallicities of these stars to be as low as [Fe/H]_{spec} = -2.7dex, the lowest metallicity yet measured for any star in the Magellanic Clouds. We confirm that for metal-poor stars, the photometric metallicities from the Fourier decomposition of the lightcurves are systematically too high compared to their spectroscopic counterparts. However, for even more metal-poor stars below [Fe/H]_{phot} < -2.8dex this trend is reversed and the spectroscopic metallicities are systematically higher than the photometric estimates. We are able to determine abundance ratios for ten chemical elements, which extend the abundance measurements of chemical elements for RR Lyrae stars in the Clouds beyond [Fe/H] for the first time. For the overall [alpha/Fe] ratio, we obtain an overabundance of 0.36dex, which is in very good agreement with results from metal-poor stars in the Milky Way halo as well as from the metal-poor tail in dwarf spheroidal galaxies. Comparing the abundances with those of the stars in the Milky Way halo we find that the abundance ratios of stars of both populations are consistent with another. Therefore we conclude that from a chemical point of view early contributions from Magellanic-type galaxies to the formation of the Galactic halo as claimed in cosmological models are plausible.
We combine high-resolution HST/WFC3 images with multi-wavelength photometry to track the evolution of structure and activity of massive (log(M*) > 10) galaxies at redshifts z = 1.4 - 3 in two fields of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). We detect compact, star-forming galaxies (cSFGs) whose number densities, masses, sizes, and star formation rates qualify them as likely progenitors of compact, quiescent, massive galaxies (cQGs) at z = 1.5 - 3. At z > 2 most cSFGs have specific star-formation rates (sSFR = 10^-9 yr^-1) half that of typical, massive SFGs at the same epoch, and host X-ray luminous AGN 30 times (~30%) more frequently. These properties suggest that cSFGs are formed by gas-rich processes (mergers or disk-instabilities) that induce a compact starburst and feed an AGN, which, in turn, quench the star formation on dynamical timescales (few 10^8 yr). The cSFGs are continuously being formed at z = 2 - 3 and fade to cQGs by z = 1.5. After this epoch, cSFGs are rare, thereby truncating the formation of new cQGs. Meanwhile, down to z = 1, existing cQGs continue to enlarge to match local QGs in size, while less-gas-rich mergers and other secular mechanisms shepherd (larger) SFGs as later arrivals to the red sequence. In summary, we propose two evolutionary scenarios of QG formation: an early (z > 2), fast-formation path of rapidly-quenched cSFGs that evolve into cQGs that later enlarge within the quiescent phase, and a slow, late-arrival (z < 2) path for SFGs to form QGs without passing through a compact state.
The discovery of multiple evolutionary sequences has challenged the paradigm that globular clusters (GCs) host simple stellar populations. In addition, spectroscopic studies of GCs show a spread in light-element abundances, suggesting that multiple sequences can be formed from gaseous ejecta processed in evolved cluster stars. If multiple sequences originate from within GCs, then it should be determined how such stellar systems retain gas, form new stars within them and subsequently evolve. Here we expand upon previous studies and carry out hydrodynamical simulations that explore a wide range of cluster masses, compactness, metallicities and stellar age combinations in order to determine the ideal conditions for gas retention. We find that up to 6.4% of the mass of the star cluster can be made up of retained stellar wind gas at the time star formation is triggered. However, we show that multiple episodes of star formation can take place during the lifetime of a star cluster in particular for times $\gtrsim 1$ Gyr, thus leading to a sizable enhancement in the total number of new stars. The fact that this favorable star formation time interval coincides with the asymptotic giant branch (AGB) phase seems to give further credence to the idea that, at least in some GCs, there are stars which have formed from material processed by a previous generation of stars. The ability of extended heating sources, such as pulsar outflows or accretion onto compact objects, to hamper gas retention is illustrated via a simple numerical treatment.
When transiting their host stars, hot Jupiters absorb about 10% of the light in the wings of the stellar Lyman-alpha emission line. Surprisingly, the absorption occurs at wavelengths Doppler-shifted from line center by \pm100 km/s-much larger than the speeds with which partially neutral, 7000 K hydrogen escapes from hot Jupiter atmospheres. It has been proposed that the absorption arises from 10E6 K hydrogen from the host stellar wind, made momentarily neutral by charge exchange with planetary H I. To test this proposal, we perform 2D hydrodynamic simulations of colliding hot Jupiter and stellar winds, augmented by a chemistry module to compute the amount of hot neutral hydrogen produced by charge exchange. We observe the contact discontinuity where the two winds meet to be Kelvin-Helmholtz unstable. The Kelvin-Helmholtz instability mixes the two winds; in the mixing layer, charge exchange reactions establish, within tens of seconds, a chemical equilibrium in which the neutral fraction of hot stellar hydrogen equals the neutral fraction of cold planetary hydrogen (about 20%). In our simulations, enough hot neutral hydrogen is generated to reproduce the transit observations, and the amount of absorption converges with both spatial resolution and time. We provide physical scaling relations that describe how the absorption varies with stellar and planetary wind properties; in particular the absorption scales positively but weakly with both the stellar and planetary wind densities.
There is observational evidence for inside-out growth of giant elliptical galaxies since $z \gtrsim 2-3$. Many of the $\sim 10^{11} M_{\odot}$ systems at high redshift have small sizes $\sim 1kpc$ and surface brightness profiles with low Sersic indices n. The most likely descendants at $z = 0$ have, on average, grown by a factor of two in mass and a factor of four in size. They also have surface brightness profiles with $n \gtrsim 5$. This evolution can be qualitatively explained on the basis of two assumptions: compact ellipticals predominantly grow by collisionless minor 'dry' mergers, and they are embedded in massive dark matter halos which support the stripping of merging satellite stars at large radii. We draw these conclusions from idealized collisionless mergers spheroidal galaxies - with and without dark matter - with mass ratios of 1:1, 1:5, and 1:10. For minor mergers of galaxies embedded in dark matter halos, the sizes grow significantly faster and the profile shapes change more rapidly than for major mergers. After only two 1:5 mergers the Sersic index has increased to $n > 8$, reaching a final value of $n = 9.5$ after doubling the stellar mass. This is accompanied by a significant increase ($\gtrsim 80$ per cent) of the dark matter fraction within the half-mass radius, driven by the strong size increase probing larger, dark matter dominated regions. We conclude that only a few minor mergers ($\sim 3-5$ with mass-ratios of 1:5) of galaxies embedded in massive dark matter halos can result in the observed concurrent inside-out growth and the rapid evolution in profile shapes. Apart from negative stellar metallicity gradients and, eventually, positive age gradients, such a minor merger scenario also predicts significantly lower dark matter fractions for $z \sim 2$ compact quiescent galaxies and their rare present day analogues (abbreviated).
Various formulations of smooth-particle hydrodynamics (SPH) have been proposed, intended to resolve certain difficulties in the treatment of fluid mixing instabilities. Most have involved changes to the algorithm which either introduce 'artificial' correction terms or violate what is arguably the greatest advantage of SPH over other methods: manifest conservation of energy, entropy, momentum, and angular momentum. Here, we show how a class of alternative SPH equations of motion (EOM) can be derived self-consistently from a discrete particle Lagrangian - guaranteeing manifest conservation - in a manner which tremendously improves treatment of these instabilities and contact discontinuities. Saitoh & Makino recently noted that the volume element used to discretize the EOM does not need to explicitly invoke the mass density (as in the 'standard' approach); we show how this insight can be incorporated into the rigorous Lagrangian formulation that retains ideal conservation properties and includes the 'Grad-h' terms that account for variable smoothing lengths. We derive a general EOM for any choice of volume element (particle 'weights') and method of determining smoothing lengths. We then specify this to a 'pressure-entropy formulation' which resolves problems in the traditional treatment of fluid interfaces. Implementing this in a new version of the GADGET code, we show it leads to good performance in mixing experiments (e.g. Kelvin-Helmholtz & 'blob' tests). And conservation is maintained even in strong shock/blastwave tests, where formulations without manifest conservation produce large errors. This also improves the treatment of sub-sonic turbulence, and lessens the need for large kernel particle numbers. The code changes are trivial and entail no additional numerical expense. This provides a general framework for self-consistent derivation of different 'flavors' of SPH.
The intergalactic medium was reionized before redshift z~6, most likely by starlight which escaped from early galaxies. The very first stars formed when hydrogen molecules (H2) cooled gas inside the smallest galaxies, minihalos of mass between 10^5 and 10^8 solar masses. Although the very first stars began forming inside these minihalos before redshift z~40, their contribution has, to date, been ignored in large-scale simulations of this cosmic reionization. Here we report results from the first reionization simulations to include these first stars and the radiative feedback that limited their formation, in a volume large enough to follow the crucial spatial variations that influenced the process and its observability. We show that reionization began much earlier with minihalo sources than without, and was greatly extended, which boosts the intergalactic electron-scattering optical depth and the large-angle polarization fluctuations of the cosmic microwave background significantly. Although within current WMAP uncertainties, this boost should be readily detectable by Planck. If reionization ended as late as z_ov<~7, as suggested by other observations, Planck will thereby see the signature of the first stars at high redshift, currently undetectable by any other probe.
We present SMA and CARMA continuum and spectral line observations of five dense cores located in the Perseus and Ophiuchus molecular clouds whose masses exceed their thermal Jeans masses. Three of these cores have previously been identified as being starless and two have been classified as being possibly protostellar. We find that one core is certainly protostellar. The other four cores, however, are starless and undetected in both C18O (2-1) and 1.3mm continuum emission. These four starless cores have flat density profiles out to at least 0.006 pc, which is typical for starless cores in general. Density profiles predicted by some collapse models, especially in the early stages of infall, are consistent with our observations. Archival data reveal that these starless cores have significant non-thermal support against collapse, although they may still be unstable.
Globular clusters (GCs) are the oldest stellar systems in the Milky Way. Long time considered as simple stellar populations, nowadays we recognize their complex star formation history through precise abundance analysis of a variety of chemical elements in individual cluster members. Although we do not necessarily see clues for multiple populations in all GC colour-magnitude diagrams, all GCs present significant spreads and certain anticorrelations between their light and alpha element abundances. Furthermore, the heavy element abundances in individual stars of the primordial generation and their comparison to halo field stars and dwarf galaxies could provide us with valuable information about the very first stars that could have formed in GCs. M75 is a unique outer halo (galactocentric distance of ~15 kpc) GC with a peculiar Horizontal Branch morphology. Here we present the first abundance measurements of 16 individual red giants from high resolution spectroscopy. The cluster is metal rich ([Fe/H] = -1.17 +/- 0.02), alpha-enhanced, and shows a marginal spread in [Fe/H] of 0.07 dex, typical of most GCs of similar luminosity. The O-Na anticorrelation is clearly visible, showing at least two generations of stars, formed on a short timescale. We also discuss r- and s-process element abundances in the context of the earliest cluster enrichment phases.
In this review, I present a brief summary of the impact of nucleon pairing at supra-nuclear densities on the cooling of neutron stars. I also describe how the recent observation of the cooling of the neutron star in the supernova remnant Cassiopeia A may provide us with the first direct evidence for the occurrence of such pairing. It also implies a size of the neutron 3P-F2 energy gap of the order of 0.1 MeV.
(Abridged) In this first paper of a series, we report the creation of large and well-defined database that combines extensive new measurements and a literature search of 3876 supernovae (SNe) and their 3679 host galaxies located in the sky area covered by the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8). This database should be much larger than previous ones, and should contain a homogenous set of global parameters of SN hosts, including morphological classifications and measures of nuclear activity. The measurements of apparent magnitudes, diameters (D25), axial ratios (b/a), and position angles (PA) of SN host galaxies were made using the images extracted from the SDSS g-band. For each host galaxy, we analyzed RGB images of the SDSS to accurately measure the position of its nucleus to provide the SDSS name. With these images, we also provide the host galaxy's morphological type, and note if it has a bar, a disturbed disk, and whether it is part of an interacting or merging system. In addition, the SDSS nuclear spectra were analyzed to diagnose the central power source of the galaxies. Special attention was paid to collect accurate data on the spectroscopic classes, coordinates, offsets of SNe, and heliocentric redshifts of the host galaxies. The creation of this large database will help to better understand how the different types of SNe are correlated with the properties of the nuclei and global physical parameters of the host galaxies, and minimize possible selection effects and errors that often arise when data are selected from different sources and catalogues.
It has generally been assumed in the literature that while young supernova remnants (SNRs) accelerate particles even in the early stages, the particles do not escape until the start of the Sedov-Taylor or adiabatic stage, when the maximum energy of accelerated particles is reached. These calculations however do not take into account the detailed hydrodynamical expansion in the ejecta-dominated stage, and the approach to the Sedov stage. Using analytic approximations, we explore different environments in which the SNR may evolve, and investigate how the maximum energy to which particles are accelerated, and its time evolution, depends on various parameters. We take into account the ambient magnetic field and its amplification by resonant or non-resonant modes. Our studies reveal that the maximum energy to which particles are accelerated is generally reached in the ejecta-dominated stage, much before the start of Sedov stage. For SNe evolving within the winds of their massive stars, the maximum energy is reached very early in the evolution. We briefly explore the consequences for supernova remnants expanding in surroundings such as wind-bubbles or superbubbles.
We present continuous, high-precision photometric monitoring data with 1 minute cadence of the dM3e flare star AD Leo with the {\it MOST} satellite. We observed 19 flares in 5.8 days, and find a flare frequency distribution that is similar to previous studies. The light curve reveals a sinusoidal modulation with period of $2.23^{+0.36}_{-0.27}$ days that we attribute to the rotation of a stellar spot rotating into and out of view. We see no correlation between the occurrence of flares and rotational phase, indicating that there may be many spots distributed at different longitudes, or possibly that the modulation is caused by varying surface coverage of a large polar spot that is viewed nearly pole-on. The data show no correlation between flare energy and the time since the previous flare. We use these results to reject a simple model in which all magnetic energy is stored in one active region and released only during flares.
We use Galaxy Zoo 2 visual classifications to study the morphological signatures of interaction between similar-mass galaxy pairs in the Sloan Digital Sky Survey. We find that many observable features correlate with projected pair separation; not only obvious indicators of merging, disturbance and tidal tails, but also more regular features, such as spiral arms and bars. These trends are robustly quantified, using a control sample to account for observational biases, producing measurements of the strength and separation scale of various morphological responses to pair interaction. For example, we find that the presence of spiral features is enhanced at scales < 70 h^-1 kpc, probably due to both increased star formation and the formation of tidal tails. On the other hand, the likelihood of identifying a bar decreases significantly in pairs with separations < 30 h^-1 kpc, suggesting that bars are suppressed by close interactions between galaxies of similar mass. We go on to show how morphological indicators of physical interactions provide a way of significantly refining standard estimates for the frequency of close pair interactions, based on velocity offset and projected separation. The presence of loosely wound spiral arms is found to be a particularly reliable signal of an interaction, for projected pair separations up to \sim 100 h^-1 kpc. We use this indicator to demonstrate our method, constraining the fraction of low-redshift galaxies in truly interacting pairs, with M_{\ast} > 10^9.5 M_\odot and mass ratio < 4, to be between 0.4 - 2.7 per cent.
We present a unified model for the structure and appearance of accretion powered sources across their entire luminosity range from galactic X-ray binaries to luminous quasars, with emphasis on AGN and their phenomenology. Central to this model is the notion of MHD winds launched from the accretion disks that power these objects. These winds provide the matter that manifests as blueshifted absorption features in the UV and X-ray spectra of a large fraction of these sources; furthermore, their density distribution in the poloidal plane determines the "appearance" (i.e. the column and velocity structure of these absorption features) as a function of the observer inclination angle. This work focuses on just the broadest characteristics of these objects; nonetheless, it provides scaling laws that allow one to reproduce within this model the properties of objects spanning a very wide luminosity range and viewed at different inclination angles, and trace them to a common underlying dynamical structure. Its general conclusion is that the AGN phenomenology can be accounted for in terms of three parameters: The wind mass flux in units of the Eddington value, $\dot m$, the observer's inclination angle $\theta$ and the logarithmic slope between the O/UV and X-ray fluxes $\alpha_{OX}$. However, because of a significant correlation between $\alpha_{OX}$ and UV luminosity, we conclude that the AGN structure depends on only two parameters. Interestingly, the correlations implied by this model appear to extend to and consistent with the characteristics of galactic X-ray sources, suggesting the presence of a truly unified underlying structure for accretion powered sources.
Over the past couple of years, a number of observational studies have confirmed the outer flattening of the radial velocity dispersion profiles for stars in various nearby globular clusters. Under Newtonian gravity, this is explained by invoking tidal heating from the overall Milky Way potential on the outer, more loosely bound stars, of the globular clusters in question. From the point of view of modified gravity theories, such an outer flattening is expected on crossing the critical acceleration threshold $a_{0}$, beyond which, a transition to MONDian dynamics is expected, were equilibrium velocities cease to be a function of distance. In this paper we attempt to sort out between the above competing explanations, by looking at their plausibility in terms of an strictly empirical approach. We determine Newtonian tidal radii using masses accurately calculated through stellar population modelling, and hence independent of any dynamical assumptions, distances, size and orbital determinations for the sample of 8 globular clusters studied. We show that their Newtonian tidal radii, in all cases, at perigalacticon, are larger that the radii at which the flattening in the velocity dispersion profiles occur, by large factors of 2-10. While this point makes the Newtonian tidal explanation extremely suspect, it is found that the radii at which the flattening is observed nicely correlates with the radii where the $a_{0}$ threshold is crossed, that the fractional fall in the velocity dispersion profile correlates with the fraction of the cluster lying within the $a_{0}$ threshold, and that $\sigma_{\infty}$ values scale with the fourth root of the total masses, all features predicted under modified gravity theories.
There is growing interest in testing alternative gravity theories using the subtle Gravitational Redshifts in clusters of galaxies. However, current models all neglect a Transverse Doppler redshift of similar magnitude, and some models are not self-consistent. An equilibrium model would fix the Gravitational and Transverse Doppler velocity shifts to be about 6\sigma^2/c and 3\sigma^2/2c in order to fit the observed velocity dispersion \sigma self-consistently. This result is from the Virial Theorem for a spherical isotropic cluster, and is insensitive to the theory of gravity. In any case, a gravitational redshift signal cannot directly distinguish between the Einsteinian and f(R) gravity theories, because the mass of the cluster dark halo must be treated as an unknown fitting parameter, whose value must vary according to the theory adopted, otherwise the system would be in equilibrium in one gravity theory and out of equilibrium in another.
We compare the cosmological first-order post-Newtonian (1PN) approximation with the relativistic cosmological linear perturbation theory in a zero-pressure medium with the cosmological constant. We compare equations and solutions in several different gauge conditions available in both methods. In the PN method we have perturbation equations for density, velocity and gravitational potential independently of the gauge condition to 1PN order. However, correspondences with these 1PN equations are available only in certain gauge conditions in the perturbation theory. Equations of perturbed velocity and the perturbed gravitational potential in the zero-shear gauge exactly coincide with the Newtonian equations which remain valid even to 1PN order (the same is true for perturbed velocity in the comoving gauge), and equations of perturbed density in the zero-shear gauge and the uniform-expansion gauge coincide to 1PN order. We identify other correspondences available in different gauge conditions of the perturbation theory.
We review an optimal-filter-based algorithm for detecting candidate sources of unknown and differing size embedded in a stochastic background, and its application to detecting candidate cosmic bubble collision signatures in Wilkinson Microwave Anisotropy Probe (WMAP) 7-year observations. The algorithm provides an enhancement in sensitivity over previous methods by a factor of approximately two. Moreover, it is optimal in the sense that no other filter-based approach can provide a superior enhancement of these signatures. Applying this algorithm to WMAP 7-year observations, eight new candidate bubble collision signatures are detected for follow-up analysis.
The polar motion data is analyzed to obtain accurate position of the figure axis referred to the Earth-fixed frame. The variation of the figure axis should be the basic object to which the geophysical events are linked. By the method of rigid dynamics, the relation between the rotational and the figure axes is derived. The polar motion is the motion of the rotational axis on the Earth's surface and therefore the exact position of the figure axis on the surface at each moment is obtained from the polar motion. Since the accuracy of the recent data for the polar motion is very high, the obtained position of the figure axis is considered to keep good quality. As an average for a long duration of time, the obtained figure axis exhibits stable annual and semi-annual variations while it has no component with the period of the Chandler wobble. Besides this general feature, it shows different patterns from year to year as well as small irregularities with shorter periods, most of which are considered to be significant but not attributed to the observational errors. Further, a simple model is introduced for the cause of the seasonal variation of the figure axis. The model explains both the variation of the figure axis obtained above and that of the rotational speed which is so far known.
The fraction of compact active galactic nuclei (AGNs) that exhibit interstellar scintillation (ISS) at radio wavelengths, as well as their scintillation amplitudes, have been found to decrease significantly for sources at redshifts z > 2. This can be attributed to an increase in the angular sizes of the \muas-scale cores or a decrease in the flux densities of the compact \muas cores relative to that of the mas-scale components with increasing redshift, possibly arising from (1) the space-time curvature of an expanding Universe, (2) AGN evolution, (3) source selection biases, (4) scatter broadening in the ionized intergalactic medium (IGM) and intervening galaxies, or (5) gravitational lensing. We examine the frequency scaling of this redshift dependence of ISS to determine its origin, using data from a dual-frequency survey of ISS of 128 sources at 0 < z < 4. We present a novel method of analysis which accounts for selection effects in the source sample. We determine that the redshift dependence of ISS is partially linked to the steepening of source spectral indices ({\alpha}^8.4_4.9) with redshift, caused either by selection biases or AGN evolution, coupled with weaker ISS in the {\alpha}^8.4_4.9 < -0.4 sources. Selecting only the -0.4 < {\alpha}^8.4_4.9 < 0.4 sources, we find that the redshift dependence of ISS is still significant, but is not significantly steeper than the expected (1+z)^0.5 scaling of source angular sizes due to cosmological expansion for a brightness temperature and flux-limited sample of sources. We find no significant evidence for scatter broadening in the IGM, ruling it out as the main cause of the redshift dependence of ISS. We obtain an upper limit to IGM scatter broadening of < 110\muas at 4.9 GHz with 99% confidence for all lines of sight, and as low as < 8\muas for sight-lines to the most compact, \sim 10\muas sources.
We revisit the causal backreaction paradigm, in which the need for Dark Energy is eliminated via the generation of an apparent cosmic acceleration from the causal flow of inhomogeneity information coming in towards each observer from distant structure-forming regions. This second-generation formalism incorporates "recursive nonlinearities": the process by which already-established metric perturbations will then act to slow down all future flows of inhomogeneity information. Here, the long-range effects of causal backreaction are now damped, weakening its impact for models that were previously best-fit cosmologies. Nevertheless, we find that causal backreaction can be recovered as a replacement for Dark Energy via the adoption of larger values for the dimensionless `strength' of the clustering evolution functions being modeled -- a change justified by the hierarchical nature of clustering and virialization in the universe, occurring on multiple cosmic length scales simultaneously. With this, and with one new model parameter representing the slowdown of clustering due to astrophysical feedback processes, an alternative cosmic concordance can once again be achieved for a matter-only universe in which the apparent acceleration is generated entirely by causal backreaction effects. One drawback is a new degeneracy which broadens our predicted range for the observed jerk parameter $j_{0}^{\mathrm{Obs}}$, thus removing what had appeared to be a clear signature for distinguishing causal backreaction from Cosmological Constant $\Lambda$CDM. As for the long-term fate of the universe, incorporating recursive nonlinearities appears to make the possibility of an `eternal' acceleration due to causal backreaction far less likely; though this does not take into account gravitational nonlinearities or the large-scale breakdown of cosmological isotropy, effects not easily modeled within this formalism.
Presently only 30% of short gamma ray bursts (SGRBs) have accurate redshifts, and this sample is highly biased by the limited sensitivity of {\it Swift} to detect SGRBs. We account for the dominant biases to calculate a realistic SGRB rate density out to $z = 0.5$ using the {\it Swift} sample of peak fluxes, redshifts, and those SGRBs with a beaming angle constraint from X-ray/optical observations. Assuming a significant fraction of binary neutron star mergers produce SGRBs, we calculate lower and upper detection rate limits of (1-180) per Yr by an advanced LIGO and Virgo coincidence search. Our detection rate is compatible with extrapolations using Galactic pulsar observations and population synthesis.
The Plateau de Bure Interferometer has been used to map the continuum emission at 3.4 mm and 1.1 mm together with the J=1->0 and J=3->2 lines of HCN and HCO+ towards the binary star GV Tau. The 3.4 mm observations did not resolve the binary components and the HCN J=1->0 and HCO+ J=1->0 line emissions trace the circumbinary disk and the flattened envelope. However, the 1.1 mm observations resolved the individual disks of GV Tau N and GV Tau S and allowed us to study their chemistry. We detected the HCN 3->2 line only towards the individual disk of GV Tau N, and the emission of the HCO+ 3->2 line towards GV Tau S. Simple calculations indicate that the 3->2 line of HCN is formed in the inner R<12 AU of the disk around GV Tau N where the HCN/HCO+ abundance ratio is >300. On the contrary, this ratio is <1.6 in the disk around GV Tau S. The high HCN abundance measured in GV Tau N is well explained by photo-chemical processes in the warm (>400K) and dense disk surface.
Through an optical campaign performed at 4 telescopes located in the northern and the southern hemispheres, plus archival data from two on-line sky surveys, we have obtained optical spectroscopy for 29 counterparts of unclassified or poorly studied hard X-ray emitting objects detected with Swift/BAT and listed in the 39 months Palermo catalogue. All these objects have also observations taken with Swift/XRT or XMM-EPIC which not only allow us to pinpoint their optical counterpart, but also to study their X-ray spectral properties (column density, power law photon index and F2-10 keV flux). We find that 28 sources in our sample are AGN; 7 are classified as type 1 while 21 are of type 2; the remaining object is a galactic cataclysmic variable. Among our type 1 AGN, we find 5 objects of intermediate Seyfert type (1.2-1.9) and one Narrow Line Seyfert 1 galaxy; for 4 out of 7 sources, we have been able to estimate the central black hole mass. Three of the type 2 AGN of our sample display optical features typical of the LINER class and one is a likely Compton thick AGN. All galaxies classified in this work are relatively nearby objects since their redshifts lie in the range 0.008-0.075; the only galactic object found lies at an estimated distance of 90 pc. We have also investigated the optical versus X-ray emission ratio of the galaxies of our sample to test the AGN unified model. For them, we have also compared the X-ray absorption (due to gas) with the optical reddening (due to dust): we find that for most of our sources, specifically those of type 1.9-2.0 the former is higher than the latter confirming early results by Maiolino et al. (2001); this is possibly due to the properties of dust in the circumnuclear obscuring torus of the AGN.
Jets and outflows accompany the mass accretion process in protostars and young stellar objects. Using a large and unbiased sample, they can be used to study statistically the local feedback they provide and the typical mass accretion history. Here we analyse such a sample of Molecular Hydrogen emission line Objects in the Serpens and Aquila part of the Galactic Plane. Distances are measured by foreground star counts with an accuracy of 25%. The resulting spacial distribution and outflow luminosities indicate that our objects sample the formation of intermediate mass objects. The outflows are unable to provide a sizeable fraction of energy and momentum to support, even locally, the turbulence levels in their surrounding molecular clouds. The fraction of parsec scale flows is one quarter and the typical dynamical jet age of the order of 1E4yrs. Groups of emission knots are ejected every 1E3yrs. This might indicate that low level accretion rate fluctuations and not FU-Ori type events are responsible for the episodic ejection of material. Better observational estimates of the FU-Ori duty cycle are needed.
Magnetic field amplification by a fast dynamo is seen in local box simulations of SN-driven ISM turbulence, where the self-consistent emergence of large-scale fields agrees very well with its mean-field description. We accordingly derive scaling laws of the turbulent transport coef- ficients in dependence of the SN rate, density and rotation. These provide the input for global simulations of regular magnetic fields in galaxies within a mean-field MHD framework. Using a Kennicutt-Schmidt relation between the star formation (SF) rate and midplane density, we can reduce the number of free parameters in our global models. We consequently present dynamo models for different rotation curves and radial density distributions.
We conducted a spectropolarimetic survey of 58 high proper-motion white dwarfs which achieved uncertainties of >2 kG in the Halpha line and >5 kG in the upper Balmer line series. The survey aimed at detecting low magnetic fields (< 100 kG) and helped identify the new magnetic white dwarfs NLTT 2219, with a longitudinal field B_l = -97 kG, and NLTT 10480 (B_l=-212 kG). Also, we report the possible identification of a very low-field white dwarf with B_l = -4.6 kG. The observations show that ~5% of white dwarfs harbour low fields (~10 to ~10^2 kG) and that increased survey sensitivity may help uncover several new magnetic white dwarfs with fields below ~1 kG. A series of observations of the high field white dwarf NLTT 12758 revealed changes in polarity occurring within an hour possibly associated to an inclined, fast rotating dipole. Also, the relative strength of the pi and sigma components in NLTT 12758 possibly revealed the effect of a field concentration ("spot"), or, most likely, the presence of a non-magnetic white dwarf companion. Similar observations of NLTT 13015 also showed possible polarity variations, but without a clear indication of the timescale. The survey data also proved useful in constraining the chemical composition, age and kinematics of a sample of cool white dwarfs as well as in constraining the incidence of double degenerates.
We analyse the possibility that our Universe could be described by the model recently proposed by Melia & Shevchuk (2012), where the Hubble scale R_h = c/H is at all times equal to the distance ct that light has travelled since the Big Bang. In such a model, the scale factor is proportional to cosmic time and there is no acceleration nor deceleration of the expansion. We first point out problems with the very foundations of the model and its consequences for the evolution of the Universe. Next, we compare predictions of the model with observational data. As probes of the expansion we use distance data of supernovae type Ia, as well as Hubble rate data obtained from cosmic chronometers and radial baryon acoustic oscillations. We analyse the redshift evolution of the Hubble parameter and its redshift derivatives, together with the so-called O_m diagnostic and the deceleration parameter. To reliably estimate smooth functions and their derivatives from discrete data, we use the recently developed Gaussian Processes in Python package (GaPP). Our general conclusion is that the discussed model is strongly disfavoured by observations, especially at low redshifts (z < 0.5). In particular, it predicts specific constant values for the deceleration parameter and for redshift derivatives of the Hubble parameter, which is ruled out by the data.
Magnetic fields have been measured around Asymptotic Giant Branch (AGB) stars of all chemical types using maser polarization observations. If present, a large-scale magnetic field would lead to X-ray emission, which should be observable using current X-ray observatories. The aim of this work is to search the archival data for AGB stars that are intrinsic X-ray emitters. We have searched the ROSAT, CXO, and XMM archives for serendipitous X-ray observations of a sample of ~500 AGB stars. We specifically searched for the AGB stars detected with GALEX. The data is calibrated, analyzed and the X-ray luminosities and temperatures are estimated as functions of the circumstellar absorption. We identify 13 AGB stars as having either serendipitous or targeted observations in the X-ray data archives, however for a majority of the sources the detailed analysis show that the detections are questionable. Two new sources are detected by ROSAT: T Dra and R UMa. The spectral analysis suggests that the emission associated with these sources could be due to coronal activity or interaction across a binary system. Further observations of the detected sources are necessary to clearly determine the origin of the X-ray emission. Moreover, additional objects should be subject to targeted X-ray observations in order to achieve better constraints for the magnetic fields around AGB stars.
The general context of this study concerns the post-processing of multiline spectropolarimetric observations of stars, and in particular these numerical analysis techniques aiming at the detection and the characterization of polarized signatures. Hereafter, using real observational data, we compare and clarify a number of points concerning various methods of analysis. Indeed, simple line addition, least-squares deconvolution and denoising by principal component analysis have been applied, and compared to each other, to polarized stellar spectra available from the TBLegacy database of the Narval spectropolarimeter. Such a comparison between various approaches of distinct sophistication levels allows us to make a safe choice for the next implementation of on-line post-processing of our unique database for the stellar physics community.
We present new spectroscopic identifications of 12 X-shaped radio galaxies and use the spectral data to derive starburst histories and masses of the nuclear supermassive black holes in these galaxies. The observations were done with the 2.1-m telescope of the Observatorio Astron\'omico Nacional at San Pedro M\'artir, M\'exico. The new spectroscopic results extend the sample of X-shaped radio galaxies studied with optical spectroscopy. We show that the combined sample of the X-shaped radio galaxies has statistically higher black holes masses and older episodes of star formation than a control sample of canonical double-lobed radio sources with similar redshifts and luminosities. The data reveal enhanced star formation activity in the X-shaped sample at timescales expected in galactic mergers. We discuss the results obtained in the framework of the merger scenario.
PSR J1357-6429 is a Vela-like radio pulsar that has been recently detected with Chandra and Fermi, which, like Vela, powers a compact X-ray pulsar wind nebula and X-ray-radio plerion associated with an extended TeV source. We present our deep optical observations with the Very Large Telescope to search for an optical counterpart of the pulsar and its nebula. We detected a point-like source in V, R, and I bands whose position is in agreement with the X-ray position of the pulsar, and whose colours are distinct from those of ordinary stars. The tentative optical luminosity and efficiency of the source are similar to those of the Vela pulsar, which also supports the optical identification. However, the source spectrum is unusually steep, with a spectral index of about 5, which is not typical of optical pulsars. The source offset from the radio position of PSR J1357-6429, which is in line with the corresponding offset of the X-ray position, implies the pulsar transverse velocity of 1600-2000 km/s at the distance of 2-2.5 kpc, making it the fastest moving pulsar known.
The Magnetism in Massive Stars (MiMeS) survey represents a high precision systematic search for magnetic fields in hot, massive OB stars. To date, MiMeS Large Programs (ESPaDOnS@CFHT, Narval@TBL, HARPSpol@ESO3.6) and associated PI programs (FORS@VLT) have yielded nearly 1200 circular spectropolarimetric observations of over 350 OB stars. Within this sample, 20 stars are detected as magnetic. Follow-up observations of new detections reveals (i) a large diversity of magnetic properties, (ii) evidence for magnetic wind confinement in optical spectra of all magnetic O stars, (iii) the presence of strong, organized magnetic fields in all known Galactic Of?p stars, and iv) a complete absence of magnetic fields in classical Be stars.
We used the Palomar Testbed Interferometer (PTI) to resolve 2.2 $\mu$m emission from the classical nova V458 Vul 2007 over the course of several days following its discovery on 2007 August 8.54 UT. We also obtained K-band photometric data and spectra of the nova during the early days of the outburst. We also used photometric measurements from the AAVSO database. This is a unique data set offering a 3-technique approach: high-resolution imaging, spectroscopy and photometry. Our analysis shows that the nova ejecta can be modeled as an inclined disk at low inclination i.e. low ellipticity which is consistent with the nova being in the fireball phase at which the outflowing gas is optically thick, confirmed by the presence of strong P-Cygni Balmer lines in the spectra. The expansion velocity is $\approx$1700 $\rm km\ s^{-1}$, derived from the H$\alpha$ line. By combining the nova's angular expansion rate measured by PTI with the expansion rate measured from spectroscopy, the inferred distance to the nova is 9.9-11.4 kpc. We also used the K-band fluxes and the derived size of the emission to estimate the total mass ejected from the nova $\approx 4\times 10^{-4} M_{\odot}$. The quick transition of the nova from Fe II to He/N class makes V458 Vul 2007 a hybrid nova.
We report the results of Faraday rotation measurements of 23 background radio sources whose lines of sight pass through or close to the Rosette Nebula. The Rosette Nebula is an excellent candidate for studies of super bubbles associated with young star clusters. We made linear polarization measurements with the Karl G. Jansky Very Large Array (JVLA) at frequencies of 4.4GHz, 4.9GHz, and 7.7GHz. We are able to establish a background rotation measure in this part of the sky due to the Galaxy of +147 rad m^-2. Sources whose lines of sight pass through the nebula have an excess rotation measure of 50-750 rad m^-2, which we attribute to the plasma shell of the Rosette Nebula. We consider two simple plasma shell models and how they reproduce the magnitude and sign of the rotation measure, and its dependence on distance from the center of the nebula. These two models represent different modes of interaction of the Rosette Nebula star cluster with the surrounding interstellar medium. Both can reproduce the magnitude and spatial extent of the rotation measure enhancement, given plausible free parameters. We contend that the model based on a stellar bubble more closely reproduces the observed dependence of rotation measure on distance from the center of the nebula.
The dynamics of expansion and large scale structure formation of the Universe are analyzed for models with dark energy in the form of a phantom scalar field which initially mimics a $\Lambda$-term and evolves slowly to the Big Rip singularity. The discussed model of dark energy has three parameters -- the density and the equation of state parameter at the current epoch, $\Omega_{de}$ and $w_0$, and the asymptotic value of the equation of state parameter at $a\rightarrow\infty$, $c_a^2$. Their best-fit values are determined jointly with all other cosmological parameters by the MCMC method using observational data on CMB anisotropies and polarization, SNe Ia luminosity distances, BAO measurements and more. Similar computations are carried out for $\Lambda$CDM and a quintessence scalar field model of dark energy. It is shown that the current data slightly prefer the phantom model, but the differences of maximum likelihoods are not statistically significant. It is also shown that the phantom dark energy with monotonicaly increasing density in future will cause the decaying of large scale linear matter density perturbations due to the gravitational domination of dark energy perturbations long before the Big Rip singularity.
We study the effects of perturbative reheating on the evolution of the curvature perturbation \zeta, in two-field inflation models. We use numerical methods to explore the sensitivity of f_NL, n_s and r to the reheating process, and present simple qualitative arguments to explain our results. In general, if a large non-Gaussian signal exits at the start of reheating, it will remain non zero at the end of reheating. Unless all isocurvature modes have completely decayed before the start of reheating, we find that the non-linearity parameter, f_NL, can be sensitive to the reheating timescale, and that this dependence is most appreciable for `runaway' inflationary potentials that only have a minimum in one direction. For potentials with a minimum in both directions, f_NL can also be sensitive to reheating if a mild hierarchy exists between the decay rates of each field. Within the class of models studied, we find that the spectral index n_s, is fairly insensitive to large changes in the field decay rates, indicating that n_s is a more robust inflationary observable, unlike the non-linearity parameter f_NL. Our results imply that the statistics of \zeta, especially f_NL, can only be reliably used to discriminate between models of two-field inflation if the physics of reheating are properly accounted for.
We present the gamma-ray, X-ray, optical and radio data for GRB100814A. At the end of the slow decline phase of the X-ray and optical afterglow, a sudden and prominent rebrightening in the optical band occurs followed by a fast decay in both bands. This optical rebrightening is accompanied by possible chromatic variations. We discuss possible interpretations, such as double component scenarios and internal dissipation mechanism, with their virtues and drawbacks. We also compare GRB100814A with other Swift bursts that show optical rebrightenings with similar properties.
The strength of Titan's methane cycle, as measured by precipitation and evaporation, is key to interpreting fluvial erosion and other indicators of the surface-atmosphere exchange of liquids. But the mechanisms behind the occurrence of large cloud outbursts and precipitation on Titan have been disputed. A gobal- and annual-mean estimate of surface fluxes indicated only 1% of the insolation, or $\sim$0.04 W/m$^2$, is exchanged as sensible and/or latent fluxes. Since these fluxes are responsible for driving atmospheric convection, it has been argued that moist convection should be quite rare and precipitation even rarer, even if evaporation globally dominates the surface-atmosphere energy exchange. In contrast, climate simulations that allow atmospheric motion indicate a robust methane cycle with substantial cloud formation and/or precipitation. We argue the top-of-atmosphere radiative imbalance -- a readily observable quantity -- is diagnostic of horizontal heat transport by Titan's atmosphere, and thus constrains the strength of the methane cycle. Simple calculations show the top-of-atmosphere radiative imbalance is $\sim$0.5-1 W/m$^2$ in Titan's equatorial region, which implies 2-3 MW of latitudinal heat transport by the atmosphere. Our simulation of Titan's climate suggests this transport may occur primarily as latent heat, with net evaporation at the equator and net accumulation at higher latitudes. Thus the methane cycle could be 10-20 times previous estimates. Opposing seasonal transport at solstices, compensation by sensible heat transport, and focusing of precipitation by large-scale dynamics could further enhance the local, instantaneous strength of Titan's methane cycle by a factor of several.
Aims: In this paper, we focus on the kinematical properties of a proto-binary to study the infall and rotation of gas towards its two protostellar components. Methods: We present ALMA Science Verification observations with high-spectral resolution of IRAS 16293-2422 at 220.2 GHz. The wealth of molecular lines in this source and the very high spectral resolution offered by ALMA allow us to study the gas kinematics with unprecedented detail. Results: We present the first detection of an inverse P-Cygni profile towards source B in the three brightest lines. The line profiles are fitted with a simple two-layer model to derive an infall rate of 4.5x10^-5 Msun/yr. This infall detection would rule-out the previously suggested possibility of source B being a T Tauri star. A position velocity diagram for source A shows evidence for rotation with an axis close to the line-of-sight.
We present high-resolution, long-slit spectroscopic observations of five compact ($\leq$ 10 arcsec) planetary nebulae located close to the galactic bulge region and for which no high spatial resolution images are available. The data have been drawn from the San Pedro M\'artir kinematic catalogue of galactic planetary nebulae (L\'opez et al. 2012). The central star in four of these objects (M 1-32, M 2-20, M 2-31 and M 3-15) is of WR-type and the fifth object (M 2-42) has a wels type nucleus. These observations reveal the presence in all of them of a dense and thick equatorial torus-like component and high-speed, collimated, bipolar outflows. The code SHAPE is used to investigate the main morpho-kinematic characteristics and reproduce the 3-D structure of these objects assuming a cylindrical velocity field for the bipolar outflows and a homologous expansion law for the torus/ring component. The deprojected expansion velocities of the bipolar outflows are found to be in the range of 65 to 200 km $\rm{s^{-1}}$, whereas the torus/ring component shows much slower expansion velocities, in the range of 15 to 25 km $\rm{s^{-1}}$. It is found that these planetary nebulae have very similar structural components and the differences in their emission line spectra derive mostly from their different projections on the sky. The relation of their morpho-kinematic characteristics with the WR-type nuclei deserves further investigation.
An occulter is a large diffracting screen which may be flown in conjunction with a telescope to image extrasolar planets. The edge is shaped to minimize the diffracted light in a region beyond the occulter, and a telescope may be placed in this dark shadow to view an extrasolar system with the starlight removed. Errors in position, orientation, and shape of the occulter will diffract additional light into this region, and a challenge of modeling an occulter system is to accurately and quickly model these effects. We present a fast method for the calculation of electric fields following an occulter, based on the concept of the boundary diffraction wave: the 2D structure of the occulter is reduced to a 1D edge integral which directly incorporates the occulter shape, and which can be easily adjusted to include changes in occulter position and shape, as well as the effects of sources---such as exoplanets---which arrive off-axis to the occulter. The structure of a typical implementation of the algorithm is included.
ZDI studies have shown that the magnetic fields of T Tauri stars can be significantly more complex than a simple dipole and can vary markedly between sources. We collect and summarize the magnetic field topology information obtained to date and present Hertzsprung-Russell (HR) diagrams for the stars in the sample. Intriguingly, the large scale field topology of a given pre-main sequence (PMS) star is strongly dependent upon the stellar internal structure, with the strength of the dipole component of its multipolar magnetic field decaying rapidly with the development of a radiative core. Using the observational data as a basis, we argue that the general characteristics of the global magnetic field of a PMS star can be determined from its position in the HR diagram. Moving from hotter and more luminous to cooler and less luminous stars across the PMS of the HR diagram, we present evidence for four distinct magnetic topology regimes. Stars with large radiative cores, empirically estimated to be those with a core mass in excess of ~40 per cent of the stellar mass, host highly complex and dominantly non-axisymmetric magnetic fields, while those with smaller radiative cores host axisymmetric fields with field modes of higher order than the dipole dominant (typically, but not always, the octupole). Fully convective stars stars above ~0.5 MSun appear to host dominantly axisymmetric fields with strong (kilo-Gauss) dipole components. Based on similarities between the magnetic properties of PMS stars and main sequence M-dwarfs with similar internal structures, we speculate that a bistable dynamo process operates for lower mass stars (<~0.5 MSun at an age of a few Myr) and that they will be found to host a variety of magnetic field topologies. If the magnetic topology trends across the HR diagram are confirmed they may provide a new method of constraining PMS stellar evolution models.
Multi-wavelength astronomical studies require cross-identification of detections of the same celestial objects in multiple catalogs based on spherical coordinates and other properties. Because of the large data volumes and spherical geometry, the symmetric N-way association of astronomical detections is a computationally intensive problem, even when sophisticated indexing schemes are used to exclude obviously false candidates. Legacy astronomical catalogs already contain detections of more than a hundred million objects while the ongoing and future surveys will produce catalogs of billions of objects with multiple detections of each at different times. The varying statistical error of position measurements, moving and extended objects, and other physical properties make it necessary to perform the cross-identification using a mathematically correct, proper Bayesian probabilistic algorithm, capable of including various priors. One time, pair-wise cross-identification of these large catalogs is not sufficient for many astronomical scenarios. Consequently, a novel system is necessary that can cross-identify multiple catalogs on-demand, efficiently and reliably. In this paper, we present our solution based on a cluster of commodity servers and ordinary relational databases. The cross-identification problems are formulated in a language based on SQL, but extended with special clauses. These special queries are partitioned spatially by coordinate ranges and compiled into a complex workflow of ordinary SQL queries. Workflows are then executed in a parallel framework using a cluster of servers hosting identical mirrors of the same data sets.
Collisions between cosmic bubbles of different vacua are a generic feature of false vacuum eternal inflation scenarios. While previous studies have focused on the consequences of a single collision event in an observer's past, we begin here an investigation of the more general scenario allowing for many "mild" collisions intersecting our past light cone (and one another). We discuss the general features of multiple collision scenarios and consider their impact on the cosmic microwave background (CMB) temperature power spectrum, treating the collisions perturbatively. In a large class of models, one can approximate a multiple collision scenario as a superposition of individual collision events governed by nearly isotropic and scale-invariant distributions, most appearing to take up less than half of the sky. In this case, the shape of the expected CMB temperature spectrum maintains statistical isotropy and typically features a dramatic increase in power in the low multipoles relative to that of the best-fit $\Lambda$CDM model, which is in tension particularly with the observed quadrupole. We argue that this predicted spectrum is largely model-independent and can be used to outline features of the underlying statistical distributions of colliding bubbles consistent with CMB temperature measurements.
The main objective of this article is to derive a new set of gravitational field equations and to establish a new unified theory for dark energy and dark matter. The new gravitational field equations with scalar potential are derived using the Einstein-Hilbert functional, and the scalar potential is a natural outcome of the divergence-free constraint of the variational elements. Associated with this scalar potential is the scalar potential energy density $\Phi$, which represents a new type of energy caused by the non-uniform distribution of matter in the universe. The negative part of this potential energy density $\Phi$ represents the dark matter, which produces attraction, and the positive part represents the dark energy, which drives the acceleration of expanding galaxies. In addition, this potential energy density $\Phi$ is conserved with mean zero: $\int_M \Phi dM=0$. Furthermore, the new field equations resolve a few difficulties encountered by the classical Einstein field equations.
We clarify how magnetic reconnection can be derived from magnetohydrodynamics (MHD) equations in a way that is easily understandable to university students. The essential mechanism governing the time evolution of the magnetic field is diffusion dynamics. The magnetic field is represented by two components. It is clarified that the diffusion of a component causes a generation of another component that is initially zero and, accordingly, that the magnetic force lines are reconnected. For this reconnection to occur correctly, the initial magnetic field must be directed oppositely in the two regions, e.g., $y>0$ and $y<0$; must be concave (convex) for $y>0$ ($y<0$); and must be saturated for $y$ far from the x axis, which would indicate the existence of the current sheet. It will be clear that our comprehension based on diffusion runs parallel to the common qualitative explanation about the magnetic reconnection.
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The Euclid mission is the second M-class mission of the ESA Cosmic Vision programme, with the principal science goal of studying dark energy through observations of weak lensing and baryon acoustic oscillations. Euclid is also expected to undertake additional Legacy Science programmes. One such proposal is the Exoplanet Euclid Legacy Survey (ExELS) which will be the first survey able to measure the abundance of exoplanets down to Earth mass for host separations from ~1 AU out to the free-floating (unbound) regime. The cold and free-floating exoplanet regimes represent a crucial discovery space for testing planet formation theories. ExELS will use the gravitational microlensing technique and will detect over 400 microlensing events per month over 1.6 deg^2 of the Galactic bulge. We assess how many of these events will have detectable planetary signatures using a detailed multi-wavelength microlensing simulator --- the Manchester-Besancon microLensing Simulator (MaBuLS) --- which incorporates the Besancon Galactic model with 3D extinction. MaBuLS is the first theoretical simulation of microlensing to treat the effects of point spread function (PSF) blending self-consistently with the underlying Galactic model. We use MaBuLS, together with current numerical models for the Euclid PSFs, to explore a number of designs and de-scope options for ExELS, including the two current spacecraft designs, the exoplanet yield as a function of filter choice, and the effect of systematic photometry errors. Using conservative extrapolations of current empirical exoplanet mass functions determined from ground-based microlensing and radial velocity surveys, ExELS can expect to detect a few hundred cold exoplanets around mainly G, K and M-type stellar hosts, including ~19 Earth-mass planets and ~3 Mars-mass planets for an observing programme totalling 10 months.
Turbulent properties of the quiet Sun represent the basic state of surface conditions, and a background for various processes of solar activity. Therefore understanding of properties and dynamics of this `basic' state is important for investigation of more complex phenomena, formation and development of observed phenomena in the photosphere and atmosphere. For characterization of the turbulent properties we compare kinetic energy spectra on granular and sub-granular scales obtained from infrared TiO observations with the New Solar Telescope (Big Bear Solar Observatory) and from 3D radiative MHD numerical simulations ('SolarBox' code). We find that the numerical simulations require a high spatial resolution with 10 - 25 km grid-step in order to reproduce the inertial (Kolmogorov) turbulence range. The observational data require an averaging procedure to remove noise and potential instrumental artifacts. The resulting kinetic energy spectra show a good agreement between the simulations and observations, opening new perspectives for detailed joint analysis of more complex turbulent phenomena on the Sun, and possibly on other stars. In addition, using the simulations and observations we investigate effects of background magnetic field, which is concentrated in self-organized complicated structures in intergranular lanes, and find an increase of the small-scale turbulence energy and its decrease at larger scales due to magnetic field effects.
Cosmological surveys aim to use the evolution of the abundance of galaxy clusters to accurately constrain the cosmological model. In the context of LCDM, we show that it is possible to achieve the required percent level accuracy in the halo mass function with gravity-only cosmological simulations, and we provide simulation start and run parameter guidelines for doing so. Some previous works have had sufficient statistical precision, but lacked robust verification of absolute accuracy. Convergence tests of the mass function with, for example, simulation start redshift can exhibit false convergence of the mass function due to counteracting errors, potentially misleading one to infer overly optimistic estimations of simulation accuracy. Percent level accuracy is possible if initial condition particle mapping uses second order Lagrangian Perturbation Theory, and if the start epoch is between 10 and 50 expansion factors before the epoch of halo formation of interest. The mass function for halos with fewer than ~1000 particles is highly sensitive to simulation parameters and start redshift, implying a practical minimum mass resolution limit due to mass discreteness. The narrow range in converged start redshift suggests that it is not presently possible for a single simulation to capture accurately the cluster mass function while also starting early enough to model accurately the numbers of reionisation era galaxies, whose baryon feedback processes may affect later cluster properties. Ultimately, to fully exploit current and future cosmological surveys will require accurate modeling of baryon physics and observable properties, a formidable challenge for which accurate gravity-only simulations are just an initial step.
We report the spectral and temporal variability properties of 18 candidate transient and potential transient (TC and PTC) sources detected in deep multi-epoch Chandra observation of the nearby elliptical galaxies, NGC 3379, NGC 4278 and NGC 4697. Only one source can be identified with a background counterpart, leaving 17 TCs + PTCs in the galaxies. Of these, 14 are in the galaxy field, supporting the theoretical picture that the majority of field X-ray binaries (XRBs) will exhibit transient accretion for >75% of their lifetime. Three sources are coincident with globular clusters (GCs), including two high-luminosity candidate black hole (BH) XRBs, with Lx=5.4E38 erg/s, and Lx=2.8E39 erg/s, respectively. The spectra, luminosities and temporal behavior of these 17 sources suggest that the transient population is heterogeneous, including neutron star (NS) and BH XRBs in both normal and high-rate accretion modes, and super soft sources containing white dwarf binaries. Our TC and PTC detections are noticeably fewer that the number expected from the populations synthesis (PS) models of Fragos et al. (2009), tailored to our new Chandra pointings of NGC 4278. We attribute this discrepancy to the PS assumption that the transient population is composed of NS XRBs, as well as differences between the statistical analysis and error estimates used in the model and our observations.
All dark matter structures appear to follow a set of universalities, such as phase-space density or velocity anisotropy profiles, however, the origin of these universalities remains a mystery. Any equilibrated dark matter structure can be fully described by two functions, namely the radial and the tangential velocity distribution functions (VDF), and when we will understand these two then we will understand all the observed universalities. Here we demonstrate that if we know the radial VDF, then we can derive and understand the tangential VDF. This is based on simple dynamical arguments about properties of collisionless systems. We use a range of controlled numerical simulations to demonstrate the accuracy of this result. We therefore boil the question of the dark matter structural properties down to understanding the radial VDF.
We report on the discovery of GJ3470b, a transiting hot Uranus of mass m_p = 14.0+-1.8 Mearth, radius R_p = 4.2+-0.6 Rearth and period P=3.3371+-0.0002 day. Its host star is a nearby (d=25.2+-2.9pc) M1.5 dwarf of mass M_s=0.54+-0.07 Msol and radius R_s=0.50+-0.06 Rsol. The detection originates from a radial-velocity campaign with HARPS that focused on the search for short-period planets orbiting M dwarfs. Once the planet was discovered and the transit-search window narrowed to about 10% of an orbital period, a photometric search started with TRAPPIST and quickly detected the ingress of the planet. Additional observations with TRAPPIST, EulerCam and NITES definitely confirmed the transiting nature of GJ3470b and allow for the determination of its true mass and radius. The star's visible or infrared brightness (V=12.3, K=8.0 mag), together with a large eclipse depth D=0.57+-0.05%, ranks GJ3470b among the most favorable planets for follow-up characterizations.
We study the properties of two bars formed in fully cosmological hydrodynamical simulations of the formation of Milky Way-mass galaxies. In one case, the bar formed in a system with disc, bulge and halo components and is relatively strong and long, as could be expected for a system where the spheroid strongly influences the evolution. The second bar is less strong, shorter, and formed in a galaxy with no significant bulge component. We study the strength and length of the bars, the stellar density profiles along and across the bars and the velocity fields in the bar region. We compare them with the results of dynamical (idealised) simulations and with observations, and find, in general, a good agreement, although we detect some important differences as well. Our results show that more or less realistic bars can form naturally in a $\Lambda$CDM cosmology, and open up the possibility to study the bar formation process in a more consistent way than previously done, since the host galaxies grow, accrete matter and significantly evolve during the formation and evolution of the bar.
We use the joint measurement of geometry and growth from anisotropic galaxy clustering in the Baryon Oscillation Spectroscopic Survey Data Release 9 CMASS sample reported in \citet{Reid12} to constrain dark energy properties and possible deviations from the General Relativity. Assuming GR and taking a prior on the linear matter power spectrum at high redshift from the cosmic microwave background (CMB), anisotropic clustering of the CMASS DR9 galaxies alone constrains $\Omega_{\rm m} = 0.308 \pm 0.022$ and $100\Omega_{\rm k} = 5.9 \pm 4.8$ for $w = -1$, or $w = -0.91 \pm 0.12$ for $\Omega_k = 0$. When combined with the full CMB likelihood, the addition of the anisotropic clustering measurements to the spherically-averaged BAO location increases the constraining power on dark energy by a factor of 4 in a flat CDM cosmology with constant dark energy equation of state $w$ (giving $w = -0.87 \pm 0.05$). This impressive gain depends on our measurement of both the growth of structure and Alcock-Paczynski effect, and is not realised when marginalising over the amplitude of redshift space distortions. Combining with both the CMB and Supernovae Type Ia (SNeIa), we find $\Omega_{\rm m} = 0.281 \pm 0.014$ and $1000\Omega_{\rm k}=-9.2\pm5.0$ for $w = -1$, or $w_0 = -1.13 \pm 0.12$ and $w_{\rm a}=0.65 \pm 0.36$ assuming $\Omega_k = 0$. Finally, when a $\Lambda$CDM background expansion is assumed, the combination of our estimate of the growth rate with previous growth measurements provides tight constraints on the parameters describing possible deviations from GR giving $\gamma = 0.64 \pm 0.05$. For one parameter extensions of the flat $\Lambda$CDM model, we find a $\sim 2\sigma$ preference either for $w > -1$ or slower growth than in GR. However, the data is fully consistent with the concordance model, and the evidence for these additional parameters is weaker than $2\sigma$.
Under current conditions, the cosmic ray spectrum incident on the Earth is dominated by particles with energies < 1 GeV. Astrophysical sources including high energy solar flares, supernovae and gamma ray bursts produce high energy cosmic rays (HECRs) with drastically higher energies. The Earth is likely episodically exposed to a greatly increased HECR flux from such events, some of which lasting thousands to millions of years. The air showers produced by HECRs ionize the atmosphere and produce harmful secondary particles such as muons and neutrons. Neutrons currently contribute a significant radiation dose at commercial passenger airplane altitude. With higher cosmic ray energies, these effects will be propagated to ground level. This work shows the results of Monte Carlo simulations quantifying the neutron flux due to high energy cosmic rays at various primary energies and altitudes. We provide here lookup tables that can be used to determine neutron fluxes from primaries with total energies 1 GeV - 1 PeV. By convolution, one can compute the neutron flux for any arbitrary CR spectrum. Our results demonstrate that deducing the nature of primaries from ground level neutron enhancements would be very difficult.
Telescope Point Spread Function (PSF) quality is critical for realising the potential of cosmic weak lensing observations to constrain dark energy and test General Relativity. In this paper we use quantitative weak gravitational lensing measures to inform the precision of lens optical alignment, with specific reference to the Dark Energy Survey (DES). We compute optics spot diagrams and calculate the shear and flexion of the PSF as a function of position on the focal plane. For perfect optical alignment we verify the high quality of the DES optical design, finding a maximum PSF contribution to the weak lensing shear of 0.04 near the edge of the focal plane. However this can be increased by a factor of approximately three if the lenses are only just aligned within their maximum specified tolerances. We calculate the E and B-mode shear and flexion variance as a function of de-centre or tilt of each lens in turn. We find tilt accuracy to be a few times more important than de-centre, depending on the lens considered. Finally we consider the compound effect of de-centre and tilt of multiple lenses simultaneously, by sampling from a plausible range of values of each parameter. We find that the compound effect can be around twice as detrimental as when considering any one lens alone. Furthermore, this combined effect changes the conclusions about which lens is most important to align accurately. For DES, the tilt of the first two lenses is the most important.
The maximum likelihood method is often used for parameter estimation in gravitational wave astronomy. Recently, an interesting approach was proposed by Vallisneri to evaluate the distributions of parameter estimation errors expected for the method. This approach is to statistically analyze the local peaks of the likelihood surface, and works efficiently even for signals with low signal-to-noise ratios. Focusing special attention to geometric structure of the likelihood surface, we follow the proposed approach and derive formulae for a simplified model of data analysis where the target signal has only one intrinsic parameter, along with its overall amplitude. Then we apply our formulae to correlation analysis of stochastic gravitational wave background with a power-law spectrum. We report qualitative trends of the formulae using numerical results specifically obtained for correlation analysis with two Advanced-LIGO detectors.
We examine the low angular momentum flow model for Sgr A* using two-dimensional hydrodynamical calculations based on the parameters of the specific angular momentum and total energy estimated in the recent analysis of stellar wind of nearby stars around Sgr A*. The accretion flow with the plausible parameters is non-stationary and an irregularly oscillating shock is formed in the inner region of a few tens to a hundred and sixty Schwarzschild radii. Due to the oscillating shock, the luminosity and the mass-outflow rate are modulated by several per cent to a factor of 5 and a factor of 2-7, respectively, on time-scales of an hour to ten days. The flows are highly advected and the radiative efficiency of the accreting matter into radiation is very low, 10^{-5}--$10^{-3}, and the input accretion rate of 4.0* 10^{-6} solar mass/yr results in the observed luminosities -- 10^{36} erg/s of Sgr A* if a two-temperature model and the synchrotron emission are taken into account. The mass-outflow rate of the gas originating in the post-shock region increases with the increasing input specific angular momentum and ranges from a few to 99 per cent of the input accreting matter, depending on the input angular momentum. The oscillating shock is necessarily triggered if the specific angular momentum and the specific energy belong to or are located just nearby in the range of parameters responsible for a stationary shock in rotating inviscid and adiabatic accretion flow. The time variability may be relevant to the flare activity of Sgr A*.
The classic HII region M17 is one of the best studied across the electromagnetic spectrum. We present sensitive, high angular resolution observations made with the Jansky Very Large Array (JVLA) at 4.96 and 8.46 GHz that reveal the presence of 38 compact radio sources, in addition to the well known hypercompact cometary HII region M17 UC1. For this last source we find that its spectral index of value $\sim$1 is due to a gradient in opacity across its face. Of the 38 compact radio sources detected, 19 have stellar counterparts detected in the infrared, optical, or X-rays. Finally, we discuss the nature of the radio emission from the massive binary system CEN 1a and 1b, concluding that both are most probably non-thermal emitters, although the first is strongly time variable and the second is steady.
DG Tau B is a Class I young stellar source that drives the asymmetric HH 159 bipolar jet. At optical wavelengths it is obscured by circumstellar optically-thick material. Using VLA and JVLA observations, we determine for the first time the proper motions of this source and find them to be consistent, within error, with those of the nearby young star DG Tau. We also discuss an ejection event that is evident in the 1994 VLA data. As the optical and molecular outflows, this ejection traced in the radio continuum is markedly asymmetric and was detected only to the NW of the star. We propose that this knot, no longer detectable in the radio, could be observed in future optical images of DG Tau B. The positions of the VLA source and of a nearby infrared object are not coincident and we suggest that the VLA source traces the exciting object, while the infrared source could be a reflection lobe.
We use the SARS pipeline to search for planetary transits only in a small subset of the Kepler targets - the Kepler Objects of Interest (KOIs), which are already known to include at least one promising planet candidate. Although the KOIs represent less than 1% of the Kepler dataset we are able to significantly update the overall statistics of planetary multiplicity: we find 84 new transit signals on 64 systems on these light curves (LCs) only, nearly doubling the number of transit signals in these systems. 41 of the systems were singly-transiting systems that are now multiply-transiting, significantly reducing the chances of false positive in them. Notable among the new discoveries are KOI 435 as a new 6-candidate systems (where only Kepler-11 was known before), KOI 277 which includes two candidates in a 6:7 period commensurability and with anti-correlated TTVs -- all but validating the system, KOIs 719 and 1574 that have small planet candidates (1.29 R_Earth and 2.05 R_Earth respectively) in the habitable zone of their host star, and KOI 1843 that exhibits the shortest period (4.25hr) and among the smallest (0.68 R_Earth) of all planet candidates. We are also able to completely reject 11 KOIs as eclipsing binaries based on photometry alone, update the ephemeris for five KOIs and otherwise discuss a number of other objects, bringing the total of new signals and revised KOIs in this study to over a hundred. We discuss sub-optimal fitting of multi-transiting systems by the Kepler Mission that does not take Kepler's third law into account, causing the error on the d/R_* parameter to be overestimated by 3.8 (median factor). Interestingely about 1/3 of the newly detected candidates participate in period commensurabilities. We conclude that despite the phenomenal success of the Kepler mission, parallel analysis of the data by multiple teams is required to make full use of the data. [ABRIDGED]
A non-stochastic scale-independent multi-dimensional barrier model of ellipsoidal collapse for the excursion set halo mass function is presented. The key concept of our model is that a bound halo forms at the moment when the initial shear eigenvalues hit a multi-dimensional absorbing barrier of constant height in their random walking process. The multi-dimensional barrier height that characterizes the analytic halo mass function is empirically determined by fitting the numerical results from the high-resolution N-body simulation to our model. It is found that the best-fit value of the barrier height is independent of redshift and key cosmological parameters. Our analytic model with empirically determined barrier-height is shown to work excellently in the wide mass-range at various redshifts: The ratio of the model to the N-body results departs from unity by up to 5% over $10^{11}\le M/(h^{-1}M_{\odot})\le 5\times 10^{15}$ at $z=0,\ 0.5$ and 1 for both of the FoF-halo and SO-halo cases. It is also shown that our analytic model naturally explains the stochastic behaviors of the density threshold value and its log-normal distribution.
We study the nature of motion in a 3D potential composed of perturbed elliptic oscillators. Our technique is to use the results obtained from the 2D potential in order to find the initial conditions generating regular or chaotic orbits in the 3D potential. Both 2D and 3D potentials display exact periodic orbits together with extended chaotic regions. Numerical experiments suggest, that the degree of chaos increases rapidly, as the energy of the test particle increases. About 97% of the phase plane of the 2D system is covered by chaotic orbits for large energies. The regular or chaotic character of the 2D orbits is checked using the S(c) dynamical spectrum, while for the 3D potential we use the S(c) spectrum, along with the P(f) spectral method. Comparison with other dynamical indicators shows that the S(c) spectrum gives fast and reliable information about the character of motion.
We investigate the dynamical response of dark matter halos against recurrent starbursts in forming less-massive galaxies to solve the core-cusp problem, which is a discrepancy between the observation and the cold dark matter model. The gas heated by supernova feedbacks after a starburst expands, and then the star formation terminates. This expanding gas loses energy by radiative cooling, and then falls back toward the galactic center. Subsequently, a starburst arises again. This cycle of expansion and contraction of the interstellar gas leads to the recursive change in the gravitational potential of the interstellar gas. The resonance between dark matter particles and the density wave excited by the oscillating potential plays a key role to understand the physical mechanism of the cusp-core transition of dark matter halos. The dark matter halos effectively gain the kinetic energy from the energy transfer driven by the resonance between particles and the density waves. We find the critical condition for the cusp-core transition that the oscillation period of the gas potential should be approximately the same as the local dynamical time of the dark matter halo. We present the resultant core radius of the dark matter halo after the cusp-core transition induced by the resonance using the conventional mass-density profile predicted by the cold dark matter models. Moreover, we verified the analytical model using $N$-body simulations and the results nicely confirm the resonance model.
We present Spitzer IRAC (2.1 sq. deg.) and MIPS (6.5 sq. deg.) observations of star formation in the Ophiuchus North molecular clouds. This fragmentary cloud complex lies on the edge of the Sco-Cen OB association, several degrees to the north of the well-known rho Oph star-forming region, at an approximate distance of 130 pc. The Ophiuchus North clouds were mapped as part of the Spitzer Gould Belt project under the working name `Scorpius'. In the regions mapped, selected to encompass all the cloud with visual extinction AV>3, eleven Young Stellar Object (YSO) candidates are identified, eight from IRAC/MIPS colour-based selection and three from 2MASS K/MIPS colours. Adding to one source previously identified in L43 (Chen et al. 2009), this increases the number of YSOcs identified in Oph N to twelve. During the selection process, four colour-based YSO candidates were rejected as probable AGB stars and one as a known galaxy. The sources span the full range of YSOc classifications from Class 0/1 to Class III, and starless cores are also present. Twelve high-extinction (AV>10) cores are identified with a total mass of approx. 100 solar masses. These results confirm that there is little ongoing star formation in this region (instantaneous star formation efficiency <0.34%) and that the bottleneck lies in the formation of dense cores. The influence of the nearby Upper Sco OB association, including the 09V star zeta Oph, is seen in dynamical interactions and raised dust temperatures but has not enhanced levels of star formation in Ophiuchus North.
Results are presented for [CII] 158 micron line fluxes observed with the Herschel PACS instrument in 112 sources with both starburst and AGN classifications, of which 102 sources have confident detections. Results are compared with mid-infrared spectra from the Spitzer Infrared Spectrometer and with L(IR) from IRAS fluxes; AGN/starburst classifications are determined from equivalent width of the 6.2 micron PAH feature. It is found that the [CII] line flux correlates closely with the flux of the 11.3 micron PAH feature independent of AGN/starburst classification, log [f([CII] 158 micron)/f(11.3 micron PAH)] = -0.22 +- 0.25. It is concluded that [CII] line flux measures the photodissociation region associated with starbursts in the same fashion as the PAH feature. A calibration of star formation rate for the starburst component in any source having [CII] is derived comparing [CII] luminosity L([CII]) to L(IR) with the result that log SFR = log L([CII)]) - 7.08 +- 0.3, for SFR in solar masses per year and L([CII]) in solar luminosities. The decreasing ratio of L([CII]) to L(IR) in more luminous sources (the "[CII] deficit") is shown to be a consequence of the dominant contribution to L(IR) arising from a luminous AGN component because the sources with largest L(IR) and smallest L([CII])/L(IR) are AGN.
We are interested in formulating a viscous model of the universe based on The Bianchi Type IV algebra. We first begin by considering a congruence of fluid lines in spacetime, upon which, analyzing their propagation behaviour, we derive the famous Raychaudhuri equation, but, in the context of viscous fluids. We will then go through in great detail the topological and algebraic structure of a Bianchi Type IV algebra, by which we will derive the corresponding structure and constraint equations. From this, we will look at The Einstein field equations in the context of orthonormal frames, and derive the resulting dynamical equations: The \emph{Raychaudhuri Equation}, \emph{generalized Friedmann equation}, \emph{shear propagation equations}, and a set of non-trivial constraint equations. We show that for cases in which the bulk viscous pressure is significantly larger than the shear viscosity, this cosmological model isotropizes asymptotically to the present-day universe. We finally conclude by discussing The Penrose-Hawking singularity theorem, and show that the viscous universe under consideration necessarily emerged from a past singularity point.
With recent Herschel observations, the northern filament of the Corona Australis cloud has now been mapped in a number of bands from 1.2um to 870um. The data set provides a good starting point for the study of the cloud over several orders of magnitude in density. We wish to examine the differences of the column density distributions derived from dust extinction, scattering, and emission, and to determine to what extent the observations are consistent with the standard dust models. From Herschel data, we calculate the column density distribution that is compared to the corresponding data derived in the near-infrared regime from the reddening of the background stars, and from the surface brightness attributed to light scattering. We construct three-dimensional radiative transfer models to describe the emission and the scattering. The scattered light traces low column densities of A_V~1mag better than the dust emission, remaining useful to A_V ~ 10-15 mag. Based on the models, the extinction and the level of dust emission are surprisingly consistent with a sub-millimetre dust emissivity typical of diffuse medium. However, the intensity of the scattered light is very low at the centre of the densest clump and this cannot be explained without a very low grain albedo. Both the scattered light and dust emission indicate an anisotropic radiation field. The modelling of the dust emission suggests that the radiation field intensity is at least three times the value of the normal interstellar radiation field. The inter-comparison between the extinction, light scattering, and dust emission provides very stringent constraints on the cloud structure, the illuminating radiation field, and the grain properties.
Massive stars are essential to understand a variety of branches of astronomy
including galaxy and star cluster evolution, nucleosynthesis and supernovae,
pulsars and black holes. It has become evident that massive star evolution is
very diverse, being sensitive to metallicity, binarity, rotation, and possibly
magnetic fields. While the problem to obtain a good statistical observational
database is alleviated by current large spectroscopic surveys, it remains a
challenge to model these diverse paths of massive stars towards their violent
end stage.
We show that the main sequence stage offers the best opportunity to gauge the
relevance of the various possible evolutionary scenarios. This also allows to
sketch the post-main sequence evolution of massive stars, for which
observations of Wolf-Rayet stars give essential clues. Recent supernova
discoveries due to the current boost in transient searches allow tentative
mappings of progenitor models with supernova types, including pair instability
supernovae and gamma-ray bursts.
A new method is presented for calculating the time evolution of spherically
symmetric Type Ia Supernova in the post-explosion phase, enabling light curves
and spectra to be simulated in a physically self-consistent way.
The commonly exploited radiative equilibrium, that is in essence a /gas
energy balance/ condition, is unsuitable for this purpose for important
physical and numerical reasons. Firstly, the RE depends on the heating and
cooling rates of the gas by the radiation field, two quantities that almost
completely cancel and are very difficult to calculate accurately. Secondly, the
internal energy of the gas is only a tiny fraction of the total energy in the
system (the vast majority of the energy resides in the radiation field), so
that the vast majority of the energy is neglected in solving for the energy
balance.
The method presented in this paper, based on the /radiation energy balance/,
addresses the bulk of the energy, does not depend on the heating/cooling rates,
guarantees an accurate run of the bolometric luminosity over time while
bringing the gas temperatures into consistence with the radiation field.
We have implemented the method in the stellar atmosphere code PHOENIX and
applied it to the classical W7 model. The results illustrate the importance of
each of the four physical contributions to the energy balance as a function of
time. The simulated spectra and light curves for W7 show good resemblance to
the observations, which demonstrates what can be done using PHOENIX with the
REB method.
We define and put at disposal SOAP, Spot Oscillation And Planet, a software tool that simulates the effect of stellar spots and plages on radial velocimetry and photometry. This paper describes the tool release and provides instructions for its use. We present detailed tests to assess its performance and to validate the suitability of the code with previous computations and real data. We characterize the variations of the radial velocity, line bisector, and photometric amplitude as a function of the main variables: projected stellar rotational velocity, filling factor of the spot, resolution of the spectrograph, linear limb-darkening coefficient, latitude of the spot, and inclination of the star. Finally, we model the spot distributions on the active stars HD166435, TW Hya and HD189733 that reproduces the observations. We show that the software is remarkably fast allowing several evolutions in its capabilities that could be done to study the next challenges in the exoplanetary field connected with the stellar variability.
Strategic Plan for Astronomy in the Netherlands 2011 - 2020, written by the Netherlands Committee for Astronomy (NCA), on behalf of the excellence research school in astronomy NOVA, (combining the university astronomy institutes of the universities of Amsterdam, Groningen, Leiden and Nijmegen), the NWO division of Physical Sciences, the Netherlands Institute for Radio Astronomy ASTRON and the Netherlands Institute for Space Research SRON. The Strategic plan outlines the scientific priorities for Dutch astronomy in the next decade; the instrumentation effort required to address these priorities, and the connection between astronomical instrumentation and technology development and fundamental technological R&D; the financial contours needed to realise the priorities; and the role of Dutch astronomy in education and outreach. The Strategic Plan also includes a retrospective on the achievements since the last Strategic Plan (2000) and a forward look beyond 2020.
Bulges can be classified into classical and pseudobulges; the former are considered to be end products of galactic mergers and the latter to form via secular evolution of galactic disks. Observationally, bulges of disk galaxies are mostly pseudobulges, including the Milky Way's. We here show, by using self-consistent cosmological simulations of galaxy formation, that the formation of pseudobulges of Milky Way-sized disk galaxies has mostly completed before disk formation; thus the main channel of pseudobulge formation is not secular evolution of disks. Our pseudobulges form by rapid gas supply at high-redshift and their progenitors would be observed as high-redshift disks.
We report the discovery via radial velocity of a short-period (P = 2.430420 \pm 0.000006 days) companion to the F-type main sequence star TYC 2930-00872-1. A long-term trend in the radial velocities indicates the presence of a tertiary stellar companion with $P > 2000$ days. High-resolution spectroscopy of the host star yields T_eff = 6427 +/- 33 K, log(g) = 4.52 +/- 0.14, and [Fe/H]=-0.04 +/- 0.05. These parameters, combined with the broad-band spectral energy distribution and parallax, allow us to infer a mass and radius of the host star of M_1=1.21 +/- 0.08 M_\odot and R_1=1.09_{-0.13}^{+0.15} R_\odot. We are able to exclude transits of the inner companion with high confidence. The host star's spectrum exhibits clear Ca H and K core emission indicating stellar activity, but a lack of photometric variability and small v*sin(I) suggest the primary's spin axis is oriented in a pole-on configuration. The rotational period of the primary from an activity-rotation relation matches the orbital period of the inner companion to within 1.5 \sigma, suggesting they are tidally locked. If the inner companion's orbital angular momentum vector is aligned with the stellar spin axis, as expected through tidal evolution, then it has a stellar mass of M_2 ~ 0.3-0.4 M_\odot. Direct imaging limits the existence of stellar companions to projected separations < 30 AU. No set of spectral lines and no significant flux contribution to the spectral energy distribution from either companion are detected, which places individual upper mass limits of M < 1.0 M_\odot, provided they are not stellar remnants. If the tertiary is not a stellar remnant, then it likely has a mass of ~0.5-0.6 M_\odot, and its orbit is likely significantly inclined from that of the secondary, suggesting that the Kozai-Lidov mechanism may have driven the dynamical evolution of this system.
We present parallax and proper motion measurements, near-infrared spectra, and WISE photometry for the low surface gravity L5gamma dwarf 2MASSJ035523.51+113337.4 (2M0355). We use these data to evaluate photometric, spectral, and kinematic signatures of youth. We confirm low-gravity spectral morphology and find a strong resemblance to the sharp triangular shaped H-band spectrum of the ~10 Myr planetary-mass object 2MASSJ1207b. We find that 2M0355 is underluminous compared to a normal field L5 dwarf in the optical and MKO J,H, and K bands and transitions to being overluminous from 3-12 microns indicating that enhanced photospheric dust shifts flux to longer wavelengths for young, low-gravity objects, creating a red spectral energy distribution. Investigating the near-infrared color magnitude diagram for brown dwarfs confirms that 2M0355 is redder and underluminous compared to the known brown dwarf population, similar to the peculiarities of directly imaged exoplanets 2MASSJ1207b and HR8799bcd. We calculate UVW space velocities and find that while the motion of 2M0355 is consistent with young disk objects (< 2-3 Gyr) we can not confirm its association with the youngest nearby associations (e.g. Beta Pictoris, AB Doradus, TW Hydrae). The birthplace, current moving group membership, and constrained age (hence mass) for 2M0355 remain unknown.
The FU Orionis (FUor) or EX Orionis (EXor) phenomenon has attracted increasing attention in recent years and is now accepted as a crucial element in the early evolution of low-mass stars. FUor and EXor eruptions of young stellar objects (YSOs) are caused by strongly enhanced accretion from the surrounding disk. FUors display optical outbursts of $\sim$ 4 mag or more and last for several decades, whereas EXors show smaller outbursts ($\Delta$m $\sim$ 2 - 3 mag) that last from a few months to a few years and may occur repeatedly. Therefore, FUor/EXor eruptions represent a rare but very important phenomenon in early stellar evolution, during which a young low-mass YSO brightens by up to several optical magnitudes. Hence, long-term observations of this class of eruptive variable are important to design theoretical models of low-mass star formation. In this paper, we present recent results from our long-term monitoring observations of three rare types of eruptive young variables with the 2-m Himalayan {\it Chandra} Telescope (HCT) and the 2-m IUCAA Girawali Observatory (IGO) telescope.
Context: The majority of studies on stressed 3D magnetic null points consider
magnetic reconnection driven by an external perturbation, but the formation of
a genuine current sheet equilibrium remains poorly understood. This problem has
been considered more extensively in two-dimensions, but lacks a generalization
into 3D fields.
Aims: 3D magnetic nulls are more complex than 2D nulls and the field can take
a greater range of magnetic geometries local to the null. Here, we focus on one
type and consider the dynamical non-resistive relaxation of 3D spiral nulls
with initial spine-aligned current. We aim to provide a valid
magnetohydrostatic equilibrium, and describe the electric current accumulations
in various cases, involving a finite plasma pressure.
Methods: A full MHD code is used, with the resistivity set to zero so that
reconnection is not allowed, to run a series of experiments in which a
perturbed spiral 3D null point is allowed to relax towards an equilibrium, via
real, viscous damping forces. Changes to the initial plasma pressure and other
magnetic parameters are investigated systematically.
Results: For the axi-symmetric case, the evolution of the field and the
plasma is such that it concentrates the current density in two cone-shaped
regions along the spine, thus concentrating the twist of the magnetic field
around the spine, leaving a radial configuration in the fan plane. The plasma
pressure redistributes in order to maintain the current density accumulations.
However, it is found that changes in the initial plasma pressure do not modify
the final state significantly. In the cases where the initial magnetic field is
not axi-symmetric, a infinite-time singularity of current perpendicular to the
fan is found at the location of the null.
We use images taken with the infrared channel of the Wide Field Camera 3 on the Hubble Space Telescope (HST) to study the multiple main sequences (MSs) of NGC 2808. Below the turn off, the red, the middle, and the blue MS, previously detected from visual-band photometry, are visible over an interval of about 3.5 F160W magnitudes. The three MSs merge together at the level of the MS bend. At fainter magnitudes, the MS again splits into two components containing ~65% and ~35% of stars, with the most-populated MS being the bluest one. Theoretical isochrones suggest that the latter is connected to the red MS discovered in the optical color-magnitude diagram (CMD), and hence corresponds to the first stellar generation, having primordial helium and enhanced carbon and oxygen abundances. The less-populated MS in the faint part of the near-IR CMD is helium-rich and poor in carbon and oxygen, and it can be associated with the middle and the blue MS of the optical CMD. The finding that the photometric signature of abundance anticorrelation are also present in fully convective MS stars reinforces the inference that they have a primordial origin.
In this work we investigate and parameterize the amount and angular distribution of Cherenkov photons, which are generated by low-energy secondary particles (typically $\lesssim 500 $\,MeV), which accompany a muon track in water or ice. These secondary particles originate from small energy loss processes. We investigate the contributions of the different energy loss processes as a function of the muon energy and the maximum transferred energy. For the calculation of the angular distribution we have developed a generic transformation method, which allows us to derive the angular distribution of Cherenkov photons for an arbitrary distribution of track directions and their velocities.
The association of Type Ic supernovae (SNe) with long-duration gamma-ray bursts (GRB) is well established. GRB 120422A was a low-redshift (z=0.283) event that allowed an extensive ground-based observational campaign to monitor the light curve of the associated SN 2012bz. We obtained a series of photometric and spectroscopic observations of SN 2012bz associated with the long-duration GRB 120422A using the 3.6-m TNG and the 8.2-m VLT telescopes during the time interval between 4 and 36 days after the burst. We characterized the optical light curve of SN 2012bz and compared its shape with other GRB/SNe. Peak brightness was reached ~18 days after the burst, corresponding to ~14 days in the rest-frame. A general resemblance between the spectra of SN 2012bz and SN 1998bw at similar epochs is noticed, but the spectra are too noisy for detailed analysis. The shape and maximum of the bolometric light curve (M ~ -18.7) are very similar to those of other known GRB/SNe, suggesting comparable explosion conditions and parameters. GRB 120422A may lie slightly above the 2\sigma confidence region of the Epeak-Eiso relation.
We present BVR observations of DK CVn from 2007 and 2008. We analysed the BVR light curves of the system and obtained the system's parameters. Using the `q-search' method, we measured the mass ratio of the system (q) as 0.55. Taking the temperature of the primary component as 4040K, the temperature of the secondary was found to be 3123K. Several flares were detected, and the distributions of flare equivalent duration versus flare total duration were modelled using the One-Phase Exponential Association Function for these flares. The parameters of the model demonstrated that the flares are the same as those detected from UV Ceti stars. We also demonstrate that the variation at out-of-eclipse must be caused by some cool spot(s) on one of the components. The star is found to show two active longitudes in which the spots are mainly formed. Consequently, this study reveals that DK CVn should be a chromospherically active binary star.
Taking into account results obtained from light-curve analysis and out-of-eclipse analyses, we discuss the nature of GSC 02038-00293 and also its magnetic activity behaviour. We obtained light curves of the system during observing seasons 2007, 2008 and 2011. We obtained its secondary minimum clearly in I-band observations in 2008 for the first time. Analysing this light curve, we found the physical parameters of the components. The light-curve analysis indicates that the possible mass ratio of the system is 0.35. We obtained the remaining V-band light curves, extracting the eclipses. We modelled these remaining curves using the spotmodel program and found possible spot configurations of the magnetically active component for each observing season. The models demonstrated that there are two active longitudes for the active component. The models reveal that both active longitudes migrate in the direction of decreasing longitude. We also examined the light curves in out-of-eclipse phases with respect to minimum and maximum brightness, amplitude, etc. The amplitude of the curves during out-of-eclipse phases varies in a sinusoidal way with a period of ~8.9yr the mean brightness of the system is dramatically decreasing. The phases of the deeper minimum during out-of-eclipse periods exhibit a migration toward decreasing phase.
The solar nebula is thought to have undergone a number of episodes of FU Orionis outbursts during its early evolution. We present here the first calculations of the trajectories of particles in a marginally gravitationally unstable solar nebula during an FU Orionis outburst, which show that 0.1 to 10 cm-sized particles traverse radial distances of 10 AU or more, inward and outward, in less than 200 yrs, exposing the particles to temperatures from $\sim$ 60 K to $\sim$ 1500 K. Such trajectories can thus account for the discovery of refractory particles in comets. Refractory particles should acquire Wark-Lovering-like rims as they leave the highest temperature regions of the disk, and these rims should have significant variations in their stable oxygen isotope ratios. Particles are likely to be heavily modified or destroyed if they pass within 1 AU of the Sun, and so are only likely to survive if they formed in the final few FU Orionis outbursts, or were transported to the outer reaches of the solar system. Calcium, aluminum-rich inclusions (CAIs) from primitive meteorites are the oldest known solar system objects and have a very narrow age range. Most CAIs may have formed at the end of the FU Orionis outbursts phase, with an age range reflecting the period between the last few outbursts.
Neutron stars enable us to study both the highest densities and the highest magnetic fields in the known Universe. In this article I review what can be learned about such fundamental physics using magnetar bursts. Both the instability mechanisms that trigger the bursts, and the subsequent dynamical and radiative response of the star, can be used to explore stellar and magnetospheric structure and composition.
We present a photometric and spectroscopic study of the unique isolated nearby dSph galaxy KKR25. The galaxy was resolved into stars with HST/WFPC2 including old red giant branch and red clump. We have constructed a model of the resolved stellar populations and measured the star formation rate and metallicity as function of time. The main star formation activity period occurred about 12.6 to 13.7 Gyr ago. These stars are mostly metal-poor, with a mean metallicity [Fe/H]\sim -1 to -1.6 dex. About 60 per cent of the total stellar mass was formed during this event. There are indications of intermediate age star formation in KKR25 between 1 and 4 Gyr with no significant signs of metal enrichment for these stars. Long-slit spectroscopy was carried out using the Russian 6-m telescope of the integrated starlight and bright individual objects in the galaxy. We have discovered a planetary nebula (PN) in KKR25. This is the first known PN in a dwarf spheroidal galaxy outside the Local Group. We have measured its oxygen abundance 12+log(O/H)=7.60+-0.07 dex and a radial velocity Vh=-79 km/s. We have analysed the stellar density distribution in the galaxy body. The galaxy has an exponential surface brightness profile with a central light depression. We discuss the evolutionary status of KKR25, which belongs to a rare class of very isolated dwarf galaxies with spheroidal morphology.
A Chern-Simons coupling of a new scalar field to electromagnetism may give rise to cosmological birefringence, a rotation of the linear polarization of electromagnetic waves as they propagate over cosmological distances. Prior work has sought this rotation, assuming the rotation angle to be uniform across the sky, by looking for the parity-violating TB and EB correlations a uniform rotation produces in the CMB temperature/polarization. However, if the scalar field that gives rise to cosmological birefringence has spatial fluctuations, then the rotation angle may vary across the sky. Here we search for direction-dependent cosmological birefringence in the WMAP-7 data. We report the first CMB constraint on the rotation-angle power spectrum for multipoles between L = 0 and L = 512. We also obtain a 68% confidence-level upper limit of 0.8 degrees on the square root of the quadrupole of a scale-invariant rotation-angle power spectrum.
In the presence of cosmic chiral asymmetry, chiral-vorticity and chiral-magnetic effects can play an important role in the generation and evolution of magnetic fields in the early universe. We include these chiral effects in the magnetic field equations and find solutions under simplifying assumptions. Our numerical and analytical results show the presence of an attractor solution in which chiral effects produce a strong, narrow, Gaussian peak in the magnetic spectrum and the magnetic field becomes maximally helical. The peak in the spectrum shifts to longer length scales and becomes sharper with evolution. We also find that the dynamics may become non-linear for certain parameters, pointing to the necessity of a more complete analysis.
We present Keck/LRIS spectra of over 200 galaxies with well-determined redshifts between 0.4 and 1.4. We combine new measurements of near-ultraviolet, low-ionization absorption lines with previously measured masses, luminosities, colors, and star formation rates to describe the demographics and properties of galactic flows. Among star-forming galaxies with blue colors, we find a net blueshift of the Fe II absorption greater than 200 km/s (100 km/s) towards 2.5% (20%) of the galaxies. The fraction of spectra with blueshifts decreases significantly among galaxies with specific star formation rates less than roughly 0.8 Gyr^{-1} and does not vary significantly with stellar mass, color, or luminosity. The insensitivity of the blueshifted fraction to galaxy properties favors collimated outflows, and in this context we demonstrate how the solid angle of the outflow declines with increasing outflow velocity. We also detect enriched infall towards 3-6% of the galaxies, apparently observed at an optimal viewing angle. At least 3 (1) of the 9 infalling streams have a large cross section and velocities commensurate with an extended disk (satellite galaxy). We explain the strong dependence of the Mg II absorption equivalent width on stellar mass, B-band luminosity, and U-B color by resonance emission partially filling in the intrinsic absorption troughs; emission filling can also explain the significant differences often observed between the shape of the Mg II line profile and the absorption troughs of those Fe II transitions that decay primarily by fluorescence. This study provides a new quantitative understanding of gas flows between galaxies and the circumgalactic medium over a critical period in galaxy evolution.
It is clear that optical selection effects have distorted the "true" GRB redshift distribution to its presently observed biased distribution. We constrain a statistically optimal model that implies GRB host galaxy dust extinction could account for up to 40% of missing optical afterglows and redshifts in $z = 0-3$, but the bias is negligible at very high-$z$. The limiting sensitivity of the telescopes, and the time to acquire spectroscopic/photometric redshifts, are significant sources of bias for the very high-$z$ sample. We caution on constraining star formation rate and luminosity evolution using the GRB redshift distribution without accounting for these selection effects.
Recently published crater statistics on the small asteroids 25143 Itokawa and 433 Eros show a significant depletion of craters below approx. 100 m in diameter. Possible mechanisms that were brought up to explain this lack of craters were seismic crater erasure and self armoring of a coarse, boulder covered asteroid surface. While seismic shaking has been studied in this context, the concept of armoring lacks a deeper inspection and an experimental ground truth. We therefore present cratering experiments of glass bead projectiles impacting into granular glass bead targets, where the grain sizes of projectile and target are in a similar range. The impact velocities are in the range of 200 to 300 m/s. We find that craters become fainter and irregular shaped as soon as the target grains are larger than the projectile sizes and that granular craters rarely form when the size ratio between projectile and target grain is around 1:10 or smaller. In that case, we observe a formation of a strength determined crater in the first struck target grain instead. We present a simple model based on the transfer of momentum from the projectile to this first target grain, which is capable to explain our results with only a single free parameter, which is moreover well determined by previous experiments. Based on estimates of typical projectile size and boulder size on Itokawa and Eros, given that our results are representative also for km/s impact velocities, armoring should play an important role for their evolution.
We examine the properties and evolution of a simulated polar disc galaxy. This galaxy is comprised of two orthogonal discs, one of which contains old stars (old stellar disc), and the other, containing both younger stars and the cold gas (polar disc) of the galaxy. By exploring the shape of the inner region of the dark matter halo, we are able to confirm that the halo shape is a oblate ellipsoid flattened in the direction of the polar disc. We also note that there is a twist in the shape profile, where the innermost 3 kpc of the halo flattens in the direction perpendicular to the old disc, and then aligns with the polar disc out until the virial radius. This result is then compared to the halo shape inferred from the circular velocities of the two discs. We also use the temporal information of the simulation to track the system's evolution, and identify the processes which give rise to this unusual galaxy type. We confirm the proposal that the polar disc galaxy is the result of the last major merger, where the angular moment of the interaction is orthogonal to the angle of the infalling gas. This merger is followed by the resumption of coherent gas infall. We emphasise that the disc is rapidly restored after the major merger and that after this event the galaxy begins to tilt. A significant proportion of the infalling gas comes from filaments. This infalling gas from the filament gives the gas its angular momentum, and, in the case of the polar disc galaxy, the direction of the gas filament does not change before or after the last major merger.
We present an observational study of the Type IIn supernovae (SNe IIn) 2005ip and 2006jd. Broad-band UV, optical and near-IR photometry, and visual-wavelength spectroscopy of SN 2005ip complement and extend upon published observations to 6.5 years past discovery. Our observations of SN 2006jd extend from UV to mid-infrared wavelengths, and like SN 2005ip, are compared to reported X-ray measurements to understand the nature of the progenitor. Both objects display a number of similarities with the 1988Z-like subclass of SN IIn including: (i) remarkably similar early- and late-phase optical spectra, (ii) a variety of high ionization coronal lines, (iii) long-duration optical and near-IR emission and, (iv) evidence of cold and warm dust components. However, diversity is apparent including an unprecedented late-time r-band excess in SN 2006jd.The observed differences are attributed to differences between the mass-loss history of the progenitor stars. We conclude that the progenitor of SN 2006jd likely experienced a significant mass-loss event during its pre-SN evolution akin to the great 19th century eruption of \eta Carinae. Contrarily, as advocated by Smith et al. (2009), we find the circumstellar environment of SN 2005ip to be more consistent with a clumpy wind progenitor.
The Sh2-294 HII region ionized by a single B0V star features several infrared excess sources, a photodissociation region, and also a group of reddened stars at its border. The star formation scenario in the region seems to be quite complex. In this paper, we present follow-up results of Sh2-294 HII region at 3.6, 4.5, 5.8, and 8.0 microns observed with the Spitzer Space Telescope Infrared Array Camera (IRAC), coupled with H2 (2.12 microns) observation, to characterize the young population of the region and to understand its star formation history. We identified 36 young stellar object (YSO, Class I, Class II and Class I/II) candidates using IRAC color-color diagrams. It is found that Class I sources are preferentially located at the outskirts of the HII region and associated with enhanced H2 emission; none of them are located near the central cluster. Combining the optical to mid-infrared (MIR) photometry of the YSO candidates and using the spectral energy distribution fitting models, we constrained stellar parameters and the evolutionary status of 33 YSO candidates. Most of them are interpreted by the model as low-mass (< 4 solar masses) YSOs; however, we also detected a massive YSO (~9 solar masses) of Class I nature, embedded in a cloud of visual extinction of ~24 mag. Present analysis suggests that the Class I sources are indeed younger population of the region relative to Class II sources (age ~ 4.5 x 10^6 yr). We suggest that the majority of the Class I sources, including the massive YSOs, are second-generation stars of the region whose formation is possibly induced by the expansion of the HII region powered by a ~ 4 x 10^6 yr B0 main-sequence star.
The exoplanets known as hot Jupiters---Jupiter-sized planets with periods less than 10 days---likely are relics of dynamical processes that shape all planetary system architectures. Socrates et al. (2012) argued that high eccentricity migration (HEM) mechanisms proposed for situating these close-in planets should produce an observable population of highly eccentric proto hot Jupiters that have not yet tidally circularized. HEM should also create failed hot Jupiters, with periapses just beyond the influence of fast circularization. Using the technique we previously presented for measuring eccentricities from photometry (the "photoeccentric effect"), we are distilling a collection of eccentric proto and failed hot Jupiters from the Kepler Objects of Interest (KOI). Here we present the first, KOI-1474.01, which has a long orbital period (69.7340 days) and a large eccentricity e = 0.81 +0.10/-0.07, skirting the proto hot Jupiter boundary. Combining Keplerphotometry, ground-based spectroscopy, and stellar evolution models, we characterize host KOI-1474 as a rapidly-rotating F-star. Statistical arguments allow us to validate the transiting planet. KOI-1474.01 also exhibits transit timing variations of order an hour. We explore characteristics of the third-body perturber, which is possibly the "smoking-gun" cause of KOI-1474.01's large eccentricity. Using the host-star's rotation period, radius, and projected rotational velocity, we find KOI-1474.01's orbit is marginally consistent with aligned with the stellar spin axis, although a reanalysis is warranted with future additional data. Finally, we discuss how the number and existence of proto hot Jupiters will not only demonstrate that hot Jupiters migrate via HEM, but also shed light on the typical timescale for the mechanism.
We present the H-alpha imaging data and flux measurements for 30 dwarf galaxies in the Local volume. The H-alpha fluxes are used to derive the galaxy star formation rate, SFR. The sample of observed galaxies is characterized by the following parameters: the median distance of 7.5 Mpc, the median blue absolute magnitude of -14.8 mag, and median SFR of -2.0 dex. Two dSph members of the Local Group: Cetus and Leo IV do not show signs of star formation on the rate of -5.4 dex and -7.0 dex, respectively. The BCD galaxy ESO 553-46 has one of the highest specific SFR among the Local volume galaxies.
We derive the Boltzmann equation in the synchronous gauge for massive neutrinos with a deformed dispersion relation. Combining the 7-year WMAP data with lower-redshift measurements of the expansion rate, we give constraints on the deformation parameter and find that the deformation parameter is strong degenerate with the physical dark matter density instead of the neutrino mass. Our results show that there is no evidence for Lorentz invariant violation in the neutrino sector. The ongoing Planck experiment could provide improved constraints on the deformation parameter.
(Shortened) GRB080319B, with an isotropic energy E_{iso}=1.32x10^{54}erg, and GRB050904, with E_{iso}=1.04x10^{54}erg, offer the possibility of studying the spectral properties of the prompt radiation of two of the most energetic Gamma-Ray Bursts (GRBs). This allows us to probe the validity of the fireshell model for GRBs beyond 10^{54}erg, well outside the energy range where it has been successfully tested up to now (10^{49}-10^{53}erg). We find that in the low energy region, the prompt emission spectra observed by Swift BAT reveals more power than theoretically predicted. The opportunities offered by these observations to improve the fireshell model are outlined. One of the distinguishing features of the fireshell model is that it relates the observed spectra to the spectrum in the comoving frame of the fireshell. Originally, a fully radiative condition and a comoving thermal spectrum were adopted. An additional power-law in the comoving thermal spectrum is required [...] in the fireshell model for GRBs 080319B and 050904. A new phenomenological parameter \alpha is correspondingly introduced in the model. We perform numerical simulations of the prompt emission in the Swift BAT bandpass by assuming different values of \alpha [...]. We compare them with the GRB080319B and GRB050904 observed time-resolved spectra, as well as with their time-integrated spectra and light curves. Although GRB080319B and GRB050904 are at very different redshifts (z=0.937 and z=6.29 respectively), a value of \alpha=-1.8 leads for both of them to a good agreement between the numerical simulations and the observed BAT light curves, time-resolved and time-integrated spectra. Such a modified spectrum is also consistent with the observations of previously analyzed less energetic GRBs and reasons for this additional agreement are given. Perspectives for future low energy missions are outlined.
It is believed that turbulence may have a significant impact on star formation and the dynamics and evolution of the molecular clouds in which this occurs. It is also known that non-ideal magnetohydrodynamic effects influence the nature of this turbulence. We present the results of a numerical study of 4-fluid MHD turbulence in which the dynamics of electrons, ions, charged dust grains and neutrals and their interactions are followed. The parameters describing the fluid being simulated are based directly on observations of molecular clouds. We find that the velocity and magnetic field power spectra are strongly influenced by multifluid effects on length-scales at least as large as 0.05 pc. The PDFs of the various species in the system are all found to be close to log-normal, with charged species having a slightly less platykurtic (flattened) distribution than the neutrals. We find that the introduction of multifluid effects does not significantly alter the structure functions of the centroid velocity increment.
We report results of a systematic study of the broad band (2--2000 keV) time resolved prompt emission spectra of a sample of gamma-ray bursts (GRBs) detected with both Wide Field Cameras on board the \sax\ satellite and the \batse\ experiment on board CGRO. In this first paper, we study the time-resolved dependence of the intrinsic peak energy $E_{p,i}$ of the $E F(E)$ spectrum on the corresponding isotropic bolometric luminosity $L_{\rm iso}$. The $E_{p,i}$--$L_{\rm iso}$ relation or the equivalent relation between $E_{p,i}$ and the bolometric released energy $E_{iso}$, derived using the time averaged spectra of long GRBs with known redshift, is well established, but its physical origin is still a subject of discussion. In addition, some authors maintain that these relations are the result of instrumental selection effects. We find that not only a relation between the measured peak energy $E_p$ and the corresponding energy flux, but also a strong $E_{p,i}$ versus $L_{\rm iso}$ correlation are found within each burst and merging together the time resolved data points from different GRBs. We do not expect significant instrumental selection effects that can affect the obtained results, apart from the fact that the GRBs in our sample are sufficiently bright to perform a time-resolved spectroscopy and that they have known redshift. If the fundamental physical process that gives rise to the GRB phenomenon does not depend on its brightness, we conclude that the found $E_{p,i}$ versus $L_{\rm iso}$ correlation within each GRB is intrinsic to the emission process, and that the correlations discovered by Amati et al. and Yonetoku et al. are likely not the result of selection effects. We also discuss the properties of the correlations found.
By phenomenologically describing the high-redshift star formation history, i.e., $\dot{\rho}_{*}(z)\propto[(1+z)/4.5]^{-\alpha}$, and semi-analytically calculating the fractions of high-redshift Pop I/II and Pop III stars, we investigate the contributions from both high-redshfit Pop I/II and Pop III stars to the observed near-infrared ($3 \mu\rm m<\lambda<5 \mu m$) excess in the cosmic infrared background emission. In order to account for the observational level of the near-infrared excess, the power-law index $\alpha$ of the assumed star formation history is constrained to within the range of $0\lesssim\alpha\lesssim1$. Such a constraint is obtained under the condition that the viral temperature of dark matter halos belongs to the range of $500 {\rm K}\leq T_{\rm vir}\leq10^4$ K.
With the large sample of young gamma-ray pulsars discovered by the Fermi Large Area Telescope (LAT), population synthesis has become a powerful tool for comparing their collective properties with model predictions. We synthesised a pulsar population based on a radio emission model and four gamma-ray gap models (Polar Cap, Slot Gap, Outer Gap, and One Pole Caustic), and we scaled it to the surveys by applying gamma-ray and radio visibility criteria. The power and the wide beams from the outer gaps can easily account for the number of Fermi detections in 2 years of observations. For the wide slot-gap beams, an increase by a factor of ~10 of the predicted luminosity is required and is conceivable for offset polar caps. The narrow polar-cap beams contribute at most a handful of LAT pulsars. Standard distributions in birth location and pulsar spin-down power (Edot), as well as distributions skewed to more abundant and more energetic births in the inner Galaxy, fail to reproduce the LAT findings: all models under-predict the number of LAT pulsars with high Edot, and they cannot explain the high probability of detecting both the radio and gamma-ray beams at high Edot. The beaming factor remains close to 1.0 over 4 decades in Edot evolution for the slot gap whereas it significantly decreases with increasing age for the outer gaps. The evolution of the enhanced slot-gap luminosity with Edot is compatible with the large dispersion seen in the LAT data. The stronger evolution predicted for the outer gap, which is linked to the polar cap heating by the return current, is apparently not supported by the LAT data. The LAT sample therefore provides a fresh perspective on the early evolution, in luminosity and beam width, of the gamma-ray emission from young pulsars, calling for thin and more luminous gaps.
We present a short review of GRB studies performed for many years by Ioffe Institute experiments onboard a number of space missions. The first breakthrough in the studies of GRB was made possible by four Konus experiments carried out by the Ioffe Institute onboard the Venera 11-14 deep space missions from 1978 to 1983. A new important stage of our research is associated with the joint Russian-American experiment with the Russian Konus scientific instrument onboard the U.S. Wind spacecraft which has been successfully operating since its launch in November 1994. The Konus-Wind experiment has made an impressive number of important GRB observations and other astrophysical discoveries, due to the advantages of its design and its interplanetary location. We also briefly discuss future GRB experiments of the Ioffe Institute.
The effects of acoustic wave absorption, mode conversion and transmission by a sunspot on the helioseismic inferences are widely discussed, but yet accounting for them has proved difficult for lack of a consistent framework within helioseismic modelling. Here, following a discussion of problems and issues that the near-surface magnetohydrodynamics hosts through a complex interplay of radiative transfer, measurement issues, and MHD wave processes, I present some possibilities entirely from observational analyses based on imaging spectropolarimetry. In particular, I present some results on wave evolution as a function of observation height and inclination of magnetic field to the vertical, derived from a high-cadence imaging spectropolarimetric observation of a sunspot and its surroundings using the instrument IBIS (NSO/Sac Peak, USA). These observations were made in magnetically sensitive (Fe I 6173 A) and insensitive (Fe I 7090 A) upper photospheric absorption lines. Wave travel time contributions from within the photospheric layers of a sunspot estimated here would then need to be removed from the inversion modelling procedure, that does not have the provision to account for them.
The Large Magellanic Cloud (LMC) is rich in supernova remnants (SNRs) which can be investigated in detail with radio, optical and X-ray observations. SNR J0453-6829 is an X-ray and radio-bright remnant in the LMC, within which previous studies revealed the presence of a pulsar wind nebula (PWN), making it one of the most interesting SNRs in the Local Group of galaxies. We study the emission of SNR J0453-6829 to improve our understanding of its morphology, spectrum, and thus the emission mechanisms in the shell and the PWN of the remnant. We obtained new radio data with the Australia Telescope Compact Array and analysed archival XMM-Newton observations of SNR J0453-6829. We studied the morphology of SNR J0453-6829 from radio, optical and X-ray images and investigated the energy spectra in the different parts of the remnant. Our radio results confirm that this LMC SNR hosts a typical PWN. The prominent central core of the PWN exhibits a radio spectral index alpha_Core of -0.04+/-0.04, while in the rest of the SNR shell the spectral slope is somewhat steeper with alpha_Shell = -0.43+/-0.01. We detect regions with a mean polarisation of P ~ (12+/-4)% at 6 cm and (9+/-2)% at 3 cm. The full remnant is of roughly circular shape with dimensions of (31+/-1) pc x (29+/-1) pc. The spectral analysis of the XMM-Newton EPIC and RGS spectra allowed us to derive physical parameters for the SNR. Somewhat depending on the spectral model, we obtain for the remnant a shock temperature of around 0.2 keV and estimate the dynamical age to 12000-15000 years. Using a Sedov model we further derive an electron density in the X-ray emitting material of 1.56 cm^-3, typical for LMC remnants, a large swept-up mass of 830 solar masses, and an explosion energy of 7.6 x 10^50 erg. These parameters indicate a well evolved SNR with an X-ray spectrum dominated by emission from the swept-up material.
In this paper we describe and evaluate new spectral line polarisation observations obtained with the goal of mapping the surfaces of magnetic Ap stars in great detail. One hundred complete or partial Stokes IQUV sequences, corresponding to 297 individual polarised spectra, have been obtained for 7 bright Ap stars using the ESPaDOnS and NARVAL spectropolarimeters. The targets span a range of mass from approximately 1.8 to 3.4 solar mass, a range of rotation period from 2.56 to 6.80 days, and a range of maximum longitudinal magnetic field strength from 0.3 to over 4 kG. For 3 of the 7 stars, we have obtained dense phase coverage sampling the entire rotational cycle. These datasets are suitable for immediate magnetic and chemical abundance surface mapping using Magnetic Doppler Imaging (MDI). For the 4 remaining stars, partial phase coverage has been obtained, and additional observations will be required in order to map the surfaces of these stars. The median signal-to-noise ratio of the reduced observations is over 700 per 1.8 km\s pixel. Spectra of all stars show Stokes V Zeeman signatures in essentially all individual lines, and most stars show clear Stokes QU signatures in many individual spectral lines. The observations provide a vastly improved data set compared to previous generations of observations in terms of signal-to-noise ratio, resolving power and measurement uncertainties. Measurement of the longitudinal magnetic field demonstrates that the data are internally consistent within computed uncertainties typically at the 50 to 100 sigma level. Data are also shown to be in excellent agreement with published observations and in qualitative agreement with the predictions of published surface structure models. This study establishes the performance and stability of the ESPaDOnS and NARVAL high-resolution spectropolarimeters during the period 2006-2010.
The late afterglow of gamma-ray burst is believed to be due to progressive deceleration of the forward shock wave driven by the gamma-ray burst ejecta propagating in the interstellar medium. We study the dynamic effect of interstellar turbulence on shock wave propagation. It is shown that the shock wave decelerates more quickly than previously assumed without the turbulence. As an observational consequence, an earlier jet break will appear in the light curve of the forward shock wave. The scatter of the jet-corrected energy release for gamma-ray burst, inferred from the jet-break, may be partly due to the physical uncertainties in the turbulence/shock wave interaction. This uncertainties also exist in two shell collisions in the well-known internal shock model proposed for gamma-ray burst prompt emission. The large scatters of known luminosity relations of gamma-ray burst may be intrinsic and thus gamma-ray burst is not a good standard candle. We also discuss the other implications.
The 100 square degree FCRAO CO survey of the Taurus molecular cloud provides an excellent opportunity to undertake an unbiased survey of a large, nearby, molecular cloud complex for molecular outflow activity. Our study provides information on the extent, energetics and frequency of outflows in this region, which are then used to assess the impact of outflows on the parent molecular cloud. The search identified 20 outflows in the Taurus region, 8 of which were previously unknown. Both $^{12}$CO and $^{13}$CO data cubes from the Taurus molecular map were used, and dynamical properties of the outflows are derived. Even for previously known outflows, our large-scale maps indicate that many of the outflows are much larger than previously suspected, with eight of the flows (40%) being more than a parsec long. The mass, momentum and kinetic energy from the 20 outflows are compared to the repository of turbulent energy in Taurus. Comparing the energy deposition rate from outflows to the dissipation rate of turbulence, we conclude that outflows by themselves cannot sustain the observed turbulence seen in the entire cloud. However, when the impact of outflows is studied in selected regions of Taurus, it is seen that locally, outflows can provide a significant source of turbulence and feedback. Five of the eight newly discovered outflows have no known associated stellar source, indicating that they may be embedded Class 0 sources. In Taurus, 30% of Class I sources and 12% of Flat spectrum sources from the Spitzer YSO catalogue have outflows, while 75% of known Class 0 objects have outflows. Overall, the paucity of outflows in Taurus compared to the embedded population of Class I and Flat Spectrum YSOs indicate that molecular outflows are a short-lived stage marking the youngest phase of protostellar life.
The foreshock region of a CME shock front, where shock accelerated electrons
form a beam population in the otherwise quiescent plasma is generally assumed
to be the source region of type II radio bursts. Nonlinear wave interaction of
electrostatic waves excited by the beamed electrons are the prime candidates
for the radio waves' emission.
To address the question whether a single, or two counterpropagating beam
populations are a requirement for this process, we have conducted 2.5D particle
in cell simulations using the fully relativistic ACRONYM code.
Results show indications of three wave interaction leading to electromagnetic
emission at the fundamental and harmonic frequency for the two-beam case. For
the single-beam case, no such signatures were detectable.
The growth and saturation of Buneman-type instabilities is examined with a particle-in-cell (PIC) simulation for parameters that are representative for the foreshock region of fast supernova remnant (SNR) shocks. A dense ion beam and the electrons correspond to the upstream plasma and a fast ion beam to the shock-reflected ions. The purpose of the 2D simulation is to identify the nonlinear saturation mechanisms, the electron heating and potential secondary instabilities that arise from anisotropic electron heating and result in the growth of magnetic fields. We confirm that the instabilities between both ion beams and the electrons saturate by the formation of phase space holes by the beam-aligned modes. The slower oblique modes accelerate some electrons, but they can not heat up the electrons significantly before they are trapped by the faster beam-aligned modes. Two circular electron velocity distributions develop, which are centred around the velocity of each ion beam. They develop due to the scattering of the electrons by the electrostatic wave potentials. The growth of magnetic fields is observed, but their amplitude remains low.
The detections of both X-ray and radio emission from the cluster G1 in M31 have provided strong support for existing dynamical evidence for an intermediate mass black hole (IMBH) of mass 1.8 +/- 0.5 x 10^4 solar masses at the cluster center. However, given the relatively low significance and astrometric accuracy of the radio detection, and the non-simultaneity of the X-ray and radio measurements, this identification required further confirmation. Here we present deep, high angular resolution, strictly simultaneous X-ray and radio observations of G1. While the X-ray emission (L_X = 1.74^{+0.53}_{-0.44} x 10^{36} (d/750 kpc)^2 erg/s in the 0.5-10 keV band) remained fully consistent with previous observations, we detected no radio emission from the cluster center down to a 3-sigma upper limit of 4.7 microJy/beam. Our favored explanation for the previous radio detection is flaring activity from a black hole low mass X-ray binary (LMXB). We performed a new regression of the Fundamental Plane of black hole activity, valid for determining black hole mass from radio and X-ray observations of sub-Eddington black holes, finding log M_{BH} = (1.638 +/- 0.070)log L_R - (1.136 +/- 0.077)log L_X - (6.863 +/- 0.790), with an empirically-determined uncertainty of 0.44 dex. This constrains the mass of the X-ray source in G1, if a black hole, to be <9700 solar masses at 95% confidence, suggesting that it is a persistent LMXB. This annuls what was previously the most convincing evidence from radiation for an IMBH in the Local Group, though the evidence for an IMBH in G1 from velocity dispersion measurements remains unaffected by these results.
We present results from a spectroscopic survey of the dwarf spheroidal And XXII and the two extended clusters EC1 and EC2. These three objects are candidate satellites of the Triangulum galaxy, M33, which itself is likely a satellite of M31. We use the DEep Imaging Multi-Object Spectrograph mounted on the Keck-II telescope to derive radial velocities for candidate member stars of these objects and thereby identify the stars that are most likely actual members. Ten probable stellar members are found for AndXXII. We obtain an upper limit of sigma_v < 6.0 km s-1 for the velocity dispersion of AndXXII, [Fe/H] ~ -1.8 for its metallicity, and 255pc for the Plummer radius of its projected density profile. We construct a colour magnitude diagram for AndXXII and identify both the red giant branch and the horizontal branch. The position of the latter is used to derive a heliocentric distance to And XXII of 853 pm 26 kpc. The combination of the radial velocity, distance, and angular position of AndXXII indicates that it is a strong candidate for being the first known satellite of M33 and one of the very few examples of a galactic satellite of a satellite. N-body simulations imply that this conclusion is unchanged even if M31 and M33 had a strong encounter in the past few Gyr. We test the hypothesis that the extended clusters highlight tidally stripped galaxies by searching for an excess cloud of halo-like stars in their vicinity. We find such a cloud for the case of EC1 but not EC2. The three objects imply a dynamical mass for M33 that is consistent with previous estimates.
Scalar-tensor theories are constrained with lunar laser ranging and supernovae data at low redshift. This allows to find some constraints on the scalar field independently on the form of its potential once the gravitation function is specified. We apply these results to some well known scalar-tensor theories showing that they agreed with the LCDM model at 1 sigma.
We present a simple model for the non-thermal emission from the historical supernova remnant SN 1006. We constrain the synchrotron parameters of the model with archival radio and hard X-ray data. Our stationary emission model includes two populations of electrons, which is justified by multi-frequency images of the object. From the set of parameters that predict the correct synchrotron flux we select those which are able to account, either partly or entirely, for the gamma-ray emission of the source as seen by HESS. We use the results from this model as well as the latest constraints imposed by the Fermi observatory and conclude that the TeV emission cannot be accounted for by neutral pion decay produced by high-energy cosmic rays with a single "soft" power-law distribution (i.e., with a particle index greater than 2 or so).
We explore a set of single-point chemical models to study the fundamental chemical aspects of episodic accretion in low-mass embedded protostars. Our goal is twofold: (1) to understand how the repeated heating and cooling of the envelope affects the abundances of CO and related species; and (2) to identify chemical tracers that can be used as a novel probe of the timescales and other physical aspects of episodic accretion. We develop a set of single-point models that serve as a general prescription for how the chemical composition of a protostellar envelope is altered by episodic accretion. The main effect of each accretion burst is to drive CO ice off the grains in part of the envelope. The duration of the subsequent quiescent stage (before the next burst hits) is similar to or shorter than the freeze-out timescale of CO, allowing the chemical effects of a burst to linger long after the burst has ended. We predict that the resulting excess of gas-phase CO can be observed with single-dish or interferometer facilities as evidence of an accretion burst in the past 10^3 - 10^4 yr.
We present deep Giant Metrewave Radio Telescope (GMRT) radio observations at 240, 330 and 610 MHz of the complex radio source at the center of the NGC1407 galaxy group. Previous GMRT observations at 240 MHz revealed faint, diffuse emission enclosing the central twin-jet radio galaxy. This has been interpreted as an indication of two possible radio outbursts occurring at different times. Both the inner double and diffuse component are detected in the new GMRT images at high levels of significance. Combining the GMRT observations with archival Very Large Array data at 1.4 and 4.9 GHz, we derive the total spectrum of both components. The inner double has a spectral index \alpha=0.7, typical for active, extended radio galaxies, whereas the spectrum of the large-scale emission is very steep, with \alpha=1.8 between 240 MHz and 1.4 GHz. The radiative age of the large-scale component is very long, ~300 Myr, compared to ~30 Myr estimated for the central double, confirming that the diffuse component was generated during a former cycle of activity of the central galaxy. The current activity have so far released an energy which is nearly one order of magnitude lower than that associated with the former outburst. The group X-ray emission in the Chandra and XMM-Newton images and extended radio emission show a similar swept-back morphology. We speculate that the two structures are both affected by the motion of the group core, perhaps due to the core sloshing in response to a recent encounter with the nearby elliptical galaxy NGC1400.
Sylvia is a triple asteroid system located in the main belt. We report new adaptive optics observations of this system that extend the baseline of existing astrometric observations to a decade. We present the first fully dynamical 3-body model for this system by fitting to all available astrometric measurements. This model simultaneously fits for individual masses, orbits, and primary oblateness. We find that Sylvia is composed of a dominant central mass surrounded by two satellites orbiting at 706.5 +/- 2.5 km and 1357 +/- 4.0 km, i.e., about 5 and nearly 10 primary radii. We derive individual masses of 1.484 -0.014/+0.016 x 10^19 kg for the primary (corresponding to a density of 1.29 +/- 0.39 g cm^-3), 7.33 -2.3/+4.7 x 10^14 kg for the inner satellite, and 9.32 -8.3/+20.7 x 10^14 kg for the outer satellite. The oblateness of the primary induces substantial precession and the J_2 value can be constrained to the range of 0.0985-0.1. The orbits of the satellites are relatively circular with eccentricities less than 0.04. The spin axis of the primary body and the orbital poles of both satellites are all aligned within about two degrees of each other, indicating a nearly coplanar configuration and suggestive of satellite formation in or near the equatorial plane of the primary. We also investigate the past orbital evolution of the system by simulating the effects of a recent passage through 3:1 mean-motion eccentricity-type resonances. In some scenarios this allow us to place constraints on interior structure and past eccentricities.
DEMs have been used to experimental studying the temporal evolution of the March maximum of fluxes of near-Earth daemons. It is shown that part of objects from near-Earth almost circular heliocentric orbits (NEACHOs), from which a rather intense flux proceeds during only about four weeks, forms in the second half of March the population in geocentric Earth-surface-crossing orbits (GESCOs). The resistance of the Earth's matter results in that GESCO objects sink into the Earth's interior, so that the GESCO population nearly disappears by the end of April.
We present radially resolved spectroscopy of 8 early-type galaxies in Abell~262, measuring rotation, velocity dispersion, $H_3$ and $H_4$ coefficients along three axes, and line-strength index profiles of Mg, Fe and H$\beta$. Ionized-gas velocity and velocity dispersion is included for 6 galaxies. We derive dynamical mass-to-light ratios and dark matter densities from orbit-based dynamical models, complemented by the galaxies' ages, metallicities, and $\alpha$-elements abundances. Four galaxies have significant dark matter with halos about 10 times denser than in spirals of the same stellar mass. Using dark matter densities and cosmological simulations, assembly redshifts $\zdm\approx 1-3$, which we found earlier for Coma. The dynamical mass following the light is larger than expected for a Kroupa stellar IMF, especially in galaxies with high velocity dispersion $\sigeff$ inside the effective radius $\reff$. This could indicate a `massive' IMF in massive galaxies. Alternatively, some dark matter in massive galaxies could follow the light closely. Combining with our comparison sample of Coma early-types, we now have 5 of 24 galaxies where (1) mass follows light to $1-3\,\reff$, (2) the dynamical mass-to-light ratio {of all the mass that follows the light is large ($\approx\,8-10$ in the Kron-Cousins $R$ band), (3) the dark matter fraction is negligible to $1-3\,\reff$. Unless the IMF in these galaxies is particularly `massive' and somehow coupled to the dark matter content, there seems a significant degeneracy between luminous and dark matter in some early-type galaxies. The role of violent relaxation is briefly discussed.
The dynamical evolution of dense stellar systems is simulated using a
two-dimensional Fokker-Planck method, with the goal of providing a model for
the formation of supermassive stars which could serve as seed objects for the
supermassive black holes of quasars. This work follows and expands on earlier
1-D studies of spherical clusters of main-sequence stars. The 2-D approach
allows for the study of rotating systems, as would be expected due to
cosmological tidal torquing; other physical effects included are collisional
mergers of stars and a bulk stellar bar perturbation in the gravitational
potential. The 3 Myr main-sequence lifetime for large stars provides an upper
limit on simulation times. Two general classes of initial systems are studied:
Plummer spheres, which represent stellar clusters, and \gamma=0 spheres, which
model galactic spheroids.
At the initial densities of the modeled systems, mass segregation and runaway
stellar collisions alone are insufficient to induce core collapse within the
lifetime limit if no bar perturbation is included. However, core collapse is
not a requirement for the formation of a massive object: the choice of stellar
initial mass function is found to play a crucial role. When using an IMF
similar to that observed for dense stellar clusters the simulations show that
the stellar system forms massive (250M_\odot) objects by collisional mergers;
in almost all such cases the presence of a stellar bar allows for sufficient
additional outward transport of angular momentum that a core-collapse state is
reached with corresponding further increase in the rate of formation of massive
objects. In contrast, simulations using an IMF similar to that observed for
field stars in general (which is weighted more towards lower masses) produce no
massive objects, and reach core collapse only for initial models which
represent the highest-density galactic spheriods.
We describe mixing scalar particles and Majorana fermions using Closed-Time-Path methods. From the Kadanoff-Baym equations, we obtain the charge asymmetry, that is generated from decays and inverse decays of the mixing particles. Within one single formalism, we thereby treat Leptogenesis from oscillations and recover as well the standard results for the asymmetry in Resonant Leptogenesis, which apply when the oscillation frequency is much larger than the decay rate. Analytic solutions for two mixing neutral particles in a constant-temperature background illustrate our results qualitatively. We also perform the modification of the kinetic equations that is necessary in order to take account of the expansion of the Universe and the washout of the asymmetry.
Leptogenesis may be induced by the mixing of extra Higgs doublets with experimentally accessible masses. This mechanism relies on diagrammatic cuts that are kinematically forbidden in the vacuum but contribute at finite temperature. A resonant enhancement of the asymmetry occurs generically provided the dimensionless Yukawa and self-interactions are suppressed compared to those of the Standard Model Higgs field. This is in contrast to typical scenarios of Resonant Leptogenesis, where the asymmetry is enhanced by imposing a degeneracy of singlet neutrino masses.
An unification model with the characteristic flavor structures and the TeV scale $U(1)_{B-L}$ symmetry is suggested to solve the fermion masses and flavor mixings as well as the baryon asymmetry and dark matter. The model excellently fits all the current experimental data. All of the new results and predictions are promising to be test in future experiments.
We have evaluated the optical and electrical properties of a far-infrared (IR) transparent electrode for extrinsic germanium (Ge) photoconductors at 4 K, which was fabricated by molecular beam epitaxy (MBE). As a far-IR transparent electrode, an aluminum (Al)-doped Ge layer is formed at well-optimized doping concentration and layer thickness in terms of the three requirements: high far-IR transmittance, low resistivity, and excellent ohmic contact. The Al-doped Ge layer has the far-IR transmittance of >95 % within the wavelength range of 40--200 microns, while low resistivity (~5 ohm-cm) and ohmic contact are ensured at 4 K. We demonstrate the applicability of the MBE technology in fabricating the far-IR transparent electrode satisfying the above requirements.
For Leptogenesis based on the type-I seesaw mechanism, we present a systematic calculation of lepton-number violating and purely flavoured asymmetries within nonequilibrium Quantum Field Theory. We show that sterile neutrinos with non-degenerate masses in the GeV range can explain the baryon asymmetry of the Universe via flavoured Leptogenesis. This is possible due to the interplay of thermal and flavour effects. Our approach clarifies the relation between Leptogenesis from the oscillations of sterile neutrinos and the more commonly studied scenarios from decays and inverse decays. We explain why lower mass bounds for non-degenerate sterile neutrinos derived for Leptogenesis from out-of-equilibrium decays do not apply to flavoured Leptogenesis with GeV-scale neutrinos.
Here is reported in situ observation of energetic electrons (~100-500 keV) associated with magnetic reconnection in the solar wind by the ACE and Wind spacecraft. The properties of this magnetic cloud driving reconnection and the associated energetic electron acceleration problem are discussed. Further analyses indicate that the electric field acceleration and Fermi type mechanism are two fundamental elements in the electron acceleration processes and the trapping effect of the specific magnetic field configuration maintains the acceleration status that increases the totally gained energy.
The Magnetic cloud boundary layer (BL) is a dynamic region formed by the interaction of the magnetic cloud (MC) and the ambient solar wind. In the present study, we comparatively investigate the proton and electron mean flux variations in the BL, in the interplanetary reconnection exhaust (RE) and across the MC-driven shock by using the Wind 3DP and MFI data from 1995 to 2006. In general, the proton flux has higher increments at lower energy bands compared with the ambient solar wind. Inside the BL, the core electron flux increases quasi-isotropically and the increments decrease monotonously with energy from ~30% (at 18 eV) to ~10% (at 70 eV); the suprathermal electron flux usually increases in either parallel or antiparallel direction; the correlation coefficient of electron flux variations in parallel and antiparallel directions changes sharply from ~0.8 below 70 eV to ~0 above 70 eV. Similar results are also found for RE. However, different phenomena are found across the shock where the electron flux variations first increase and then decrease with a peak increment (>200%) near 100 eV. The correlation coefficient of electron flux variations in parallel and antiparallel directions is always around 0.8. The similar behavior of flux variations in BL and RE suggests that reconnection may commonly occur in BL. Our work also implies that the strong energy dependence and direction selectivity of electron flux variations, which are previously thought to have no enough relevance to magnetic reconnection, could be considered as an important signature of solar wind reconnection in the statistical point of view.
Large-scale arrays of Microwave Kinetic Inductance Detectors (MKIDs) are attractive candidates for use in imaging instruments for next generation submillimeter-wave telescopes such as CCAT. We have designed and fabricated tightly packed ~250-pixel MKID arrays using lumped-element resonators etched from a thin layer of superconducting TiNx deposited on a silicon substrate. The high pixel packing density in our initial design resulted in large microwave crosstalk due to electromagnetic coupling between the resonators. Our second design eliminates this problem by adding a grounding shield and using a double-wound geometry for the meander inductor to allow conductors with opposite polarity to be in close proximity. In addition, the resonator frequencies are distributed in a checkerboard pattern across the array. We present details for the two resonator and array designs and describe a circuit model for the full array that predicts the distribution of resonator frequencies and the crosstalk level. We also show results from a new experimental technique that conveniently measures crosstalk without the need for an optical setup. Our results reveal an improvement in crosstalk from 57% in the initial design down to \leq 2% in the second design. The general procedure and design guidelines in this work are applicable to future large arrays employing microwave resonators.
It has recently been shown that the graviton can consistently gain a constant mass without introducing the Boulware-Deser ghost. We propose a gravity model where the graviton mass is set by a scalar field and prove that this model is free of the Boulware-Deser ghost by analyzing its constraint system and showing that two constraints arise. We also initiate the study of the model's cosmic background evolution and tentatively discuss possible cosmological implications of this model. In particular, we consider a simple scenario where the scalar field setting the graviton mass is identified with the inflaton and the graviton mass evolves from a high to a low energy scale, giving rise to the current cosmic acceleration.
Canonical methods allow the derivation of effective gravitational actions from the behavior of space-time deformations reflecting general covariance. With quantum effects, the deformations and correspondingly the effective actions change, revealing dynamical implications of quantum corrections. A new systematic way of expanding these actions is introduced showing as a first result that inverse-triad corrections of loop quantum gravity simplify the asymptotic dynamics near a spacelike collapse singularity. By generic quantum effects, the singularity is removed.
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In this study, a new method is presented to classify flares derived from the photoelectric photometry of UV Ceti type stars. This method is based on statistical analyses using an independent samples t-test. The data used in analyses were obtained from four flare stars observed between 2004 and 2007. The total number of flares obtained in the observations of AD Leo, EV Lac, EQ Peg, and V1054 Oph is 321 in the standard Johnson U band. As a result flares can be separated into two types, slow and fast, depending on the ratio of flare decay time to flare rise time. The ratio is below 3.5 for all slow flares, while it is above 3.5 for all fast flares. Also, according to the independent samples t-test, there is a difference of about 157 s between equivalent durations of slow and fast flares. In addition, there are significant differences between amplitudes and rise times of slow and fast flares.
In this study, we considered stellar spots, stellar flares, and also the relation between these two magnetic proccesses that take place on UV Cet stars. In addition, the hypothesis about slow flares described by Gurzadyan (1986 Ap&SS, 125, 127) was investigated. All of these discussions were based on the results of three years of observations of UV Cet-type stars: AD Leo, EV Lac, V1005 Ori, EQ Peg, and V1054 Oph. First of all, the results show that stellar spot activity occurs on the stellar surface of EV Lac, V1005 Ori, and EQ Peg, while AD Leo does not show any short-term variability and V1054 Oph does not exhibit any variability. We report on new ephemerides for EV Lac, V1005 Ori, and EQ Peg, obtained from time-series analyses. The phases, computed at intervals of 0.10 phase length, where the mean flare occurence rates to obtain maximum amplitude; also, the phases of rotational modulation were compared in order to investigate whether there is any longitudinal relation between stellar flares and spots. Although the results show that flare events are related with spotted areas on stellar surfaces during some of the observing seasons, we did not find any clear correlation among them. Finally, it was tested whether slow flares are fast flares occurring on the opposite side of the stars according to the direction of the observers, as mentioned in a hypothesis developed by <A >Gurzadyan (1986)</A>. The flare occurence rates reveal that both slow and fast flares can occur in any rotational phases. The flare occurence rates of both fast and slow flares vary in the same way along the longitudes for all program stars. These results are not expected based on the case mentioned in the hypothesis.
Taking into account results obtained from models and from statistical analyses of obtained parameters, we discuss flare activity levels and flare characteristics of five UV Ceti stars. We present the parameters of unpublished flares detected over two years of observations of V1005 Ori. We compare parameters of the U-band flares detected over several seasons of observations of AD Leo, EV Lac, EQ Peg, V1054 Oph, and V1005 Ori. Flare frequencies calculated for all program stars and maximum energy levels of the flares are compared, and we consider which is the most correct parameter as an indicator of flare activity levels. Using the One Phase Exponential Association function, the distributions of flare equivalent duration versus flare total duration are modeled for each program star. We use the Independent Samples t-Test in the statistical analyses of the parameters obtained from the models. The results reveal some properties of flare processes occurring on the surfaces of UV Ceti type stars. (1) Flare energies cannot be higher than a specific value regardless of the length of the flare total duration. This must be a saturation level for white-light flares occurring in flare processes observed in the U band. Thus, for the first time it is shown that white-light flares have a saturation in a specific energy range. (2) The span values, which are the difference between the equivalent durations of flares with the shortest and longest total durations, are almost equal for each star. (3) The half-life values, minimum flare durations for saturation, increase toward the later spectral types.
Statistically analyzing Johnson UBVR observations of V1285 Aql during the three observing seasons, both activity level and behavior of the star are discussed in respect to obtained results. We also discuss the out-of-flare variation due to rotational modulation. Eighty-three flares were detected in the U-band observations of season 2006 . First, depending on statistical analyses using the independent samples t-test, the flares were divided into two classes as the fast and the slow flares. According to the results of the test, there is a difference of about 73 s between the flare-equivalent durations of slow and fast flares. The difference should be the difference mentioned in the theoretical models. Second, using the one-phase exponential association function, the distribution of the flare-equivalent durations versus the flare total durations was modeled. Analyzing the model, some parameters such as plateau, half-life values, mean average of the flare-equivalent durations, maximum flare rise, and total duration times are derived. The plateau value, which is an indicator of the saturation level of white-light flares, was derived as 2.421{\pm}0.058 s in this model, while half-life is computed as 201 s. Analyses showed that observed maximum value of flare total duration is 4641 s, while observed maximum flare rise time is 1817 s. According to these results, although computed energies of the flares occurring on the surface of V1285 Aql are generally lower than those of other stars, the length of its flaring loop can be higher than those of more active stars.
We present EXOFAST, a fast, robust suite of routines written in IDL which is designed to fit exoplanetary transits and radial velocity variations simultaneously or separately, and characterize the parameter uncertainties and covariances with a Differential Evolution Markov Chain Monte Carlo method. We describe how our code self-consistently incorporates both data sets to simultaneously derive stellar parameters along with the transit and RV parameters, resulting in consistent, but tighter constraints on an example fit of the discovery data of HAT-P-3b that is well-mixed in under two minutes on a standard desktop computer. We describe in detail how our code works and outline ways in which the code can be extended to include additional effects or generalized for the characterization of other data sets -- including non-planetary data sets. We discuss the pros and cons of several common ways to parameterize eccentricity, highlight a subtle mistake in the implementation of MCMC that would bias the inferred eccentricity of intrinsically circular orbits to significantly non-zero results, discuss a problem with IDL's built-in random number generator in its application to large MCMC fits, and derive a method to analytically fit the linear and quadratic limb darkening coefficients of a planetary transit. Finally, we explain how we achieved improved accuracy and over a factor of 100 improvement in the execution time of the transit model calculation. Our entire source code, along with an easy-to-use online interface for several basic features of our transit and radial velocity fitting, are available online at this http URL
We provide new, high-resolution A(Ks) extinction maps of the heavily reddened Galactic midplane based on the Rayleigh-Jeans Color Excess ("RJCE") method. RJCE determines star-by-star reddening based on a combination of near- and mid-infrared photometry. The new RJCE-generated maps have 2 x 2 arcmin pixels and span some of the most severely extinguished regions of the Galaxy -- those covered with Spitzer+IRAC imaging by the GLIMPSE-I, -II, -3D, and Vela-Carina surveys, from 256<l<65 deg and, in general, for |b| <= 1-1.5 deg (extending up to |b|<=4 deg in the bulge). Using RJCE extinction measurements, we generate dereddened color-magnitude diagrams and, in turn, create maps based on main sequence, red clump, and red giant star tracers, each probing different distances and thereby providing coarse three-dimensional information on the relative placement of dust cloud structures. The maps generated from red giant stars, which reach to ~18-20 kpc, probe beyond most of the Milky Way extinction in most directions and provide close to a "total Galactic extinction" map -- at minimum they provide high angular resolution maps of lower limits on A(Ks). Because these maps are generated directly from measurements of reddening by the very dust being mapped, rather than inferred on the basis of some less direct means, they are likely the most accurate to date for charting in detail the highly patchy differential extinction in the Galactic midplane. We provide downloadable FITS files and an IDL tool for retrieving extinction values for any line of sight within our mapped regions.
Bayesian model selection methods provide a self-consistent probabilistic framework to test the validity of competing scenarios given a set of data. We present a case study application to strong gravitational lens parametric models. To this end we confront a lens power-law potential against the presence of external shear on a sample of double-image quasars using measurements of the image positions and time-delays. Our goal is to select a homogeneous lens subsample suitable for cosmological parameter inference. In the case of B1600+434, SBS 1520+530 and SDSS J1650+4251 the Bayes' factor analysis favors a simple power-law model description with high statistical significance. The combined likelihood data analysis of such systems gives the Hubble constant H_0 = 72^{+22}_{-40} km s^{-1}Mpc^{-1} for a flat \LambdaCDM cosmology having marginalized over the lens model parameters, the cosmic matter density and consistently propagated the observational errors on the angular position of the images. The next generation of cosmic structure surveys will provide larger lens datasets and the method described here can be particularly useful to select homogeneous lens subsamples adapt to perform unbiased cosmological parameter inference.
Aims: Grain growth has been suggested as one possible explanation for the
diminished dust optical depths in the inner regions of protoplanetary
"transition" disks. In this work, we directly test this hypothesis in the
context of current models of grain growth and transport.
Methods: A set of dust evolution models with different disk shapes, masses,
turbulence parameters, and drift efficiencies is combined with radiative
transfer calculations in order to derive theoretical spectral energy
distributions (SEDs) and images.
Results: We find that grain growth and transport effects can indeed produce
dips in the infrared SED, as typically found in observations of transition
disks. Our models achieve the necessary reduction of mass in small dust by
producing larger grains, yet not large enough to be fragmenting efficiently.
However, this population of large grains is still detectable at millimeter
wavelengths. Even if perfect sticking is assumed and radial drift is neglected,
a large population of dust grains is left behind because the time scales on
which they are swept up by the larger grains are too long. This mechanism thus
fails to reproduce the large emission cavities observed in recent
millimeter-wave interferometric images of accreting transition disks.
The linewidth (sigma) - size (R) relationship has been extensively measured and analysed, in both the local ISM and in nearby normal galaxies. Generally, a power-law describes the relationship well with an index ranging from 0.2-0.6, now referred to as one of "Larson's Relationships." The nature of turbulence and star formation is considered to be intimately related to these relationships, so evaluating the sigma-R correlations in various environments is important for developing a comprehensive understanding of the ISM. We measure the sigma-R relationship in the Central Molecular Zone (CMZ) of the Galactic Centre using spectral line observations of the high density tracers N2H+, HCN, H13CN, and HCO+. We use dendrograms, which map the hierarchical nature of the position-position-velocity (PPV) data, to compute sigma and R of contiguous structures. The dispersions range from ~2-30 km/s in structures spanning sizes 2-40 pc, respectively. By performing Bayesian inference, we show that a power-law with exponent 0.3-1.1 can reasonably describe the sigma-R trend. We demonstrate that the derived sigma-R relationship is independent of the locations in the PPV dataset where sigma and R are measured. The uniformity in the sigma-R relationship suggests turbulence in the CMZ is driven on the large scales beyond >30 pc. We compare the CMZ sigma-R relationship to that measured in the Galactic molecular cloud Perseus. The exponents between the two systems are similar, suggestive of a connection between the turbulent properties within a cloud to its ambient medium. Yet, the velocity dispersion in the CMZ is systematically higher, resulting in a coefficient that is nearly five times larger. The systematic enhancement of turbulent velocities may be due to the combined effects of increased star formation activity, larger densities, and higher pressures relative to the local ISM.
This paper examines star formation (SF) in relatively massive, primarily early-type galaxies (ETGs) at z~0.1. A sample is drawn from bulge-dominated GALEX/SDSS galaxies on the optical red sequence with strong UV excess and yet quiescent SDSS spectra. High-resolution far-UV imaging of 27 such ETGs using HST ACS/SBC reveals structured UV morphology in 93% of the sample, consistent with low-level ongoing SF (~0.5 Ms/yr). In 3/4 of the sample the SF is extended on galaxy scales (25-75 kpc), while the rest contains smaller (5-15 kpc) SF patches in the vicinity of an ETG - presumably gas-rich satellites being disrupted. Optical imaging reveals that all ETGs with galaxy-scale SF in our sample have old stellar disks (mostly S0 type). None is classified as a true elliptical. In our sample, galaxy-scale SF takes the form of UV rings of varying sizes and morphologies. For the majority of such objects we conclude that the gas needed to fuel current SF has been accreted from the IGM, probably in a prolonged, quasi-static manner, leading in some cases to additional disk buildup. The remaining ETGs with galaxy-scale SF have UV and optical morphologies consistent with minor merger-driven SF or with the final stages of SF in fading spirals. Our analysis excludes that all recent SF on the red sequence resulted from gas-rich mergers. We find further evidence that galaxy-scale SF is almost exclusively an S0 phenomenon (~20% S0s have SF) by examining the overall optically red SDSS ETGs. Conclusion is that significant number of field S0s maintain or resume low-level SF because the preventive feedback is not in place or is intermittent. True ellipticals, on the other hand, stay entirely quiescent even in the field.
A small fraction of the atomic-cooling halos assembling at z<15 may form out of minihalos that never experienced any prior star formation, and could in principle host small galaxies of chemically unenriched stars. Since the prospects of detecting isolated population III stars appear bleak even with the upcoming James Webb Space Telescope (JWST), these population III galaxies may offer one of the best probes of population III stars in the foreseeable future. By projecting the results from population III galaxy simulations through cluster magnification maps, we predict the fluxes and surface number densities of pop III galaxy galaxies as a function of their typical star formation efficiency. We argue that a small number of lensed population III galaxies in principle could turn up at z=7-10 in the ongoing Hubble Space Telescope survey CLASH, which covers a total of 25 low-redshift galaxy clusters.
The Zurich Environmental Study (ZENS) is designed to compare the dependence of z=0 galaxy structural and stellar populations diagnostics at constant stellar mass on four measures of the environment: the mass of the host group halos; the projected distance from the center of the halo; the rank of galaxies as central or satellites; and the filamentary LSS density on which the groups reside. The complete ZENS sample contains 1630 galaxies in 141~10^{12.5-14}M_sun 2PIGG groups at z~0.06. We outline the survey motivation and describe novel approaches to quantify the environments of galaxies. We introduce a set of self-consistency checks to define the group centers and to rank galaxies as centrals or satellites, and describe an Nth-nearest-neighbor approach to determine the LSS density field using groups as tracers. We publish the ZENS catalogue of galaxy and group properties, which combines the environmental diagnostics presented here with structural and SED measurements described in subsequent papers. In a suite of follow-up articles we investigate which measures of environment most strongly affect the galaxy properties. In this paper, we highlight the following: a) For ~40% of <10^13.5 M_sun groups there is no self-consistent identification of a central galaxy and ~10-20% of groups may be dynamically young systems; b) Properties of central galaxies in the relaxed and unrelaxed groups are similar indicating that central galaxies are not regulated by their environment but exclusively by their stellar mass; c) Satellites with M>10^10 M_sun in relaxed and unrelaxed groups, as well as centrals, have similar size, color and star formation rate distributions, but at lower galaxy masses satellites are ~0.1mag bluer in unrelaxed groups. This indicates that physical processes occurring in dynamically-relaxed group halos are important to quench star formation in low mass satellites.[Abridged]
Kaiser redshift-space distortion formula describes well the clustering of galaxies in redshift surveys on small scales, but there are numerous additional terms that arise on large scales. Some of these terms can be described using Newtonian dynamics and have been discussed in the literature, while the others require proper general relativistic description that was only recently developed. Accounting for these terms in galaxy clustering is the first step toward tests of general relativity on horizon scales. The effects can be classified as two terms that represent the velocity and the gravitational potential contributions. Their amplitude is determined by effects such as the volume and luminosity distance fluctuation effects and the time evolution of galaxy number density and Hubble parameter. We compare the Newtonian approximation often used in the redshift-space distortion literature to the fully general relativistic equation, and show that Newtonian approximation accounts for most of the terms contributing to velocity effect. We perform a Fisher matrix analysis of detectability of these terms and show that in a single tracer survey they are completely undetectable. To detect these terms one must resort to the recently developed methods to reduce sampling variance and shot noise. We show that in an all-sky galaxy redshift survey at low redshift the velocity term can be measured at a few sigma if one can utilize halos of mass M>10^12 Msun (this can increase to 10-sigma or more in some more optimistic scenarios), while the gravitational potential term itself can only be marginally detected. We also demonstrate that the general relativistic effect is not degenerate with the primordial non-Gaussian signature in galaxy bias, and the ability to detect primordial non-Gaussianity is little compromised.
In this paper we discuss the contribution of different astrophysical sources to the ionization of neutral hydrogen at different redshifts. We critically revise the arguments in favour/against a substantial contribution of Active Galactic Nuclei (AGNs) and/or Lyman Break Galaxies (LBGs) to the reionization of the Universe at z>5. We consider extrapolations of the high-z QSO and LBG luminosity functions and their redshift evolution as well as indirect constraints on the space density of lower luminosity Active Galactic Nuclei based on the galaxy stellar mass function. Since the hypothesis of a reionization due to LBGs alone requires a significant contribution of faint dwarf galaxies and a LyC photon escape fraction (f_esc) of the order of ~20%, in tension with present observational constraints, we examine under which hypothesis AGNs and LBGs may provide a combined relevant contribution to the reionization. We show that a relatively steep faint-end of the AGN luminosity function, consistent with present constraints, provides a relevant (although sub-dominant) contribution, thus allowing us to recover the required ionizing photon rates with f_esc~5% up to z~7. At higher redshifts, we test the case for a luminosity-dependent f_esc scenario and we conclude that, if the observed LBGs are indeed characterized by very low f_esc, values of the order of f_esc~70% are needed for objects below our detection threshold, for this galaxy population to provide a substantial contribution to reionization. Clearly, the study of the properties of faint sources (both AGNs and LBGs) is crucial.
Collisional ring galaxies are the outcome of nearly axisymmetric high-speed encounters between a disc and an intruder galaxy. We investigate the properties of collisional ring galaxies as a function of the impact parameter, the initial relative velocity and the inclination angle. We employ new adaptive mesh refinement simulations to trace the evolution with time of both stars and gas, taking into account star formation and supernova feedback. Axisymmetric encounters produce circular primary rings followed by smaller secondary rings, while off-centre interactions produce asymmetric rings with displaced nuclei. We propose an analytical treatment of the disc warping induced by an inclination angle greater then zero. The star formation history of our models is mainly influenced by the impact parameter: axisymmetric collisions induce impulsive short-lived starburst episodes, whereas off-centre encounters produce long-lived star formation. We compute synthetic colour maps of our models and we find that rings have a B-V colour typically ~0.2 mag bluer than the inner and outer disc, in agreement with observations.
(shortened) We report the results of an investigation of particle acceleration and electron-positron plasma generation at low altitude in the polar magnetic flux tubes of Rotation Powered Pulsars, when the stellar surface is free to emit whatever charges and currents are demanded by the force-free magnetosphere. We observe novel behavior. a) When the current density is less than the Goldreich-Julian (GJ) value (0<j/j_{GJ}<1), space charge limited acceleration of the current carrying beam is mild, with the full GJ charge density being comprised of the charge density of the beam, co-existing with a cloud of electrically trapped particles with the same sign of charge as the beam. The voltage drops are on the order of mc^2/e, and pair creation is absent. b) When the current density exceeds the GJ value (j/j_{GJ}>1), the system develops high voltage drops, causing emission of gamma rays and intense bursts of pair creation. The bursts exhibit limit cycle behavior, with characteristic time scales somewhat longer than the relativistic fly-by time over distances comparable to the polar cap diameter (microseconds). c) In return current regions, where j/j_{GJ}<0, the system develops similar bursts of pair creation. In cases b) and c), the intermittently generated pairs allow the system to simultaneously carry the magnetospherically prescribed currents and adjust the charge density and average electric field to force-free conditions. We also elucidate the conditions for pair creating beam flow to be steady, finding that such steady flows can occupy only a small fraction of the current density parameter space of the force-free magnetospheric model. The generic polar flow dynamics and pair creation is strongly time dependent. The model has an essential difference from almost all previous quantitative studies, in that we sought the accelerating voltage as a function of the applied current.
Precise stellar radial velocities are used to search for massive (Jupiter masses or higher) exoplanets around the stars of the open cluster M67. We aim to obtain a census of massive exoplanets in a cluster of solar metallicity and age in order to study the dependence of planet formation on stellar mass and to compare in detail the chemical composition of stars with and without planets. This first work presents the sample and the observations, discusses the cluster characteristics and the radial velocity (RV) distribution of the stars, and individuates the most likely planetary host candidates. We observed a total of 88 main-sequence stars, subgiants, and giants all highly probable members of M67, using four telescopes and instrument combinations. We investigate whether exoplanets are present by obtaining radial velocities with precisions as good as 10 m/s. To date, we have performed 680 single observations (Dec. 2011) and a preliminary analysis of data, spanning a period of up to eight years. Although the sample was pre-selected to avoid the inclusion of binaries, we identify 11 previously unknown binary candidates. Eleven stars clearly displayed larger RV variability and these are candidates to host long-term substellar companions. The average RV is also independent of the stellar magnitude and evolutionary status, confirming that the difference in gravitational redshift between giants and dwarfs is almost cancelled by the atmospheric motions. We use the subsample of solar-type stars to derive a precise true RV for this cluster. We finally create a catalog of binaries and use it to clean the color magnitude diagram (CMD). As conclusion, by pushing the search for planets to the faintest possible magnitudes, it is possible to observe solar analogues in open clusters, and we propose 11 candidates to host substellar companions.
We present a detailed study of the infrared spectral energy distribution of the high-redshift radio galaxy MRC 1138-26 at z = 2.156, also known as the Spiderweb Galaxy. By combining photometry from Spitzer, Herschel and LABOCA we fit the rest-frame 5-300 um emission using a two component, starburst and active galactic nucleus (AGN), model. The total infrared (8 - 1000 um) luminosity of this galaxy is (1.97+/-0.28)x10^13 Lsun with (1.17+/-0.27) and (0.79+/-0.09)x10^13 Lsun due to the AGN and starburst components respectively. The high derived AGN accretion rate of \sim20% Eddington, and the measured star formation rate (SFR) of 1390pm150 Msun/yr, suggest that this massive system is in a special phase of rapid central black hole and host galaxy growth, likely caused by a gas rich merger in a dense environment. The accretion rate is sufficient to power both the jets and the previously observed large outflow. The high SFR and strong outflow suggest this galaxy could potentially exhaust its fuel for stellar growth in a few tens of Myr, although the likely merger of the radio galaxy with nearby satellites suggest bursts of star formation may recur again on time scales of several hundreds of Myr. The age of the radio lobes implies the jet started after the current burst of star formation, and therefore we are possibly witnessing the transition from a merger-induced starburst phase to a radio-loud AGN phase. We also note tentative evidence for [CII]158um emission. This paper marks the first results from the Herschel Galaxy Evolution Project (Project HeRGE), a systematic study of the evolutionary state of 71 high redshift, 1 < z < 5.2, radio galaxies.
With the first metal enrichment by Population (Pop) III supernovae (SNe), the formation of the first metal-enriched, Pop II stars becomes possible. In turn, Pop III star formation and early metal enrichment are slowed by the high energy radiation emitted by Pop II stars. Thus, through the SNe and radiation they produce, Populations II and III coevolve in the early Universe, one regulated by the other. We present large (4 Mpc)^3, high resolution cosmological simulations in which we self-consistently model early metal enrichment and the stellar radiation responsible for the destruction of the coolants (H2 and HD) required for Pop III star formation. We find that the molecule-dissociating stellar radiation produced both locally and over cosmological distances reduces the Pop III star formation rate at z > 10 by up to an order of magnitude compared to the case in which this radiation is not included. However, we find that the effect of LW feedback is to enhance the amount of Pop II star formation. We attribute this to the reduced rate at which gas is blown out of dark matter haloes by SNe in the simulation with LW feedback, which results in larger reservoirs for metal-enriched star formation. Even accounting for metal enrichment, molecule-dissociating radiation and the strong suppression of low-mass galaxy formation due to reionization at z < 10, we find that Pop III stars are still formed at a rate of ~ 10^-5 M_sun yr^-1 Mpc^-3 down to z ~ 6. This suggests that the majority of primordial pair-instability SNe that may be uncovered in future surveys will be found at z < 10. We also find that the molecule-dissociating radiation emitted from Pop II stars may destroy H2 molecules at a high enough rate to suppress gas cooling and allow for the formation of supermassive primordial stars which collapse to form ~ 100,000 solar mass black holes.
One of the most promising explanations for the origin of the billion solar mass black holes (BHs) inferred to power quasars at redshifts z > 6 is that supermassive stars (SMSs) with masses > 10,000 solar masses collapse to form the seed BHs from which they grow. Here we review recent theoretical advances which provide support for this scenario. Firstly, given sufficiently high accretion rates of gas into the cores of primordial protogalaxies, it appears that neither the high energy radiation emitted from the stellar surface nor the limited lifetime of SMSs can prevent their growth to masses of up to > 100,000 solar masses. Secondly, recent cosmological simulations suggest that the high fluxes of molecule-dissociating radiation which may be required in order to achieve such high accretion rates may be more common in the early universe than previously thought. We conclude that the majority of supermassive BHs may originate from SMSs at high redshifts.
We study a combined sample of 264 star-forming, 51 composite, and 73 active galaxies using optical spectra from SDSS and mid-infrared (mid-IR) spectra from the Spitzer Infrared Spectrograph. We examine optical and mid-IR spectroscopic diagnostics that probe the amount of star formation and relative energetic contributions from star formation and an active galactic nucleus (AGN). Overall we find good agreement between optical and mid-IR diagnostics. Misclassifications of galaxies based on the SDSS spectra are rare despite the presence of dust obscuration. The luminosity of the [NeII] 12.8 \mu m emission-line is well correlated with the star formation rate (SFR) measured from the SDSS spectra, and this holds for the star forming, composite, and AGN-dominated systems. AGN show a clear excess of [NeIII] 15.6 \mu m emission relative to star forming and composite systems. We find good qualitative agreement between various parameters that probe the relative contributions of the AGN and star formation, including: the mid-IR spectral slope, the ratio of the [NeV] 14.3 \mu m to [NeII] \mu m 12.8 fluxes, the equivalent widths of the 7.7, 11.3, and 17 $\mu m$ PAH features, and the optical "D" parameter which measures the distance a source lies from the locus of star forming galaxies in the optical BPT emission-line diagnostic diagram. We also consider the behavior of the three individual PAH features by examining how their flux ratios depend upon the degree of AGN-dominance. We find that the PAH 11.3 \mu m feature is significantly suppressed in the most AGN-dominated systems.
Supermassive black holes (BH) are powerful sources of energy that are already in place at very early epochs of the Universe (by $z=6$). Using hydrodynamical simulations of the formation of a massive $M_{\rm vir}=5\times 10^{11}\, \rm M_\odot$ halo by $z=6$ (the most massive progenitor of a cluster of $M_{\rm vir}=2\times 10^{15}\, \rm M_\odot$ at $z=0$), we evaluate the impact of Active Galactic Nuclei (AGN) on galaxy mass content, BH self-regulation, and gas distribution inside this massive halo. We find that SN feedback has a marginal influence on the stellar structure, and no influence on the mass distribution on large scales. In contrast, AGN feedback alone is able to significantly alter the stellar-bulge mass content by quenching star formation when the BH is self-regulating, and by depleting the cold gas reservoir in the centre of the galaxy. The growth of the BH proceeds first by a rapid Eddington-limited period fed by direct cold filamentary infall. When the energy delivered by the AGN is sufficiently large to unbind the cold gas of the bulge, the accretion of gas onto the BH is maintained both by smooth gas inflow and clump migration through the galactic disc triggered by merger-induced torques. The feedback from the AGN has also a severe consequence on the baryon mass content within the halo, producing large-scale hot superwinds, able to blow away some of the cold filamentary material from the centre and reduce the baryon fraction by more than 30 per cent within the halo's virial radius. Thus in the very young universe, AGN feedback is likely to be a key process, shaping the properties of the most massive galaxies.
Recent observational surveys of trans-neptunian binary (TNB) systems have dramatically increased the number of known mutual orbits. Our Kozai Cycle Tidal Friction (KCTF) simulations of synthetic trans-neptunian binaries show that tidal dissipation in these systems can completely reshape their original orbits. Specifically, solar torques should have dramatically accelerated the semimajor axis decay and circularization timescales of primordial (or recently excited) TNBs. As a result, our initially random distribution of TNBs in our simulations evolved to have a large population of tight circular orbits. This tight circular population appears for a range of TNO physical properties, though a strong gravitational quadrupole can prevent some from fully circularizing. We introduce a stability parameter to predict the effectiveness of KCTF on a TNB orbit, and show that a number of known TNBs must have a large gravitational quadrupole to be stable.
We explore the possibility that the density profiles of elliptical galaxies and cold dark matter (CDM) halos found in cosmological simulations can be understood in terms of the same physical process, collisionless gravitational collapse. To investigate this, we study a simplified model, the collapse of a perfectly cold Plummer sphere. First, we examine an N-body simulation of this model with particles constrained to purely radial orbits. This results in a final state characterized by a profile slightly steeper than \rho \propto r^{-2} at small radii and behaving as \rho \propto r^{-4} at large radii, which can be understood in terms of simple analytic arguments. Next, we repeat our simulation without the restriction of radial orbits. This results in a shallower inner density profile, like those found in elliptical galaxies and CDM halos. We attribute this change to the radial orbit instability (ROI) and propose a form of the distribution function (DF) motivated by a physical picture of collapse. As evidence of the link between our model and CDM halos, we find that our collapse simulation has a final state with pseudo-phase-space density which scales roughly as \rho/\sigma^3 \propto r^{-1.875}, like that observed in CDM halos from cosmological simulations (Navarro et al. 2010). The velocity anisotropy profile is also qualitatively similar to that found near the centers of these halos. We argue that the discrepancy at large radii (where CDM halos scale as \rho \propto r^{-3}) is due to the presence of the cosmological background or continued infall. This leads us to predict that the outer CDM halo density profile is not "universal," but instead depends on cosmological environment (be it an underdense void or overdense region).
Observed Hot Jupiters exhibit a wide range of physical properties. For a given mass, many planets have inflated radii, while others are surprisingly compact and may harbor large central cores. Motivated by the observational sample, this paper considers possible effects from collisions of smaller rocky planets with gas giant planets. In this scenario, the Jovian planets migrate first and enter into (approximately) 4 day orbits, whereas rocky planets (mass = 0.1-20 that of Earth) migrate later and then encounter the gaseous giants. Previous work indicates that the collision rates are high for such systems. This paper calculates the trajectories of incoming rocky planets as they orbit within the gaseous planets and are subjected to gravitational, frictional, and tidal forces. These collisions always increase the metallicity of the Jovian planets. If the incoming rocky bodies survive tidal destruction and reach the central regions, they provide a means of producing large planetary cores. Both the added metallicity and larger cores act to decrease the radii of the gas giants at fixed mass. The energy released during these collisions provides the Jovian planet with an additional heat source; here we determine the radial layers where kinetic energy of the colliding body is dissipated, including the energy remaining upon impact with the existing core. This process could have long-term effects if the colliding body deposits significant energy deep in the interior, in regions of high opacity. Both Hot Jupiters and newly formed gas giants have inflated radii, large enough to allow incoming rocky planets to survive tidal disruption, enhance the central core mass, and deposit significant energy (in contrast, denser giant planets with the mass and radius of Jupiter are expected to tidally destroy incoming rocky bodies).
We study properties of waves of frequencies above the photospheric acoustic cut-off of $\approx$5.3 mHz, around four active regions, through spatial maps of their power estimated using data from Helioseismic and Magnetic Imager (HMI) and Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO). The wavelength channels 1600 {\AA} and 1700 {\AA} from AIA are now known to capture clear oscillation signals due to helioseismic p modes as well as waves propagating up through to the chromosphere. Here we study in detail, in comparison with HMI Doppler data, properties of the power maps, especially the so called 'acoustic halos' seen around active regions, as a function of wave frequencies, inclination and strength of magnetic field (derived from the vector field observations by HMI) and observation height. We infer possible signatures of (magneto-)acoustic wave refraction from the observation height dependent changes, and hence due to changing magnetic strength and geometry, in the dependences of power maps on the photospheric magnetic quantities. We discuss the implications for theories of p mode absorption and mode conversions by the magnetic field.
We present a new parallel code for computing the dynamical evolution of collisional N-body systems with up to N~10^7 particles. Our code is based on the the H\'enon Monte Carlo method for solving the Fokker-Planck equation, and makes assumptions of spherical symmetry and dynamical equilibrium. The principal algorithmic developments involve optimizing data structures, and the introduction of a parallel random number generation scheme, as well as a parallel sorting algorithm, required to find nearest neighbors for interactions and to compute the gravitational potential. The new algorithms we introduce along with our choice of decomposition scheme minimize communication costs and ensure optimal distribution of data and workload among the processing units. The implementation uses the Message Passing Interface (MPI) library for communication, which makes it portable to many different supercomputing architectures. We validate the code by calculating the evolution of clusters with initial Plummer distribution functions up to core collapse with the number of stars, N, spanning three orders of magnitude, from 10^5 to 10^7. We find that our results are in good agreement with self-similar core-collapse solutions, and the core collapse times generally agree with expectations from the literature. Also, we observe good total energy conservation, within less than 1% throughout all simulations. We analyze the performance of the code, and demonstrate near-linear scaling of the runtime with the number of processors up to 64 processors for N=10^5, 128 for N=10^6 and 256 for N=10^7. The runtime reaches a saturation with the addition of more processors beyond these limits which is a characteristic of the parallel sorting algorithm. The resulting maximum speedups we achieve are approximately 60x, 100x, and 220x, respectively.
We report on the properties of strong pulses from PSR B0656+14 by analyzing the data obtained using Urumqi 25-m radio telescope at 1540 MHz from August 2007 to September 2010. In 44 hrs of observational data, a total of 67 pulses with signal-to-noise ratios above a 5-{\sigma} threshold were detected. The peak flux densities of these pulses are 58 to 194 times that of the average profile, and the pulse energies of them are 3 to 68 times that of the average pulse. These pulses are clustered around phases about 5 degrees ahead of the peak of the average profile. Comparing with the width of the average profile, they are relatively narrow, with the full widths at half-maximum range from 0.28 to 1.78 degrees. The distribution of pulse-energies of the pulses follows a lognormal distribution. These sporadic strong pulses detected from PSR B0656+14 are different in character from the typical giant pulses, and from its regular pulses.
We model the evolution of a Jupiter-mass protoplanet formed by the disk instability mechanism at various radial distances accounting for the presence of the disk. Using three different disk models, it is found that a newly-formed Jupiter-mass protoplanet at radial distance of $\lesssim$ 5-10 AU cannot undergo a dynamical collapse and evolve further to become a gravitational bound planet. We therefore conclude that {\it giant planets, if formed by the gravitational instability mechanism, must form and remain at large radial distances during the first $\sim$ 10$^5-10^6$ years of their evolution}. The minimum radial distances in which protoplanets of 1 Saturn-mass, 3 and 5 Jupiter-mass protoplanets can evolve using a disk model with $\dot{M}=10^{-6} M_{Sun}/yr$ and $\alpha=10^{-2}$ are found to be 12, 9, and 7 AU, respectively. The effect of gas accretion on the planetary evolution of a Jupiter-mass protoplanet is also investigated. It is shown that gas accretion can shorten the pre-collapse timescale substantially. Our study suggests that the timescale of the pre-collapse stage does not only depend on the planetary mass, but is greatly affected by the presence of the disk and efficient gas accretion.
Late-type stars interact with their close-in planets through their coronal magnetic fields. We introduce a theory for the interaction between the stellar and planetary fields focussing on the processes that release magnetic energy in the stellar coronae. We consider the energy dissipated by the reconnection between the stellar and planetary magnetic fields as well as that made available by the modulation of the magnetic helicity of the coronal field produced by the orbital motion of the planet. We estimate the powers released by both processes in the case of axisymmetric and non-axisymmetric, linear and non-linear force-free coronal fields finding that they scale as v_r (B_s)^(4/3) (B_p)^(2/3) (R_p)^2, where v_r is the relative velocity between the stellar and planetary fields, B_s the mean stellar surface field, B_p the planetary field at the poles, and R_p the radius of the planet. A chromospheric hot spot or a flaring activity phased to the orbital motion of the planet are found only when the stellar field is axisymmetric. In the case of a non-axisymmetric field, the time modulation of the energy release is multiperiodic and can be easily confused with the intrinsic stellar variability. We apply our theory to the systems with some reported evidence of star-planet magnetic interaction finding a dissipated power at least one order of magnitude smaller than that emitted by the chromospheric hot spots. The phase lags between the planets and the hot spots are reproduced by our models in all the cases except for upsilon And. In conclusion, the chromospheric hot spots rotating in phase with the planets cannot be explained by the energy dissipation produced by the interaction between stellar and planetary fields as considered by our models and require a different mechanism.
We present observational data for two main components (S255IR and S255N) of the S255 high mass star forming region in continuum and molecular lines obtained at 1.3 mm and 1.1 mm with the SMA, at 1.3 cm with the VLA and at 23 and 50 cm with the GMRT. The angular resolution was from ~ 2" to ~ 5" for all instruments. With the SMA we detected a total of about 50 spectral lines of 20 different molecules (including isotopologues). About half of the lines and half of the species (in particular N2H+, SiO, C34S, DCN, DNC, DCO+, HC3N, H2CO, H2CS, SO2) have not been previously reported in S255IR and partly in S255N at high angular resolution. Our data reveal several new clumps in the S255IR and S255N areas by their millimeter wave continuum emission. Masses of these clumps are estimated at a few solar masses. The line widths greatly exceed expected thermal widths. These clumps have practically no association with NIR or radio continuum sources, implying a very early stage of evolution. At the same time, our SiO data indicate the presence of high-velocity outflows related to some of these clumps. In some cases, strong molecular emission at velocities of the quiescent gas has no detectable counterpart in the continuum. We discuss the main features of the distribution of NH3, N2H+, and deuterated molecules. We estimate properties of decimeter wave radio continuum sources and their relationship with the molecular material.
A radiation-magnetohydrodynamic simulation for the black hole-torus system is performed in the framework of full general relativity for the first time. A truncated moment formalism is employed for a general relativistic neutrino radiation transport. Several systems in which the black hole mass is $M_{\rm BH}=3$ or $6M_{\odot}$, the black hole spin is zero, and the torus mass is $\approx 0.14$--$0.38M_{\odot}$ are evolved as models of the remnant formed after the merger of binary neutron stars or black hole-neutron star binaries. The equation of state and microphysics for the high-density and high-temperature matter are phenomenologically taken into account in a semi-quantitative manner. It is found that the temperature in the inner region of the torus reaches $\agt 10$ MeV which enhances a high luminosity of neutrinos $\sim 10^{51}$ ergs/s for $M_{\rm BH}=6M_{\odot}$ and $\sim 10^{52}$ ergs/s for $M_{\rm BH}=3M_{\odot}$. It is shown that neutrinos are likely to be emitted primarily toward the outward direction in the vicinity of the rotational axis and their energy density may be high enough to launch a low-energy short gamma-ray burst via the neutrino-antineutrino pair-annihilation process with the total energy deposition $\sim 10^{47}$--$10^{49}$ ergs. It is also shown in our model that for $M_{\rm BH}=3M_{\odot}$, the neutrino luminosity is larger than the electromagnetic luminosity while for $M_{\rm BH}=6M_{\odot}$, the neutrino luminosity is comparable to or slightly smaller than the electromagnetic luminosity.
We statistically study the property of emerging flux regions (EFRs) and the upper solar atmosphere response to the flux emergence by using data from the Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Parameters including the total emerged flux, the flux growth rate, the maximum area, the duration of the emergence and the separation speed of the opposite polarities are adopted to delineate the property of the EFRs. The response of the upper atmosphere is addressed by the response of the atmosphere at different wavelengths (and thus at different temperatures). According to our results, the total emerged fluxes are in the range of (0.44 -- 11.2)$\times10^{19}$ Mx while the maximum area ranges from 17 to 182 arcsec$^2$. The durations of the emergence are between 1 and 12 hours, which are positively correlated to both the total emerged flux and the maximum area. The maximum distances between the opposite polarities are 7 -- 25 arcsec and are also correlated to the duration positively. The separation speeds are from 0.05 to 1.08 km s$^{-1}$, negatively correlated to the duration. The derived flux growth rates are (0.1 -- 1.3)$\times10^{19}$ Mx hr$^{-1}$, which are positively correlated to the total emerging flux. The upper atmosphere responds to the flux emergence in the 1600\AA\ chromospheric line first, and then tens and hundreds of seconds later, in coronal lines, such as the 171\AA\ (T=10$^{5.8}$ K) and 211\AA\ (T=10$^{6.3}$ K) lines almost simultaneously, suggesting the successively heating of atmosphere from the chromosphere to the corona.
We describe the current status of our numerical simulations for the collapse of a massive stellar core to a BH and the BNS mergers, performed in the framework of full general relativity incorporating finite-temperature EOS and neutrino cooling. For the stellar core collapse simulation, we present the latest numerical results. We employed a purely nucleonic EOS (Shen-EOS). As an initial condition, we adopted a 100 $M_{\odot}$ presupernova model calculated by Umeda and Nomoto. Changing the degree of rotation for the initial condition, we clarify the strong dependence of the outcome of the collapse on this. When the rotation is rapid enough, the shock wave formed at the core bounce is deformed to be a torus-like shape. Then, the infalling matter is accumulated in the central region due to the oblique shock at the torus surface, hitting the PNS and dissipating the kinetic energy there. As a result, outflows can be launched. The PNS eventually collapses to a BH and an accretion torus is formed around it. We also found that the evolution of the BH and torus depends strongly on the rotation initially given. In the BNS merger simulations, we in addition employ an EOS incorporating a degree of freedom for hyperons. The numerical simulations show that for the purely nucleonic EOS, a HMNS with a long lifetime ($\gg 10$ ms) is the outcome for the total mass $M \lesssim 3.0M_{\odot}$. By contrast, the formed HMNS collapses to a BH in a shorter time scale with the hyperonic EOS for $M \gtrsim 2.7M_{\odot}$. It is shown that the typical total neutrino luminosity of the HMNS is $\sim 3$--$10\times 10^{53}$ ergs/s and the effective amplitude of gravitational waves from the HMNS is 2--$6 \times 10^{-22}$ at $f\approx 2$--2.5 kHz for a source distance of 100 Mpc.
The H II regions LMC N191 and SMC N77 are among the outermost massive star-forming regions in the Magellanic Clouds. So far, few works have dealt with these objects despite their interesting characteristics. We aim at studying various physical properties of these objects regarding their morphology (in the optical and Spitzer IRAC wavelengths), ionized gas emission, nebular chemical abundances, exciting sources, stellar content, age, presence or absence of young stellar objects, etc. This study is based mainly on optical ESO NTT observations, both imaging and spectroscopy, coupled with other archive data, notably Spitzer images (IRAC 3.6, 4.5, 5.8, and 8.0 microns) and 2MASS observations. We show the presence of two compact H II regions, a low-excitation blob (LEB) named LMC N191A and a high-excitation blob (HEB) named SMC N77A, and study their properties and those of their exciting massive stars as far as spectral type and mass are concerned. We also analyze the environmental stellar populations and determine their evolutionary stages. Based on Spitzer IRAC data, we characterize the YSO candidates detected in the direction of these regions. Massive star formation is going on in these young regions with protostars of mass about 10 and 20 M_sun in the process of formation.
Far-ultraviolet (FUV) and far-infrared (FIR) luminosity functions (LFs) of galaxies show a strong evolution from $z = 0$ to $z = 1$, but the FIR LF evolves much stronger than the FUV one. The FUV is dominantly radiated from newly formed short-lived OB stars, while the FIR is emitted by dust grains heated by the FUV radiation field. It is known that dust is always associated with star formation activity. Thus, both FUV and FIR are tightly related to the star formation in galaxies, but in a very complicated manner. In order to disentangle the relation between FUV and FIR emissions, we estimate the UV-IR bivariate LF (BLF) of galaxies with {\sl GALEX} and {\sl AKARI} All-Sky Survey datasets. Recently we invented a new mathematical method to construct the BLF with given marginals and prescribed correlation coefficient. This method makes use of a tool from mathematical statistics, so called "copula". The copula enables us to construct a bivariate distribution function from given marginal distributions with prescribed correlation and/or dependence structure. With this new formulation and FUV and FIR univariate LFs, we analyze various FUV and FIR data with {\sl GALEX}, {\sl Spitzer}, and {\sl AKARI} to estimate the UV-IR BLF. The obtained BLFs naturally explain the nonlinear complicated relation between FUV and FIR emission from star-forming galaxies. Though the faint-end of the BLF was not well constrained for high-$z$ samples, the estimated linear correlation coefficient $\rho$ was found to be very high, and is remarkably stable with redshifts (from 0.95 at $z = 0$ to 0.85 at $z = 1.0$). This implies the evolution of the UV-IR BLF is mainly due to the different evolution of the univariate LFs, and may not be controlled by the dependence structure.
The extremely efficient process of resonant Compton upscattering by relativistic electrons in high magnetic fields is believed to be a leading emission mechanism of high field pulsars and magnetars in the production of intense X-ray radiation. New analytic developments for the Compton scattering cross section using Sokolov & Ternov (S&T) states with spin-dependent resonant widths are presented. These new results display significant numerical departures from both the traditional cross section using spin-averaged widths, and also from the spin-dependent cross section that employs the Johnson & Lippmann (J&L) basis states, thereby motivating the astrophysical deployment of this updated resonant Compton formulation. Useful approximate analytic forms for the cross section in the cyclotron resonance are developed for S&T basis states. These calculations are applied to an inner magnetospheric model of the hard X-ray spectral tails in magnetars, recently detected by RXTE and INTEGRAL. Relativistic electrons cool rapidly near the stellar surface in the presence of intense baths of thermal X-ray photons. We present resonant Compton cooling rates for electrons, and the resulting photon spectra at various magnetospheric locales, for magnetic fields above the quantum critical value. These demonstrate how this scattering mechanism has the potential to produce the characteristically flat spectral tails observed in magnetars.
We present preliminary results of a pulsar population synthesis of normal pulsars from the Galactic disk using a Markov Chain Monte Carlo method to better understand the parameter space of the assumed model. We use the Kuiper test, similar to the Kolmogorov-Smirnov test, to compare the cumulative distributions of chosen observables of detected radio pulsars with those simulated for various parameters. Our code simulates pulsars at birth using Monte Carlo techniques and evolves them to the present assuming initial spatial, kick velocity, magnetic field, and period distributions. Pulsars are spun down to the present, given radio and gamma-ray emission characteristics, filtered through ten selected radio surveys, and a {\it Fermi} all-sky threshold map. Each chain begins with a different random seed and searches a ten-dimensional parameter space for regions of high probability for a total of one thousand different simulations before ending. The code investigates both the "large world" as well as the "small world" of the parameter space. We apply the K-means clustering algorithm to verify if the chains reveal a single or multiple regions of significance. The outcome of the combined set of chains is the weighted average and deviation of each of the ten parameters describing the model. While the model reproduces reasonably well the detected distributions of normal radio pulsars, it does not replicate the predicted detected $\dot P - P$ distribution of {\it Fermi} pulsars. The simulations do not produce sufficient numbers of young, high-$\dot E$ pulsars in the Galactic plane.
The characteristic formulation of the relativistic hydrodynamic equations (Donat et al 1998 J. Comput. Phys. 146 58), which has been implemented in many relativistic hydro-codes that make use of Godunov-type methods, has to be slightly modified in the case of evolving barotropic flows. For a barotropic equation of state, a removable singularity appears in one of the eigenvectors. The singularity can be avoided by means of a simple renormalization which makes the system of eigenvectors well defined and complete. An alternative strategy for the particular case of barotropic flows is discussed.
CW Leo has been observed six times between October 2009 and June 2012 with the SPIRE instrument on board the Herschel satellite. Variability has been detected in the flux emitted by the central star with a period of 639 \pm 4 days, in good agreement with determinations in the literature. Variability is also detected in the bow shock around CW Leo that had previously been detected in the ultraviolet and Herschel PACS/SPIRE data. Although difficult to prove directly, our working hypothesis is that this variability is directly related to that of the central star. In this case, fitting a sine curve with the period fixed to 639 days results in a time-lag in the variability between bow shock and the central star of 402 \pm 37 days. The orientation of the bow shock relative to the plane of the sky is unknown (but see below). For an inclination angle of zero degrees, the observed time-lag translates into a distance to CW Leo of 130 \pm 13 pc, and for non-zero inclination angles the distance is smaller. Fitting the shape of the bow shock with an analytical model (Wilkin 1996), the effect of the inclination angle on the distance may be estimated. Making the additional assumption that the relative peculiar velocity between the interstellar medium (ISM) and CW Leo is determined entirely by the star space velocity with respect to the local standard of rest (i.e. a stationary ISM), the inclination angle is found to be (-33.3 \pm 0.8) degrees based on the observed proper motion and radial velocity. Using the Wilkin model, our current best estimate of the distance to CW Leo is 123 \pm 14 pc. For a distance of 123 pc, we derive a mean luminosity of 7790 \pm 150 Lsol (internal error).
We present a spectroscopic catalog of the 1,556 brightest M dwarf candidates in the northern sky, as selected by proper motion and photometry. These bright sources comprise >99% of the known, northern M dwarfs with apparent magnitudes J<9, and most likely include >95% of all such existing objects. Only 679 stars in our sample are listed in the Third Catalog of Nearby Stars (CNS3); most others are relative unknowns and have spectroscopic data presented here for the first time. Observations confirm 1,403 of the candidates to be late-K and M dwarfs with spectral subtypes K7-M6, with subtypes assigned based on spectral index measurements of CaH and TiO molecular bands. We also calculate the Zeta parameter, which measures the ratio of TiO and CaH bandheads, and is correlated with metallicity in M dwarfs/subdwarfs, and for this we present a revised calibration based on corrected values of the CaH and TiO spectral indices. Fits of our spectra to the Phoenix atmospheric model grid are used to estimate effective temperatures. Existing geometric parallax measurements for 624 of the catalog stars are used to recalibrate the subtype/absolute magnitude relationship in M dwarfs; we find that spectroscopic distances are marginally more accurate at earlier (K7-M2) subtypes, but that photometric distances should be preferred for later-type dwarfs (M3-M6). We identify active stars from H$\alpha$ equivalent widths, GALEX UV magnitudes, and ROSAT X-ray fluxes from ROSAT. We combine proper motion data and photometric distances to evaluate the distribution in (U,V,W) velocity space of the entire catalog. The overall velocity-space distribution correlates tightly with the velocity distribution of G dwarfs in the Solar Neighborhood. However, active stars show a smaller dispersion in their space velocities, which is consistent with those stars being younger on average.
The underlying physics that generates the excitations in the global low-frequency, < 5.3 mHz, solar acoustic power spectrum is a well known process that is attributed to solar convection; However, a definitive explanation as to what causes excitations in the high-frequency regime, > 5.3 mHz, has yet to be found. Karoff and Kjeldsen (Astrophys. J. 678, 73-76, 2008) concluded that there is a correlation between solar flares and the global high-frequency solar acoustic waves. We have used the Global Oscillations Network Group (GONG) helioseismic data in an attempt to verify Karoff and Kjeldsen (2008) results as well as compare the post-flare acoustic power spectrum to the pre-flare acoustic power spectrum for 31 solar flares. Among the 31 flares analyzed, we observe that a decrease in acoustic power after the solar flare is just as likely as an increase. Furthermore, while we do observe variations in acoustic power that are most likely associated with the usual p-modes associated with solar convection, these variations do not show any significant temporal association with flares. We find no evidence that consistently supports flare driven high-frequency waves.
The rotational spectrum of the higher-energy trans conformational isomer of methyl formate has been assigned for the first time using several pulsed-jet Fourier transform microwave spectrometers in the 6-60 GHz frequency range. This species has also been sought toward the Sagittarius B2(N) molecular cloud using the publicly available PRIMOS survey from the Green Bank Telescope. We detect seven absorption features in the survey that coincide with laboratory transitions of trans-methyl formate, from which we derive a column density of 3.1 (+2.6, -1.2) \times 10^13 cm-2 and a rotational temperature of 7.6 \pm 1.5 K. This excitation temperature is significantly lower than that of the more stable cis conformer in the same source but is consistent with that of other complex molecular species recently detected in Sgr B2(N). The difference in the rotational temperatures of the two conformers suggests that they have different spatial distributions in this source. As the abundance of trans-methyl formate is far higher than would be expected if the cis and trans conformers are in thermodynamic equilibrium, processes that could preferentially form trans-methyl formate in this region are discussed. We also discuss measurements that could be performed to make this detection more certain. This manuscript demonstrates how publicly available broadband radio astronomical surveys of chemically rich molecular clouds can be used in conjunction with laboratory rotational spectroscopy to search for new molecules in the interstellar medium.
Models of inhomogeneous universes constructed with exact solutions of Einstein's General Relativity have been proposed in the literature with the aim of reproducing the cosmological data without any need for a dark energy component. Besides large scale inhomogeneity models spherically symmetric around the observer, Swiss-cheese models have also been studied. Among them, Swiss-cheeses where the inhomogeneous patches are modeled by different particular Szekeres solutions have been used for reproducing the apparent dimming of the type Ia supernovae (SNIa). However, the problem of fitting such models to the SNIa data is completely degenerate and we need other constraints to fully characterize them. One of the tests which is known to be able to discriminate between different cosmological models is the redshift drift. This drift has already been calculated by different authors for Lema\^itre-Tolman-Bondi (LTB) models. We compute it here for one particular axially symmetric quasi-spherical Szekeres (QSS) Swiss-cheese which has previously been shown to reproduce to a good accuracy the SNIa data, and we compare the results to the drift in the LCDM model and in some LTB models that can be found in the literature. We show that it is a good discriminator between them. Then, we discuss our model's remaining degrees of freedom and propose a recipe to fully constrain them.
We argue that one of the basic assumptions of the Bondi accretion process, that the accreting object has zero pressure, might not hold in many galaxies because of the pressure exerted by stellar winds of star orbiting the central super massive black hole (SMBH). Hence, the Bondi accretion cannot be used in these cases, such as in the galaxy NGC 3115. The winds of these high-velocity stars are shocked to temperatures above the virial temperature of the galaxy, leading to the formation of a hot bubble of size ~0.1-10 pc near the center. This hot bubble can substantially reduce the mass accretion rate by the SMBH. If the density of the hot bubble is lower than that of the interstellar medium (ISM), a density-inversion layer is formed. Adding to other problems of the Bondi process, our results render the Bondi accretion irrelevant for AGN feedback in cooling flow in galaxies and small groups of galaxies and during galaxy formation.
We present numerical simulations of the adiabatic interaction of a shock with a clumpy region containing many individual clouds. Our work incorporates a sub-grid turbulence model which for the first time makes this investigation feasible. We vary the Mach number of the shock, the density contrast of the clouds, and the ratio of total cloud mass to inter-cloud mass within the clumpy region. Cloud material becomes incorporated into the flow. This "mass-loading" reduces the Mach number of the shock, and leads to the formation of a dense shell. In cases in which the mass-loading is sufficient the flow slows enough that the shock degenerates into a wave. The interaction evolves through up to four stages: initially the shock decelerates; then its speed is nearly constant; next the shock accelerates as it leaves the clumpy region; finally it moves at a constant speed close to its initial speed. Turbulence is generated in the post-shock flow as the shock sweeps through the clumpy region. Clouds exposed to turbulence can be destroyed more rapidly than a similar cloud in an "isolated" environment. The lifetime of a downstream cloud decreases with increasing cloud-to-intercloud mass ratio. We briefly discuss the significance of these results for starburst superwinds and galaxy evolution.
We present follow-up observations and analysis of the recently discovered short period low-mass eclipsing binary, SDSS J001641-000925. With an orbital period of 0.19856 days, this system belongs to a very rare class of contact eclipsing binaries, and has one of the shortest known periods for an M dwarf binary system. Medium-resolution spectroscopy and multi-band photometry for the system are presented. Markov chain Monte Carlo modeling of the light curves and radial velocities yield estimated masses for the stars of M_1 =0.54+/-0.07M_sun and M_2 =0.34+/-0.04M_sun, and radii of R_1 =0.68+/-0.03 R_sun and R_2 = 0.58 +/- 0.03 R_sun respectively. An overcontact scenario is strongly preferred by the binary model. Both stellar components are found to exhibit magnetic activity through H_alpha emission. Using both sparsely sampled survey photometry and dedicated monitoring, the orbital period is found to decrease by dP/dt ~ 8 s yr^{-1}. This is one of the largest amplitude period decays observed for a W UMa type binary, indicating that the system is in contact and losing angular momentum. SDSS J001641-000925 is thus the first verified contact M dwarf binary system.
We report the first Chandra detection of emission out to the virial radius in the cluster Abell 1835 at z=0.253. Our analysis of the soft X-ray surface brightness shows that emission is present out to a radial distance of 10 arcmin or 2.4 Mpc, and the temperature profile has a factor of ten drop from the peak temperature of 10 keV to the value at the virial radius. We model the Chandra data from the core to the virial radius and show that the steep temperature profile is not compatible with hydrostatic equilibrium of the hot gas, and that the gas is convectively unstable at the outskirts. A possible interpretation of the Chandra data is the presence of a second phase of warm-hot gas near the cluster's virial radius that is not in hydrostatic equilibrium with the cluster's potential.
We model the dynamics of continuum driven winds, and show that the skirt and twin lobe structure are a generic property of critically rotating super-Eddington stars. Moreover, we show that if \eta-Carinae began its life with a high enough angular momentum, the present day wind is sufficiently concentrated towards the poles to have driven the star towards critical rotation.
We use the photometric redshift method of Chakrabarti & McKee (2008) to infer photometric redshifts of submillimeter galaxies with far-IR (FIR) $\it{Herschel}$ data obtained as part of the PACS Evolutionary Probe (PEP) program. For the sample with spectroscopic redshifts, we demonstrate the validity of this method over a large range of redshifts ($ 4 \ga z \ga 0.3$) and luminosities, finding an average accuracy in $(1+z_{\rm phot})/(1+z_{\rm spec})$ of 10%. Thus, this method is more accurate than other FIR photometric redshift methods. This method is different from typical FIR photometric methods in deriving redshifts from the light-to-gas mass ($L/M$) ratio of infrared-bright galaxies inferred from the FIR spectral energy distribution (SED), rather than dust temperatures. Once the redshift is derived, we can determine physical properties of infrared bright galaxies, including the temperature variation within the dust envelope, luminosity, mass, and surface density. We use data from the GOODS-S field to calculate the star formation rate density (SFRD) of sub-mm bright sources detected by AzTEC and PACS. The AzTEC-PACS sources, which have a threshold $850 \micron$ flux $\ga 5 \rm mJy$, contribute 15% of the SFRD from all ULIRGs ($L_{\rm IR} \ga 10^{12} L_{\odot}$), and 3% of the total SFRD at $z \sim 2$.
New multi-color UBVR light curves of the eclipsing binary KR Cyg were obtained in 2005. Photometric solutions were derived using the Wilson- Devinney method. The result shows that KR Cyg is a near-contact binary system with a large effective temperature difference between the components, approximately 5230 K. All the times of minimum light were collected and combined with our observations obtained in 2010 and 2011. Analysing all the times of mid-eclipse, we found for the first time a possible periodic oscillation with an amplitude of 0.001 days and a period of ~76 years. The periodic oscillation could be explained by the light-time effect due to a presumed third component.
Determining the heating mechanism (or mechanisms) that causes the outer atmosphere of the Sun, and many other stars, to reach temperatures orders of magnitude higher than their surface temperatures has long been a key problem. For decades the problem has been known as the coronal heating problem, but it is now clear that `coronal heating' cannot be treated or explained in isolation and that the heating of the whole solar atmosphere must be studied as a highly coupled system. The magnetic field of the star is known to play a key role, but, despite significant advancements in solar telescopes, computing power and much greater understanding of theoretical mechanisms, the question of which mechanism or mechanisms are the dominant supplier of energy to the chromosphere and corona is still open. Following substantial recent progress, we consider the most likely contenders and discuss the key factors that have made, and still make, determining the actual (coronal) heating mechanism (or mechanisms) so difficult.
In this paper we study the kinetic theory of many-particle astrophysical systems imposing axial symmetry and extending our previous analysis in Phys. Rev. D 83, 123007 (2011). Starting from a Newtonian model describing a collisionless self-gravitating gas, we develop a framework to include systematically the first general relativistic corrections to the matter distribution and gravitational potentials for general stationary systems. Then, we use our method to obtain particular solutions for the case of the Morgan & Morgan disks. The models obtained are fully analytical and correspond to the post-Newtonian generalizations of classical ones. We explore some properties of the models in order to estimate the importance of post-Newtonian corrections and we find that, contrary to the expectations, the main modifications appear far from the galaxy cores. As a by-product of this investigation we derive the corrected version of the tensor virial theorem. For stationary systems we recover the same result as in the Newtonian theory. However, for time dependent backgrounds we find that there is an extra piece that contributes to the variation of the inertia tensor.
We consider a generalization of the Randall-Sundrum single brane-world scenario (RS2). More precisely, the generalization is described through curvature corrections, corresponding to a Gauss-Bonnet term in the bulk and a Hilbert-Einstein term, as well as the strength of the induced gravity term, on the brane. We are mainly interested in analyzing the early inflationary era of the brane, which we model within the extreme slow-roll limit, i.e., under a de Sitter like brane inflation, where the inflaton field is confined on the brane. We compute the scalar perturbations in this model and compare our results with those previously obtained for the RS2 scenario with and without an induced gravity term on the brane or a Gauss-Bonnet term in the bulk. The amplitude of the scalar perturbations is decreased as compared with a pure RS2 model. In addition, the effect from the Gauss-Bonnet correction in an induced gravity brane-world model is to decrease the amplitude of the scalar perturbations, and a similar result is obtained for the induced gravity effect in a Gauss-Bonnet brane-world. In general, in the high energy limit the amplitude is highly suppressed by the Gauss-Bonnet effect. Finally, we constrain the model using the latest WMAP7 data.
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We present results from spherically symmetric (1D) and axially symmetric (2D) core-collapse supernova simulations. Our model is based on neutrino radiation hydrodynamics, including spectral neutrino transport. We apply the equations of state (EOS) from Lattimer & Swesty (LS) and Shen et al. (SHEN), and explore the differences obtained during the post-bounce phase prior to the possible onset of a neutrino-driven explosion. We confirm that in 1D simulations neutrino-driven explosions cannot be obtained for any of the employed EOS. In 2D, EOS induced structural differences lead to a more efficient neutrino heating, in particular for LS in comparison to the simulations that use SHEN. For simulations of the 15 M_sun progenitor with LS under investigation, it results in a continuous expansion of the stalled bounce shock to increasingly larger radii, which is absent using SHEN. Simulations of a 11.2 M_sun progenitor result in neutrino-driven explosions for all EOS under investigation, however slightly more powerful for LS than for SHEN and also slightly delayed for the latter. The generally more efficient neutrino heating using LS can be related to the higher electron antineutrino luminosity and the more mass enclosed inside the gain region. It also leads to the development of an aspherical downflow of material from large radii to the central protoneutron star surface for LS, which in turn supplies continuously energy to the protoneutron star. Moreover, we investigate several additional indicators of the explosion, e.g., the amplitude of the standing-accretion shock instability mode, the mass weighted average entropy in the gain region, the protoneutron star radius, the antesonic condition, and the ratio of advection and heating timescales.
We have performed 323 MHz observations with the Giant Metrewave Radio Telescope of the most promising candidates selected from the MACS catalog. The aim of the work is to extend our knowledge of the radio halo and relic populations to z>0.3, the epoch in which massive clusters formed. In MACSJ1149.5+2223 and MACSJ1752.1+4440, we discovered two double-relic systems with a radio halo, and in MACSJ0553.4-3342 we found a radio halo. Archival Very Large Array observations and Westerbork Synthesis Radio Telescope observations have been used to study the polarization and spectral index properties. The radio halo in MACSJ1149.5+2223 has the steepest spectrum ever found so far in these objects (alpha > 2). The double relics in MACSJ1149.5+2223 are peculiar in their position that is misaligned with the main merger axis. The relics are polarized up to 30% and 40% in MACSJ1149.5+2223 and MACSJ1752.040+44, respectively. In both cases, the magnetic field is roughly aligned with the relics' main axes. The spectra in the relics in MACSJ1752.040+44 steepen towards the cluster centre, in agreement with model expectations. X-ray data on MACSJ0553.4-3342 suggests that this cluster is undergoing a major merger, with the merger axis close to the plane of the sky. The cores of the disrupted clusters have just passed each other, but no radio relic is detected in this system. If turbulence is responsible for the radio emission, we argue that it must develop before the core passage. A comparison of double relic plus halo system with cosmological simulations allows a simultaneous estimate of the acceleration efficiencies at shocks (to produce relics) and of turbulence (to produce the halo).
A first characterization of many exoplanets has recently been achieved by the observational determination of their radius. For some planets, a measurement of the luminosity has also been possible, with many more directly imaged planets expected in the future. The statistical characterization of exoplanets through their mass-radius and mass-luminosity diagram is thus becoming possible. This is for planet formation and evolution theory of similar importance as the mass-distance diagram. Our aim in this and a companion paper is to extend our formation model into a coupled formation and evolution model. We want to calculate in a self-consistent way all basic characteristics (M,a,R,L) of a planet and use the model for population synthesis calculations. Here we show how we solve the structure equations describing the gaseous envelope not only during the early formation phase, but also during gas runaway accretion, and during the evolutionary phase at constant mass on Gyr timescales. We then study the in situ formation and evolution of Jupiter, the mass-radius relationship of giants, the influence of the core mass on the radius and the luminosity both in the "hot start" and the "cold start" scenario. We put special emphasis on the comparison with other models. We find that our results agree very well with those of more complex models, despite a number of simplifications. The upgraded model yields the most important characteristics of a planet from its beginning as a seed embryo to a Gyr old planet. This is the case for all planets in a synthetic planetary population. Therefore, we can now use self-consistently the statistical constraints coming from all major observational techniques. This is important in a time where different techniques yield constraints on very diverse sub-populations of planets, and where its is challenging to put all these constraints together in one coherent picture.
Context: The ESO Public Survey "VISTA Variables in the V\'ia L\'actea" (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. Aims: The VVV observations will foster the construction of a sample of Galactic star clusters with reliable and homogeneously derived physical parameters (e.g., age, distance, and mass, etc.). In this first paper in a series, the methodology employed to establish cluster parameters for the envisioned database are elaborated upon by analyzing a subsample of 4 known young open clusters: Danks 1, Danks 2, RCW 79, and DBS 132. The analysis offers a first glimpse of the information that can be gleaned for the final cluster database from the VVV observations. Methods: Wide-field, deep JHKs VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters for a subset of clusters. Results: Results inferred from the deep near-infrared photometry which features mitigated uncertainties (e.g. the accuracy of the photometry is better than 0.1mag for Ks<18mag), the wide field-of-view of the VVV survey, and numerous high quality low resolution spectra (typically more than 10 per cluster), are used to establish independent cluster parameters which enable existing determinations to be assessed. An anomalous reddening law in the direction toward the Danks' clusters is found, i.e. E(J-H)/E(H-Ks)=2.20+/-0.06, which exceeds published values for the inner Galaxy. The G305 star forming complex, which includes the Danks' clusters, lies beyond the Sagittarius-Carina spiral arm and occupies the Centaurus arm. Finally, the first deep infrared color-magnitude diagram of RCW 79 is presented which reveal a sizable pre-main sequence population. A list of candidate variable stars in G305 region is reported.
We provide evidence that the obliquities of stars with close-in giant planets were initially nearly random, and that the low obliquities that are often observed are a consequence of star-planet tidal interactions. The evidence is based on 14 new measurements of the Rossiter-McLaughlin effect (for the systems HAT-P-6, HAT-P-7, HAT-P-16, HAT-P-24, HAT-P-32, HAT-P-34, WASP-12, WASP-16, WASP-18, WASP-19, WASP-26, WASP-31, Gl 436, and Kepler-8), as well as a critical review of previous observations. The low-obliquity (well-aligned) systems are those for which the expected tidal timescale is short, and likewise the high-obliquity (misaligned and retrograde) systems are those for which the expected timescale is long. At face value, this finding indicates that the origin of hot Jupiters involves dynamical interactions like planet-planet interactions or the Kozai effect that tilt their orbits, rather than inspiraling due to interaction with a protoplanetary disk. We discuss the status of this hypothesis and the observations that are needed for a more definitive conclusion.
Dust extinction and reddening are ubiquitous in astronomical observations and are often a major source of systematic uncertainty. We present here a study of the correlation between extinction in the Milky Way and the equivalent width of the NaI D absorption doublet. Our sample includes more than 100 high resolution spectra from the KECK telescopes and nearly a million low resolution spectra from the Sloan Digital Sky Survey (SDSS). We measure the correlation to unprecedented precision, constrain its shape, and derive an empirical relation between these quantities with a dispersion of order 0.15 magnitude in E(B-V). From the shape of the curve of growth we further show that a typical sight line through the Galaxy crosses about three dust clouds. We provide a brief guide on how to best estimate extinction to extragalactic sources such as supernovae, using the NaI D absorption feature, under a variety of circumstances.
We present structural measurements of galaxies in the z~0.06 groups of the Zurich Environmental Study (ZENS), a program aimed at establishing how galaxy properties depend on four different environmental parameters. Galaxy structure is quantified both non-parametrically and parametrically, through modeling of the two-dimensional surface brightness profiles of the galaxies. Structural parameters are also derived for subgalactic components, i.e., bulges, disks and bars. We calibrate all structural measurements on a common grid, correcting for biases due to PSF and surface brightness effects as a function of galaxy size, magnitude, light concentration and ellipticity. We use the galaxy bulge-to-total ratios (B/T), in combination with the calibrated non-parametric structural estimators, to implement a quantitative morphological classification scheme that maximizes purity in the morphological classes. We focus on how the concentration (C) of satellite galaxies depends on galaxy mass for separate Hubble types, and on halo mass, group-centric distance and large-scale structure density. At galaxy masses M>10^10 Msun, the concentration of disk satellites is found to increase, with increasing stellar mass, separately within each morphological bin, implying that the increase in C with increasing stellar mass for disk satellites is due, at least in part, to an increase in the galaxy central stellar density at constant B/T. The correlation between C and stellar mass becomes progressively steeper for later morphological types. Disk-satellite concentration shows no dependence on either large-scale structure density or projected group-centric distance. In contrast, at constant galaxy stellar mass above 10^10 Msun the mass of the group halo appears to have an impact on the concentration of disk-dominated satellites being 10% more concentrated in M>10^13.4 Msun groups than in lower mass groups. [Abridged]
The giant planet orbiting tau Bootis was among the first extrasolar planets to be discovered through the reflex motion of its host star. It is one of the brightest known and most nearby planets with an orbital period of just a few days. Over the course of more than a decade, measurements of its orbital inclination have been announced and refuted, and have subsequently remained elusive until now. Here we report on the detection of carbon monoxide absorption in the thermal day-side spectrum of tau Bootis b. At a spectral resolution of R~100,000, we trace the change in the radial velocity of the planet over a large range in phase, determining an orbital inclination of i=44.5+-1.5 degrees and a true planet mass of 5.95+-0.28 MJup. This result extends atmospheric characterisation to non-transiting planets. The strong absorption signal points to an atmosphere with a temperature that is decreasing towards higher altitudes. This is a stark contrast to the temperature inversion invoked for other highly irradiated planets, and supports models in which the absorbing compounds believed to cause such atmospheric inversions are destroyed by the ultraviolet emission from the active host star.
Observational studies have revealed a "downsizing" trend in black hole (BH) growth: the number densities of luminous AGN peak at higher redshifts than those of faint AGN. This would seem to imply that massive black holes formed before low mass black holes, in apparent contradiction to hierarchical clustering scenarios. We investigate whether this observed "downsizing" in BH growth is reproduced in a semi-analytic model for the formation and evolution of galaxies and black holes, set within the hierarchical paradigm for structure formation (Somerville et al. 2008; S08). In this model, black holes evolve from light seeds (\sim100M\odot) and their growth is merger-driven. The original S08 model (baseline model) reproduces the number density of AGN at intermediate redshifts and luminosities, but underproduces luminous AGN at very high redshift (z > 3) and overproduces them at low redshift (z < 1). In addition, the baseline model underproduces low-luminosity AGN at low redshift (z < 1). To solve these problems we consider several modifications to the physical processes in the model: (1) a 'heavy' black hole seeding scenario (2) a sub-Eddington accretion rate ceiling that depends on the cold gas fraction, and (3) an additional black hole accretion mode due to disk instabilities. With these three modifications, the models can explain the observed downsizing, successfully reproduce the bolometric AGN luminosity function and simultaneously reproduce galaxy and black hole properties in the local Universe. We also perform a comparison with the observed soft and hard X-ray luminosity functions of AGN, including an empirical correction for torus-level obscuration, and reach similar conclusions. Our best-fit model suggests a scenario in which disk instabilities are the main driver for moderately luminous Seyfert galaxies at low redshift, while major mergers are the main trigger for luminous AGN.
We analyze the spectral energy distributions (SEDs) of Lyman break galaxies (LBGs) at z=1-3 selected using the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS channel filters. These HST/WFC3 observations cover about 50 sq. arcmin in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z=1-3 are selected using dropout selection criteria similar to high redshift LBGs. The deep multi-band photometry in this field is used to identify best-fit SED models, from which we infer the following results: (1) the photometric redshift estimate of these dropout selected LBGs is accurate to within few percent; (2) the UV spectral slope {\beta} is redder than at high redshift (z>3), where LBGs are less dusty; (3) on average, LBGs at z=1-3 are massive, dustier and more highly star-forming, compared to LBGs at higher redshifts with similar luminosities, though their median values are similar within 1{\sigma} uncertainties. This could imply that identical dropout selection technique, at all redshifts, find physically similar galaxies; and (4) stellar masses of these LBGs are directly proportional to their UV luminosities with a logarithmic slope of ~0.46, and star-formation rates are proportional to their stellar masses with a logarithmic slope of ~0.90. These relations hold true --- within luminosities probed in this study --- for LBGs from z~1.5 to 5. The star-forming galaxies selected using other color-based techniques show similar correlations at z~2, but to avoid any selection biases, and for direct comparison with LBGs at z>3, a true Lyman break selection at z~2 is essential. The future HST UV surveys, both wider and deeper, covering a large luminosity range are important to better understand LBG properties, and their evolution.
We study the possibility that particle production during inflation could source observable gravity waves on scales relevant for Cosmic Microwave Background experiments. A crucial constraint on such scenarios arises because particle production can also source inflaton perturbations, and might ruin the usual predictions for a nearly scale invariant spectrum of nearly Gaussian curvature fluctuations. To minimize this effect, we consider two models of particle production in a sector that is only gravitationally coupled to the inflaton. For a single instantaneous burst of massive particle production, we find that localized features in the scalar spectrum and bispectrum might be observable, but gravitational wave signatures are unlikely to be detectable (due to the suppressed quadrupole moment of non-relativistic quanta) without invoking some additional effects. We also consider a model with a rolling pseudoscalar that leads to a continuous production of relativistic gauge field fluctuations during inflation. Here we find that gravitational waves from particle production can actually exceed the usual inflationary vacuum fluctuations in a regime where non-Gaussianity is consistent with observational limits. In this model observable B-mode polarization can be obtained for any choice of inflaton potential, and the amplitude of the signal is not necessarily correlated with the scale of inflation.
The newly discovered galaxy cluster 1RXS J0603.3+4214 hosts a 1.9 Mpc long, bright radio relic with a peculiar linear morphology. Using hydrodynamical +N-body AMR simulations of the merger between three initially hydrostatic clusters in an idealised setup, we are able to reconstruct the morphology of the radio relic. Based on our simulation, we can constrain the merger geometry, predict lensing mass measurements and X-ray observations. Comparing such models to X-ray, redshift and lensing data will validate the geometry of this complex merger which helps to constrain the parameters for shock acceleration of electrons that produces the radio relic.
In this study, new observations and some results of statistical analyses are presented. The largest flare data set of DO Cep in the literature has been obtained with 89 flares detected in 67.61 hours of U-band flare patrol. First of all, the observations demonstrated that the star is one of the most active flare stars in respect to the computed flare frequency. Secondly, using the independent samples t-test, the detected flares were classified into two subtypes, and then they were modelled. Analysing the models demonstrated that the fast and slow flares occurring on the star can be separated with a critical value of the ratio of their decay time to rise time. The critical value was computed as 3.40. According to this value, the fast flare rate is 20.22%, while the slow flare rate is 79.78%. Besides, there is a 39.282 times difference between the energies of these two types of flares. However, the flare equivalent durations versus the flare rise times increase in similar ways for both groups. In addition, all all the flares were modelled with the one-phase exponential association function. Analysing this model, the plateau value was found to be 2.810. Moreover, the half-life value was computed as 433.1s from the model. The maximum flare rise time was found to be 1164s, while the maximum flare total duration was found to be 3472s. The results of the flare timescales indicate that the geometry of the flaring loop on the surface of the star might be similar to those seen on analogues of DO Cep. Consequently, considering both the half-life value and flare timescales, the flares detected on the surface of DO Cep get maximum energy in longer times, while the geometries of the flaring loops or areas get smaller.
Traditional pulsar polarization sweep analysis starts from the point dipole rotating vector model (RVM) approximation. If augmented by a measurement of the sweep phase shift, one obtains an estimate of the emission altitude (Blaskiewicz, Cordes, & Wasserman). However, a more realistic treatment of field line sweepback and finite altitude effects shows that this estimate breaks down at modest altitude ~ 0.1R_{LC}. Such radio emission altitudes turn out to be relevant to the young energetic and millisecond pulsars that dominate the \gamma-ray population. We quantify the breakdown height as a function of viewing geometry and provide simple fitting formulae that allow observers to correct RVM-based height estimates, preserving reasonable accuracy to R ~ 0.3R_{LC}. We discuss briefly other observables that can check and improve height estimates.
We estimate here a flux-transport dynamo model's response time to changes in meridional flow speed. Time-variation in meridional flow primarily determines the shape of a cycle in this class of dynamo models. In order to simultaneously predict the shape, amplitude and timing of a solar cycle by implementing an Ensemble Kalman Filter in the framework of Data Assimilation Research Testbed (DART), it is important to know the model's sensitivity to flow variation. Guided by observations we consider a smooth increase or decrease in meridional flow speed for a specified time (a few months to a few years), after which the flow speed comes back to the steady speed, and implement that time-varying meridional flow at different phases of solar cycle. We find that the model's response time to change in flow speed peaks at four to six months if the flow change lasts for one year. The longer the changed flow lasts, the longer the model takes to respond. Magnetic diffusivity has no influence in model's response to flow variation as long as the dynamo operates in the advection-dominated regime. Experiments with more complex flow variations indicate that the shape and amplitude of flow-perturbation have no influence in the estimate of model's response time.
For the first time, the kinematic evolution of a coronal wave over the entire solar surface is studied. Full Sun maps can be made by combining images from the Solar Terrestrial Relations Observatory satellites, Ahead and Behind, and the Solar Dynamics Observatory, thanks to the wide angular separation between them. We study the propagation of a coronal wave, also known as "EIT" wave, and its interaction with a coronal hole resulting in secondary waves and/or reflection and transmission. We explore the possibility of the wave obeying the law of reflection of waves. In a detailed example we find that a loop arcade at the coronal hole boundary cascades and oscillates as a result of the EUV wave passage and triggers a wave directed eastwards that appears to have reflected. We find that the speed of this wave decelerates to an asymptotic value, which is less than half of the primary EUV wave speed. Thanks to the full Sun coverage we are able to determine that part of the primary wave is transmitted through the coronal hole. This is the first observation of its kind. The kinematic measurements of the reflected and transmitted wave tracks are consistent with a fast-mode MHD wave interpretation. Eventually, all wave tracks decelerate and disappear at a distance. A possible scenario of the whole process is that the wave is initially driven by the expanding coronal mass ejection and subsequently decouples from the driver and then propagates at the local fast-mode speed.
We have observed 3C~279 in a gamma-ray flaring state in November 2008. We construct quasi-simultaneous spectral energy distributions (SEDs) of the source for the flaring period of 2008 and during a quiescent period in May 2010. Data have been compiled from observations with Fermi, Swift, RXTE, the VLBA, and various ground-based optical and radio telescopes. The objective is to comprehend the correspondence between the flux and polarization variations observed during these two time periods by carrying out a detailed spectral analyses of 3C~279 in the internal shock scenario, and gain insights into the role of intrinsic parameters and interplay of synchrotron and inverse Compton radiation processes responsible for the two states. As a first step, we have used a multi-slice time-dependent leptonic jet model, in the framework of the internal shock scenario, with radiation feedback to simulate the SED of 3C~279 observed in an optical high state in early 2006. We have used physical jet parameters obtained from the VLBA monitoring to guide our modeling efforts. We briefly discuss the effects of intrinsic parameters and various radiation processes in producing the resultant SED.
We present a scheme for numerical simulations of collisionless self-gravitating systems which directly integrates the Vlasov--Poisson equations in six-dimensional phase space. By the results from a suite of large-scale numerical simulations, we demonstrate that the present scheme can simulate collisionless self-gravitating systems properly. The integration scheme is based on the positive flux conservation method recently developed in plasma physics. We test the accuracy of our code by performing several test calculations including the stability of King spheres, the gravitational instability and the Landau damping. We show that the mass and the energy are accurately conserved for all the test cases we study. The results are in good agreement with linear theory predictions and/or analytic solutions. The distribution function keeps the property of positivity and remains non-oscillatory. The largest simulations are run on 64^6 grids. The computation speed scales well with the number of processors, and thus our code performs efficiently on massively parallel supercomputers.
We report on radiation properties of extreme nulling pulsar J1502-5653, by analyzing the data acquired from the Parkes 64-m telescope at 1374 MHz. The radio emission from this pulsar exhibits sequences of several tens to several hundreds consecutive burst pulses, separated by null pulses, and the appearance of the emission seems quasi-periodic. The null fraction from the data is estimated to be 93.6%. No emission is detected in the integrated profile of all null pulses. Systematic modulations of pulse intensity and phase are found at the beginning of burst-pulse sequences just after null. The intensity usually rises to a maximum for the first few pulses, then declines exponentially afterwards, and becomes stable after few tens of pulse periods. The peak phase appears at later longitudes for the first pulse, then drifts to earlier longitudes rapidly, and then systematic drifting gradually vanishes while the intensity becomes stable. In this pulsar, the intensity variation and phase modulation of pulses are correlated in a short duration after the emission starts following a null. Observed properties of the pulsar are compared with other nulling pulsars published previously, and the possible explanation for phase modulation is discussed.
We present a constrained formulation of Dedner et al's hyperbolic/parabolic divergence cleaning scheme for enforcing the \nabla\dot B = 0 constraint in Smoothed Particle Magnetohydrodynamics (SPMHD) simulations. The constraint we impose is that energy removed must either be conserved or dissipated, such that the scheme is guaranteed to decrease the overall magnetic energy. This is shown to require use of conjugate numerical operators for evaluating \nabla\dot B and \nabla{\psi} in the SPMHD cleaning equations. The resulting scheme is shown to be stable at density jumps and free boundaries, in contrast to an earlier implementation by Price & Monaghan (2005). Optimal values of the damping parameter are found to be {\sigma} = 0.2-0.3 in 2D and {\sigma} = 0.8-1.2 in 3D. With these parameters, our constrained Hamiltonian formulation is found to provide an effective means of enforcing the divergence constraint in SPMHD, typically maintaining average values of h |\nabla\dot B| / |B| to 0.1-1%, up to an order of magnitude better than artificial resistivity without the associated dissipation in the physical field. Furthermore, when applied to realistic, 3D simulations we find an improvement of up to two orders of magnitude in momentum conservation with a corresponding improvement in numerical stability at essentially zero additional computational expense.
The U.S. Virtual Astronomical Observatory (VAO) is a product-driven organization that provides new scientific research capabilities to the astronomical community. Software development for the VAO follows a lightweight framework that guides development of science applications and infrastructure. Challenges to be overcome include distributed development teams, part-time efforts, and highly constrained schedules. We describe the process we followed to conquer these challenges while developing Iris, the VAO application for analysis of 1-D astronomical spectral energy distributions (SEDs). Iris was successfully built and released in less than a year with a team distributed across four institutions. The project followed existing International Virtual Observatory Alliance inter-operability standards for spectral data and contributed a SED library as a by-product of the project. We emphasize lessons learned that will be folded into future development efforts. In our experience, a well-defined process that provides guidelines to ensure the project is cohesive and stays on track is key to success. Internal product deliveries with a planned test and feedback loop are critical. Release candidates are measured against use cases established early in the process, and provide the opportunity to assess priorities and make course corrections during development. Also key is the participation of a stakeholder such as a lead scientist who manages the technical questions, advises on priorities, and is actively involved as a lead tester. Finally, frequent scheduled communications (for example a bi-weekly tele-conference) assure issues are resolved quickly and the team is working toward a common vision
Gravitational waves carry unique information about high-energy astrophysical events such as the inspiral and merger of neutron stars and black holes, core collapse in massive stars, and other sources. Large gravitational wave (GW) detectors utilizing exquisitely sensitive laser interferometry--namely, LIGO in the United States and GEO 600 and Virgo in Europe--have been successfully operated in recent years and are currently being upgraded to greatly improve their sensitivities. Many signals are expected to be detected in the coming decade. Simultaneous observing with the network of GW detectors enables us to identify and localize event candidates on the sky with modest precision, opening up the possibility of capturing optical transients or other electromagnetic counterparts to confirm an event and obtain complementary information about it. We developed and implemented the first complete low-latency GW data analysis and alert system in 2009-10 and used it to send alerts to several observing partners; the system design and some lessons learned are briefly described. We discuss several operational considerations and design choices for improving this scientific capability for future observations.
In the attempt to explain luminosity distance observations it has been proposed that we may be inside a local inhomogeneity whose effects could be equivalent to the presence of a cosmological constant in a homogeneous Universe. Using a local Taylor expansion method we study the low-redshift conditions to obtain an apparent negative deceleration parameter $q^{app}(z)$ derived from the luminosity distance $D_L(z)$ for a central observer in a LTB space. We calculate $q^{app}(z)$ with two different methods to solve the null geodesic equations, one based on a local central expansion of the solution in terms of cosmic time and the other one using the exact analytical solution in terms of generalized conformal time. The expansion of the solution in terms of cosmic time is quite useful also for other applications requiring a foliation of space-time in space-like hyper-surfaces, such as spatial averaging, which is much more difficult to study using conformal time.
We forecast combined future constraints from the cosmic microwave background and large-scale structure on the models of primordial non-Gaussianity. We study the generalized local model of non-Gaussianity, where the parameter f_NL is promoted to a function of scale, and present the principal component analysis applicable to an arbitrary form of f_NL(k). We emphasize the complementarity between the CMB and LSS by using Planck, DES and BigBOSS surveys as examples, forecast constraints on the power-law f_NL(k) model, and introduce the figure of merit for measurements of scale-dependent non-Gaussianity.
Massive black holes have been discovered in all closely examined galaxies with high velocity dispersion. The case is not as clear for lower-dispersion systems such as low-mass galaxies and globular clusters. Here we suggest that above a critical velocity dispersion of roughly 40 km/s, massive central black holes will form in relaxed stellar systems at any cosmic epoch. This is because above this dispersion primordial binaries cannot support the system against deep core collapse. If, as previous simulations show, the black holes formed in the cluster settle to produce a dense subcluster, then given the extremely high densities reached during core collapse the holes will merge with each other. For low velocity dispersions and hence low cluster escape speeds, mergers will typically kick out all or all but one of the holes due to three-body kicks or the asymmetric emission of gravitational radiation. If one hole remains, it will tidally disrupt stars at a high rate. If none remain, one is formed after runaway collisions between stars, then it tidally disrupts stars at a high rate. The accretion rate after disruption is many orders of magnitude above Eddington. If, as several studies suggest, the hole can accept matter at that rate because the generated radiation is trapped and advected, then it will grow quickly and form a massive central black hole.
Mutually uncorrelated random discrete events, manifesting a common basic process, are examined often in terms of their occurrence rate as a function of one or more of their distinguishing attributes, such as measurements of photon spectrum as a function of energy. Such rate distributions obtained from the observed attribute values for an ensemble of events will correspond to the "true" distribution only if the event occurrence were {\it mutually exclusive}. However, due to finite resolution in such measurements, the problem of event {\it pile-up} is not only unavoidable, but also increases with event rate. Although extensive simulations to estimate the distortion due to pile-up in the observed rate distribution are available, no restoration procedure has yet been suggested. Here we present an elegant analytical solution to recover the underlying {\it true} distribution. Our method, based on Poisson statistics and Fourier transforms, is shown to perform as desired even when applied to distributions that are significantly distorted by pile-up. Our recipes for correction, as well as for prediction, of pile-up are expected to find ready applications in a wide variety of fields, ranging from high-energy physics to medical clinical diagnostics, and involving, but not limited to, measurements of count-rates and/or spectra of incident radiation using Charge Coupled Devices (CCDs) or other similar devices.
The Universe has a gravitational horizon, coincident with the Hubble sphere, that plays an important role in how we interpret the cosmological data. Recently, however, its significance as a true horizon has been called into question, even for cosmologies with an equation-of-state w = p/rho > -1, where p and rho are the total pressure and energy density, respectively. The claim behind this argument is that its radius R_h does not constitute a limit to our observability when the Universe contains phantom energy, i.e., when w < -1, as if somehow that mitigates the relevance of R_h to the observations when w > -1. In this paper, we reaffirm the role of R_h as the limit to how far we can see sources in the cosmos, regardless of the Universe's equation of state, and point out that claims to the contrary are simply based on an improper interpretation of the null geodesics.
We report the detection of the orbital velocity of non-transiting hot Jupiter Tau Boo b. By employing high-resolution ground-based spectroscopy around 2.3 {\mu}m during one half night, we are able to detect carbon monoxide absorption lines produced in the planet atmosphere, which shift significantly in wavelength during the course of the observations due to the orbital motion of the planet. This detection of the planetary signal results in the determination of the orbital inclination being i = 47 (+7, -6) degrees and furthermore allow us to solve for the exact planetary mass being mp = 5.6 (0.7) MJup. This clearly confirms the planetary nature of the non-transiting companion to Tau Boo.
A sample of 427 gamma-ray bursts from a database (February 2002 - April 2008) of the RHESSI satellite is analyzed statistically. The spectral lags and peak-count rates, which have been calculated for the first time in this paper, are studied completing an earlier analysis of durations and hardness ratios. The analysis of the RHESSI database has already inferred the existence of a third group with intermediate duration, apart from the so-called short and long groups. First aim of this article is to discuss the properties of these intermediate-duration bursts in terms of peak-count rates and spectral lags. Second aim is to discuss the number of GRB groups using another statistical method and by employing the peak-count rates and spectral lags as well. The standard parametric (model-based clustering) and non-parametric (K-means clustering) statistical tests together with the Kolmogorov-Smirnov and Anderson-Darling tests are used. Two new results are obtained: A. The intermediate-duration group has similar properties to the group of short bursts. Intermediate and long groups appear to be different. B. The intermediate-duration GRBs in the RHESSI and Swift databases seem to be represented by different phenomena.
CRAB pulsar data has been parameterized by using exponential function or broken exponential function. we use non extensive form of exponential function to parameterize this data.
I shall review what has been learnt during 20 years of lithium observations in stars belonging to metal-poor globular clusters. The focus will be on little evolved main-sequence, turnoff-point (TOP) and subgiant-branch (SGB) stars expected to display Spite-plateau lithium abundances like those found in the majority of field stars of similar metallicities. But is the Spite plateau of globular clusters the same as those of field stars? What effect does, e.g., cluster-internal pollution have on lithium abundances in the now dominant second generation of stars? It will be shown that it is primarily our incomplete knowledge of the temperature scale of Population II stars which currently limits the diagnostic power of globular clusters as regards the stellar-surface evolution of lithium.
General Relativity is able to describe the dynamics of galaxies and larger cosmic structures only if most of the matter in the Universe is dark, namely it does not emit any electromagnetic radiation. Intriguingly, on the scale of galaxies, there is strong observational evidence that the presence of dark matter appears to be necessary only when the gravitational field inferred from the distribution of the luminous matter falls below an acceleration of the order of 10^(-10) m/s^2. In the standard model, which combines Newtonian gravity with dark matter, the origin of this acceleration scale is challenging and remains unsolved. On the contrary, the full set of observations can be neatly described, and were partly predicted, by a modification of Newtonian dynamics, dubbed MOND, that does not resort to the existence of dark matter. On the scale of galaxy clusters and beyond, however, MOND is not as successful as on the scale of galaxies, and the existence of some dark matter appears unavoidable. A model combining MOND with hot dark matter made of sterile neutrinos seems to be able to describe most of the astrophysical phenomenology, from the power spectrum of the cosmic microwave background anisotropies to the dynamics of dwarf galaxies. Whether there exists a yet unknown covariant theory that contains General Relativity and Newtonian gravity in the weak field limit, and MOND as the ultra-weak field limit is still an open question.
The paper presents a sample of newly detected eclipsing binaries from the public Kepler data. Orbits and fundamental parameters of 20 unknown eclipsing binaries were determined by modeling of their photometric data. Most of them are well-detached, high-eccentric binaries. We established that the target KID8552719 satisfied all widespread criteria for a planetary candidate. Fitting its light curve we obtained radius R_p=0.9 R_Nept, distance to the host star a = 42.58 Rsun = 0.198 AU and equilibrium temperatute T_p= 489 K. These values imply a Neptune-size object out of the habitable zone of the host star.
HD 327083 is a sgB[e] star that forms a binary system with an orbital semi-major axis of ~1.7 AU. Our previous observations using the VLTI and AMBER in the medium resolution K-band mode spatially resolved the environment of HD 327083. The continuum visibilities obtained indicate the presence of a circumbinary disc. CO bandhead emission was also observed. However, due to the limited spectral resolution of the previous observations, the kinematic structure of the emitting material was not constrained. In this paper, we address this and probe the source of the CO emission with high spectral resolution and spatial precision. We have observed HD 327083 with high spectral resolution (25 & 6 km/s) using AMBER and CRIRES. The observations are compared to kinematical models to constrain the source of the emission. It is shown that the CO bandhead emission can be reproduced using a model of a Keplerian disc with an inclination and size consistent with our previous VLTI observations. The model is compared to AMBER differential phase measurements, which have a precision as high as 30-micro-arcseconds. A differential phase signal corresponding to 0.15 milli-arcseconds (~5 sigma) is seen over the bandhead emission, which is in excellent agreement with the model that fits the CRIRES observations. In comparison, a model of an equatorial outflow, as envisaged in the standard sgB[e] scenario, does not reproduce the observations well. The excellent agreement between the disc model and observations in the spatial and spectral domains is compelling evidence that the CO bandhead emission of HD 327083 originates in a circumbinary Keplerian disc. In contrast, the model of an equatorial outflow cannot reproduce the observations well. This suggests that the standard sgB[e] scenario is not applicable to HD 327083, which supports the hypothesis that the B[e] behaviour of HD 327083 is due to binarity (ABRIDGED).
In astrophysical systems, radiation-matter interactions are important in transferring energy and momentum between the radiation field and the surrounding material. This coupling often makes it necessary to consider the role of radiation when modelling the dynamics of astrophysical fluids. During the last few years, there have been rapid developments in the use of Monte Carlo methods for numerical radiative transfer simulations. Here, we present an approach to radiation hydrodynamics that is based on coupling Monte Carlo radiative transfer techniques with finite-volume hydrodynamical methods in an operator-split manner. In particular, we adopt an indivisible packet formalism to discretize the radiation field into an ensemble of Monte Carlo packets and employ volume-based estimators to reconstruct the radiation field characteristics. In this paper the numerical tools of this method are presented and their accuracy is verified in a series of test calculations. Finally, as a practical example, we use our approach to study the influence of the radiation-matter coupling on the homologous expansion phase and the bolometric light curve of Type Ia supernova explosions.
We present IACTalks, a free and open access seminars archive (this http URL) aimed at promoting astronomy and the exchange of ideas by providing high-quality scientific seminars to the astronomical community. The archive of seminars and talks given at the Instituto de Astrofi\'isica de Canarias goes back to 2008. Over 360 talks and seminars are now freely available by streaming over the internet. We describe the user interface, which includes two video streams, one showing the speaker, the other the presentation. A search function is available, and seminars are indexed by keywords and in some cases by series, such as special training courses or the 2011 Winter School of Astrophysics, on secular evolution of galaxies. The archive is made available as an open resource, to be used by scientists and the public.
Atmospheric escape has been detected from the exoplanet HD 209458b through
transit observations of the hydrogen Lyman-alpha line. Here we present
spectrally resolved Lyman-alpha transit observations of the exoplanet HD
189733b at two different epochs. These HST/STIS observations show for the first
time, that there are significant temporal variations in the physical conditions
of an evaporating planetary atmosphere. While atmospheric hydrogen is not
detected in the first epoch observations, it is observed at the second epoch,
producing a transit absorption depth of 14.4+/-3.6% between velocities of -230
to -140 km/s. Contrary to HD 209458b, these high velocities cannot arise from
radiation pressure alone and require an additional acceleration mechanism, such
as interactions with stellar wind protons. The observed absorption can be
explained by an atmospheric escape rate of neutral hydrogen atoms of about 10^9
g/s, a stellar wind with a velocity of 190 km/s and a temperature of ~10^5K.
An X-ray flare from the active star seen with Swift/XRT 8 hours before the
second-epoch observation supports the idea that the observed changes within the
upper atmosphere of the planet can be caused by variations in the stellar wind
properties, or by variations in the stellar energy input to the planetary
escaping gas (or a mix of the two effects). These observations provide the
first indication of interaction between the exoplanet's atmosphere and stellar
variations.
We present basic atmospheric parameters (Teff, logg, vt and [Fe/H]) as well as luminosities, masses, radii and absolute radial velocities for 348 stars, presumably giants, from the ~1000 star sample observed within the Penn State-Torun Centre for Astronomy Planet Search with the High Resolution Spectrograph of the 9.2m Hobby-Eberly Telescope. The stellar parameters are key ingredients in proper interpretation of newly discovered low-mass companions while a systematic study of the complete sample will create a basis for future statistical considerations concerning low-mass companions appearance around evolved low and intermediate-mass stars. The atmospheric parameters were derived using a strictly spectroscopic method based on the LTE analysis of equivalent widths of FeI and FeII lines. With existing photometric data and the Hipparcos parallaxes we estimated stellar masses and ages via evolutionary tracks fitting. The stellar radii were calculated from either estimated masses and the spectroscopic logg or from the spectroscopic Teff and estimated luminosities. The absolute radial velocities were obtained by cross-correlating spectra with a numerical template. We completed the spectroscopic analysis for 332 stars of which 327 were found to be giants. For the remaining 16 stars with incomplete data a simplified analysis was applied. The results show that our sample is composed of stars with Teff = 4055-6239 K, logg = 1.39-4.78 (5 dwarfs were identified), logL/Lo = -1.0-3, M = 0.6-3.4 Mo, R = 0.6-52 Ro. The stars in our sample are generally less metal abundant than the Sun with median [Fe/H] = -0.15. The estimated uncertainties in the atmospheric parameters were found to be comparable to those reached in other studies. However, due to lack of precise parallaxes the stellar luminosities and, in turn, the masses are far less precise, within 0.2 Mo in best cases, and 0.3 Mo on average.
The MOJAVE survey contains 101 quasars with a total of 354 observed radio
components that are different from the radio cores, among which 95% move with
apparent projected superluminal velocities with respect to the core, and 45%
have projected velocities larger than 10c (with a maximum velocity 60c).
Doppler boosting effects are analyzed to determine the statistics of the
superluminal motions. We integrate over all possible values of the Lorentz
factor the values of the kinetic energy corresponding to each component. The
calculation of the mass in the ejection is carried out by assuming the minimum
energy state. This kinetic energy is multiplied by the frequency at which the
portions of the jet fluid identified as "blobs" are produced. Hence, we
estimate the average total power released by the quasars in the form of kinetic
energy in the long term on pc-scales.
RESULTS. A selection effect in which both the core and the blobs of the
quasar are affected by huge Doppler-boosting enhancement increases the
probability of finding a jet ejected within 10 degrees of the line of sight
>~40 times above what one would expect for a random distribution of ejection,
which explains the ratios of the very high projected velocities given above.
The average total kinetic power of each MOJAVE quasar should be very high to
obtain this distribution: ~7E47 erg/s. This amount is much higher than previous
estimates of kinetic power on kpc-scales based on the analysis of cavities in
X-ray gas or radio lobes in samples of objects of much lower radio luminosity
but similar black hole masses. The kinetic power is a significant portion of
the Eddington luminosity, on the order of the bolometric luminosity, and
proportional on average to square root of the radio luminosity, although this
correlation might be induced by Malmquist-like bias.
The worldwide race towards direct dark matter detection in the form of Weakly Interacting Massive Particles (WIMPs) has been dramatically accelerated by the remarkable progress and evolution of liquid xenon time projection chambers (LXeTPCs). With a realistic discovery potential, XENON100 has already reached a sensitivity of $7\times10^{-45}\,\n{cm}^2$, and continues to accrue data at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy towards its ultimate sensitivity reach at the $\sigma_{\n{SI}}\sim 2\times10^{-45}\,\n{cm}^2$ level for the spin-independent WIMP-nucleon cross-section. To fully explore the favoured parameter space for WIMP dark matter in search of a first robust and statistically significant discovery, or to confirm any hint of a signal from \Xehund, the next phase of the XENON program will be a detector at the ton scale - XENON1T. The XENON1T detector, based on 2.2 ton of LXe viewed by low radioactivity photomultiplier tubes and housed in a water Cherenkov muon veto at LNGS, is presented. With an experimental aim of probing WIMP interaction cross-sections above of order $\sigma_{\n{SI}}\sim 2\times10^{-47}\,\n{cm}^2$ within 2 years of operation, XENON1T will provide the sensitivity to probe a particularly favourable region of electroweak physics on a timescale compatible with complementary ground and satellite based indirect searches and with accelerator dark matter searches at the LHC. Indeed, for a $\sigma_{\n{SI}} \sim 10^{-45}\,\n{cm}^2$ and $100 \,\n{GeV/c^2}$ WIMP mass, XENON1T could detect of order 100 events in this exposure, providing statistics for placing significant constraints on the WIMP mass.
The analysis of Type Ia supernova data over the past decade has provided one of the most notable success stories in cosmology. Arguably the most reliable standard candles we have to date, they offer us an unparalleled opportunity of studying the cosmological expansion out to a redshift of ~1.5. The consensus today appears to be that LCDM offers the best explanation for the luminosity-distance relationship seen in these events. However, a significant incompatibility is now emerging between the standard model and other equally important observations, such as those of the cosmic microwave background. These studies indicate that LCDM does not provide an accurate representation of the cosmological expansion at high redshifts (z >> 2). It has therefore become essential to re-analyze the Type Ia supernova data in light of the cosmology (the R_h=ct Universe) that best represents the Universe's dynamical evolution at early times. In this paper, we directly compare the distance-relationship in LCDM with that predicted by the R_h=ct Universe, and each with the Union2.1 sample, and show that the two theories produce virtually indistinguishable profiles. In so doing, we directly address recent criticisms of the R_h=ct cosmology based on analysis of the Type Ia supernova observations. We suggest that fitting the data with LCDM compels it to relax to the R_h=ct Universe, which has no free parameters. However, we also highlight the fact that the data cannot be determined independently of the assumed cosmology, because the supernova luminosities must be evaluated by optimizing 4 parameters simultaneously with those in the adopted model. This renders the data compliant to the underlying theory, suggesting that one should not ignore the model-dependent data reduction in any comparative analysis between competing cosmologies.
The Gaia-ESO Survey is a wide field spectroscopic survey recently started with the FLAMES@VLT in Cerro Paranal, Chile. It will produce radial velocities more accurate than Gaia's for faint stars (down to V~18), and astrophysical parameters and abundances for approximately 100000 stars, belonging to all Galactic populations. 300 nights were assigned in 5 years (with the last year subject to approval after a detailed report). In particular, to connect with other ongoing and planned spectroscopic surveys, a detailed calibration program --- for the astrophysical parameters derivation --- is planned, including well known clusters, Gaia benchmark stars, and special equatorial calibration fields designed for wide field/multifiber spectrographs.
The purpose of this work is to make available new gas-phase oxygen abundance measurements for a serendipitous sample of 27 galaxies with redshift 0.35\leqz\leq0.52. We measured the equivalent widths of the [O II]{\lambda}3727, H{\beta}, and [O III]{\lambda}{\lambda}4959, 5007 emission lines observed in the galaxy spectra obtained with the Visible Multi-Object Spectrograph mounted at the Very Large Telescope. For each galaxy, we derived the metallicity-sensitive emission lines ratio R23, ionization-sensitive emission lines ratio O32, and gas-phase oxygen abundance 12+log(O/H). The values of gas-phase oxygen abundance 12+log(O/H) we obtained for the sample galaxies are consistent with previous findings for galaxies at intermediate redshift.
Detections of molecular lines, mainly from H2$ and CO, reveal molecular material in planetary nebulae. Observations of a variety of molecules suggest that the molecular composition in these objects differs from that found in interstellar clouds or in circumstellar envelopes. The success of the models, which are mostly devoted to explain molecular densities in specific planetary nebulae, is still partial, however. The present study aims at identifying the influence of stellar and nebular properties on the molecular composition of planetary nebulae by means of chemical models. A comparison of theoretical results with those derived from the observations may provide clues to the conditions that favor the presence of a particular molecule. A self-consistent photoionization numerical code was adapted to simulate cold molecular regions beyond the ionized zone. The code was used to obtain a grid of models and the resulting column densities are compared with those inferred from observations. Our models show that the inclusion of an incident flux of X-rays is required to explain the molecular composition derived for planetary nebulae. We also obtain a more accurate relation for the N(CO)/N(H2) ratio in these objects. Molecular masses obtained by previous works in the literature were then recalculated, showing that these masses can be underestimated by up to three orders of magnitude. We conclude that the problem of the missing mass in planetary nebulae can be solved by a more accurate calculation of the molecular mass.
The formation, composition and physical properties of lunar dust are incompletely characterised with regard to human health. While the physical and chemical determinants of dust toxicity for materials such as asbestos, quartz, volcanic ashes and urban particulate matter have been the focus of substantial research efforts, lunar dust properties, and therefore lunar dust toxicity may differ substantially. In this contribution, past and ongoing work on dust toxicity is reviewed, and major knowledge gaps that prevent an accurate assessment of lunar dust toxicity are identified. Finally, a range of studies using ground-based, low-gravity, and in situ measurements is recommended to address the identified knowledge gaps. Because none of the curated lunar samples exist in a pristine state that preserves the surface reactive chemical aspects thought to be present on the lunar surface, studies using this material carry with them considerable uncertainty in terms of fidelity. As a consequence, in situ data on lunar dust properties will be required to provide ground truth for ground-based studies quantifying the toxicity of dust exposure and the associated health risks during future manned lunar missions.
Direct imaging of circumstellar disks at high angular resolution is mandatory to provide morphological information that bring constraints on their properties, in particular the spatial distribution of dust. New techniques combining observing strategy and data processing now allow very high contrast imaging with 8-m class ground-based telescopes (10^-4 to 10^-5 at ~1") and complement space telescopes while improving angular resolution at near infrared wavelengths. We carried out a program at the VLT with NACO to image known debris disks with higher angular resolution in the near IR than ever before in order to study morphological properties and ultimately to detect signpost of planets. The observing method makes use of advanced techniques: Adaptive Optics, Coronagraphy and Differential Imaging, a combination designed to directly image exoplanets with the upcoming generation of "planet finders" like GPI (Gemini Planet Imager) and SPHERE (Spectro-Polarimetric High contrast Exoplanet REsearch). Applied to extended objects like circumstellar disks, the method is still successful but produces significant biases in terms of photometry and morphology. We developed a new model-matching procedure to correct for these biases and hence to bring constraints on the morphology of debris disks. From our program, we present new images of the disk around the star HD 32297 obtained in the H (1.6mic) and Ks (2.2mic) bands with an unprecedented angular resolution (~65 mas). The images show an inclined thin disk detected at separations larger than 0.5-0.6". The modeling stage confirms a very high inclination (i=88{\deg}) and the presence of an inner cavity inside r_0~110AU. We also found that the spine (line of maximum intensity along the midplane) of the disk is curved and we attributed this feature to a large anisotropic scattering factor (g~0.5, valid for an non-edge on disk). Abridged ...
Far ultraviolet emission has been detected from a knot of Halpha emission in the Horseshoe filament, far out in the NGC 1275 nebula. The flux detected relative to the brightness of the Halpha line in the same spatial region is very close to that expected from Hydrogen two-photon continuum emission in the particle heating model of Ferland et al. (2009) if reddening internal to the filaments is taken into account. We find no need to invoke other sources of far ultraviolet emission such as hot stars or emission lines from CIV in intermediate temperature gas to explain these data.
We study plasma flows above pulsar polar caps using time-dependent simulations of plasma particles in the self-consistent electric field. The flow behavior is controlled by dimensionless parameter alpha, the ratio of electric current density j to Goldreich-Julian current c\rho_GJ. The region of the polar cap where 0<alpha<1 is a "dead zone" -- in this zone particle acceleration is inefficient and pair creation is not expected even for young, rapidly rotating pulsars. Pulsars with polar caps near the rotation axis are predicted to have a hollow-cone structure of radio emission, as the dead zone occupies the central part of the polar cap. Our results apply to charge-separated flows of electrons (j<0) or ions (j>0). In the latter case, we consider the possibility of a mixed flow consisting of different ion species, and observe the development of two-stream instability. The dead zone at the polar cap is essential for activation of an outer gap that is associated with the null surface \rho_GJ=0.
Eclipsing binaries (EBs) provide critical laboratories for empirically testing predictions of theoretical models of stellar structure and evolution. Pre-main-sequence (PMS) EBs are particularly valuable, both due to their rarity and the highly dynamic nature of PMS evolution, such that a dense grid of PMS EBs is required to properly calibrate theoretical PMS models. Analyzing multi-epoch, multi-color light curves for 2400 candidateOrion Nebula Cluster (ONC) members from our Warm Spitzer Exploration Science Program YSOVAR, we have identified 12 stars whose light curves show eclipse features. Four of these 12 EBs are previously known. Supplementing our light curves with follow-up optical and near-infrared spectroscopy, we establish two of the candidates as likely field EBs lying behind the ONC. We confirm the remaining six candidate systems, however, as newly identified ONC PMS EBs. These systems increase the number of known PMS EBs by over 50% and include the highest mass (Theta1 Ori E, for which we provide a complete set of well-determined parameters including component masses of 2.807 and 2.797 solar masses) and longest period (ISOY J053505.71-052354.1, P \sim 20 days) PMS EBs currently known. In two cases (Theta1 Ori E and ISOY J053526.88-044730.7), enough photometric and spectroscopic data exist to attempt an orbit solution and derive the system parameters. For the remaining systems, we combine our data with literature information to provide a preliminary characterization sufficient to guide follow-up investigations of these rare, benchmark systems.
Assessing the impact of astronomical facilities rests upon an evaluation of the scientific discoveries which their data have enabled. Telescope bibliographies, which link data products with the literature, provide a way to use bibliometrics as an impact measure for the underlying data. In this paper we argue that the creation and maintenance of telescope bibliographies should be considered an integral part of an observatory's operations. We review the existing tools, services, and workflows which support these curation activities, giving an estimate of the effort and expertise required to maintain an archive-based telescope bibliography.
The nearby (d = 7.7 pc) A3V star Fomalhaut is orbited by a resolved dusty debris disk and a controversial candidate extrasolar planet. The commonly cited age for the system (200+-100 Myr) from Barrado y Navascues et al. (1997) relied on a combination of isochronal age plus youth indicators for the K4V common proper motion system TW PsA. TW PsA is 1.96 deg away from Fomalhaut, and was first proposed as a companion by Luyten (1938), but the physicality of the binarity is worth testing with modern data. I demonstrate that TW PsA is unequivocably a physical stellar companion to Fomalhaut, with true separation 0.280+0.019-0.012 pc (57.4+3.9-2.5 kAU) and sharing velocities within 0.1+-0.3 km/s -- consistent with being a bound system. Hence, TW PsA should be considered "Fomalhaut B". Combining modern HR diagram constraints with four sets of evolutionary tracks, and assuming the star was born with protosolar composition, I estimate a new isochronal age for Fomalhaut of 450+-40 Myr and mass of 1.92+-0.02 Msun. Various stellar youth diagnostics are re-examined for TW PsA. The star's rotation, X-ray emission, and Li abundances are consistent with approximate ages of 410, 380, and 360 Myr, respectively, yielding a weighted mean age of 400+-70 Myr. Combining the independent ages, I estimate a mean age for the Fomalhaut-TW PsA binary of 440+-40 Myr. The older age implies that substellar companions of a given mass are approximately one magnitude fainter at IR wavelengths than previously assumed.
We present Herschel PACS photometry of seventeen B- to M-type stars in the 30 Myr-old Tucana-Horologium Association. This work is part of the Herschel Open Time Key Programme "Gas in Protoplanetary Systems" (GASPS). Six of the seventeen targets were found to have infrared excesses significantly greater than the expected stellar IR fluxes, including a previously unknown disk around HD30051. These six debris disks were fitted with single-temperature blackbody models to estimate the temperatures and abundances of the dust in the systems. For the five stars that show excess emission in the Herschel PACS photometry and also have Spitzer IRS spectra, we fit the data with models of optically thin debris disks with realistic grain properties in order to better estimate the disk parameters. The model is determined by a set of six parameters: surface density index, grain size distribution index, minimum and maximum grain sizes, and the inner and outer radii of the disk. The best fitting parameters give us constraints on the geometry of the dust in these systems, as well as lower limits to the total dust masses. The HD105 disk was further constrained by fitting marginally resolved PACS 70 micron imaging.
One of the greatest problems of primordial inflation is that the inflationary space-time is past-incomplete. This is mainly because Einstein's GR suffers from a space-like Big Bang singularity. It has recently been shown that ghost-free, non-local higher-derivative ultra-violet modifications of Einstein's gravity may be able to resolve the cosmological Big Bang singularity via a non-singular bounce. Within the framework of such non-local cosmological models, we are going to study both sub- and super-Hubble perturbations around an inflationary trajectory which is preceded by the Big Bounce in the past, and demonstrate that the inflationary trajectory has an ultra-violet completion and that perturbations do not suffer from any pathologies.
We present time-series photometry of two fields near M32 using archival observations from ACS/WFC onboard HST. One field is centered about 2 arcmin from M32 while the other is located 15 arcmin to the southeast of M31. We identify a total of 1139 RR Lyrae variables of which 821 are ab-type and 318 are c-type. In the field near M32, we find a radial gradient in the density of RR Lyraes relative to the center of M32. This gradient is consistent with the surface brightness profile of M32 suggesting that a significant number of the RR Lyraes in this region belong to M32. This provides further confirmation that M32 contains an ancient stellar population formed around the same time as the oldest population in M31 and the Milky Way. The RR Lyrae stars in M32 exhibit a mean metal abundance of [Fe/H] ~ -1.42 +/- 0.02, which is ~15 times lower than the metal abundance of the overall M32 stellar population. Moreover, the abundance of RR Lyrae stars normalized to the luminosity of M32 in the field analyzed further indicates that the ancient metal-poor population in M32 represents only a very minor component of this galaxy, consistent with the 1% to 4.5% in mass inferred from the CMD analysis of Monachesi et al. In the other field, we find unprecedented evidence for two populations of RR Lyraes in M31 as shown by two distinct sequences among the ab-type variables in the Bailey Diagram. When interpreted in terms of metal abundance, one population exhibits a peak at [Fe/H] ~ -1.3 and the other is at [Fe/H] ~ -1.9. One possible interpretation of this result is that the more metal-rich population represents the dominant M31 halo, while the metal-poorer group could be a disrupted dwarf satellite galaxy orbiting M31. If true, this represents a further indication that the formation of the M31 spheroid has been significantly influenced by the merger and accretion of dwarf galaxy satellites. [abridged]
Reaction cross sections of 169Tm(alpha,gamma)173Lu and 169Tm(alpha,n)172Lu have been measured in the energy range 12.6<=E_alpha<=17.5 MeV and 11.5<=E_alpha<=17.5 MeV, respectively, using the recently introduced method of combining activation with X-ray counting. Improved shielding allowed to measure the (alpha,gamma) to lower energy than previously possible. The combination of (alpha,gamma) and (alpha,n) data made it possible to study the energy dependence of the alpha width. While absolute value and energy dependence are perfectly reproduced by theory at energies above 14 MeV, the observed change in energy dependence at energies below 14 MeV requires a modification of the predicted alpha width. Using an effective, energy-dependent, local optical alpha+nucleus potential it is possible to reproduce the data but the astrophysical rate is still not well constrained at gamma-process temperatures. The additional uncertainty stemming from a possible modification of the compound formation cross section is discussed. Including the remaining uncertainties, the recommended range of astrophysical reaction rate values at 2 GK is higher than the previously used values by factors of 2-37.
We derive a stationary and axisymmetric black hole solution to quadratic order in the spin angular momentum. The previously found, linear-in-spin terms modify the odd-parity sector of the metric, while the new corrections appear in the even-parity sector. These corrections modify the quadrupole moment, as well as the (coordinate-dependent) location of the event horizon and the ergoregion. Although the linear-in-spin metric is of Petrov type D, the quadratic order terms render it of type I, and thus, the metric does not possess a second-order Killing tensor or a Carter-like constant. The new metric does not possess closed timelike curves or spacetime regions that violate causality outside of the event horizon. The new, even-parity modifications to the Kerr metric decay less rapidly at spatial infinity than the leading-order in spin, odd-parity ones, and thus, the former are more important when considering black holes that are rotating moderately fast. We calculate the modifications to the Hamiltonian, binding energy and Kepler's third law. These modifications are crucial for the construction of gravitational wave templates for black hole binaries, which will enter at second post-Newtonian order, just like dissipative modifications found previously.
We show how Ho\v{r}ava-Lifshitz (HL) theory appears naturally in the Ashtekar formulation of relativity if one postulates the existence of a fermionic field playing the role of aether. The spatial currents associated with this field must be switched off for the equivalence to work. Therefore the field supplies the preferred frame associated with breaking refoliation (time diffeomorphism) invariance, but obviously the symmetry is only spontaneously broken if the field is dynamic. When Dirac fermions couple to the gravitational field via the Ashtekar variables, the low energy limit of HL gravity, recast in the language of Ashtekar variables, naturally emerges (provided the spatial fermion current identically vanishes). HL gravity can therefore be interpreted as a time-like current, or a Fermi aether, that fills space-time, with the Immirzi parameter, a chiral fermionic coupling, and the fermionic charge density fixing the value of the parameter $\lambda$ determining HL theory. This reinterpretation sheds light on some features of HL theory, namely its good convergence properties.
The pivotal point of the paper is to discuss the behavior of temperature, pressure, energy density as a function of volume along with determination of caloric EoS from following two model: $w(z)=w_{0}+w_{1}\ln(1+z)$ & $ w(z)=-1+\frac{(1+z)}{3}\frac{A_{1}+2A_{2}(1+z)}{A_{0}+2A_{1}(1+z)+A_{2}(1+z)^{2}}$. The time scale of instability for this two models is discussed. In the paper we then generalize our result and arrive at general expression for energy density irrespective of the model. The thermodynamical stability for both of the model and the general case is discussed from this viewpoint. We also arrive at a condition on the limiting behavior of thermodynamic parameter to validate the third law of thermodynamics and interpret the general mathematical expression of integration constant $U_{0}$ (what we get while integrating energy conservation equation) physically relating it to number of micro states. The constraint on the allowed values of the parameters of the models is discussed which ascertains stability of universe. The validity of thermodynamical laws within apparent and event horizon is discussed.
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The role of feedback from massive stars is believed to be a key element in the evolution of molecular clouds. We use high-resolution 3D SPH simulations to explore the dynamical effects of a single O7 star located at the centre of a molecular cloud with mass 10^4M_sun and radius 6.4pc. The initial internal structure of the cloud is characterised by its fractal dimension, D=2.0 - 2.8, and its log-normal density PDF. (i) As regards star formation, in the short term ionising feedback is positive, in the sense that star formation occurs much more quickly in gas that is compressed by the high pressure of the ionised gas. However, in the long term ionising feedback is negative, in the sense that most of the cloud is dispersed with an outflow rate of up to ~0.01M_sun/yr, on a timescale comparable with the sound-crossing time for the ionised gas (~1-2Myr), and triggered star formation is therefore limited to a few percent of the cloud's mass. (ii) As regards the morphology of the ionisation fronts (IFs) bounding the HII region and the systematics of outflowing gas, we distinguish two regimes. For low D<=2.2, the initial cloud is dominated by large-scale structures, so the neutral gas tends to be swept up into a few extended coherent shells, and the ionised gas blows out through a few large holes between these shells; we term these HII regions "shell-dominated". Conversely, for high D>=2.6, the initial cloud is dominated by small-scale structures, and these are quickly overrun by the advancing IF, thereby producing neutral pillars whilst the ionised gas blows out through a large number of small holes between the pillars; we term these HII regions "pillar-dominated". (iii) As regards the injection of bulk kinetic energy, by ~1Myr, the expansion of the HII region has delivered a rms velocity of ~6km/s; this represents less than 0.1% of the total energy radiated by the O7 star.
The ionization parameter U is potentially useful for measuring radiation
pressure feedback from massive star clusters, as it reflects the
radiation-to-gas-pressure ratio and is readily derived from mid-infrared line
ratios. We consider several effects which determine the apparent value of U in
HII regions and galaxies. An upper limit is set by the compression of gas by
radiation pressure. The pressure from stellar winds and the presence of neutral
clumps both reduce U for a given radiation intensity. The most intensely
irradiated regions are selectively dimmed by internal dust absorption of
ionizing photons, inducing observational bias on galactic scales. We explore
these effects analytically and numerically, and use them to interpret previous
observational results.
We find that radiation confinement sets the upper limit log_10 U = -1 seen in
individual regions. Unresolved starbursts display a maximum value of ~ -2.3.
While lower, this is also consistent with a large portion of their HII regions
being radiation dominated, given the different technique used to interpret
unresolved regions, and given the bias caused by dust absorption. We infer that
many individual, strongly illuminated regions cannot be dominated by stellar
winds, and that even when averaged on galactic scales, shocked wind pressures
cannot be large compared to radiation pressure. Therefore, most HII regions
cannot be adiabatic wind bubbles. Our models imply a metallicity dependence in
the physical structure and dust attenuation of radiation-dominated regions,
both of which should vary strongly across a critical metallicity of about
one-twentieth solar.
Using test-particle simulations, we investigate the temporal dependence of the two-point velocity correlation function for charged particles scattering in a time-independent spatially fluctuating magnetic field derived from a three-dimensional isotropic turbulence power spectrum. Such a correlation function allowed us to compute the spatial coefficients of diffusion both parallel and perpendicular to the average magnetic field. Our simulations confirm the dependence of the perpendicular diffusion coefficient on turbulence energy density and particle energy predicted previously by a model for early-time charged particle transport. Using the computed diffusion coefficients, we exploit the particle velocity autocorrelation to investigate the time-scale over which the particles "decorrelate" from the solution to the unperturbed equation of motion. Decorrelation time-scales are evaluated for parallel and perpendicular motions, including the drift of the particles from the local magnetic field line. The regimes of strong and weak magnetic turbulence are compared for various values of the ratio of the particle gyroradius to the correlation length of the magnetic turbulence. Our simulation parameters can be applied to energetic particles in the interplanetary space, cosmic rays at the supernova shocks, and cosmic-rays transport in the intergalactic medium.
We study the effect of baryons on the abundance of structures and substructures in a Lambda-CDM cosmology, using a pair of high resolution cosmological simulations from the GIMIC project. Both simulations use identical initial conditions, but while one contains only dark matter, the other also includes baryons. We find that gas pressure, reionisation, supernova feedback, stripping, and truncated accretion systematically reduce the total mass and the abundance of structures below ~10^12 solar masses compared to the pure dark matter simulation. Taking this into account and adopting an appropriate detection threshold lowers the abundance of observed galaxies with maximum circular velocities below 100 km/s, significantly reducing the reported discrepancy between Lambda-CDM and the measured HI velocity function of the ALFALFA survey. We also show that the stellar-to-total mass ratios of galaxies with stellar masses of ~10^5 - 10^7 solar masses inferred from abundance matching of the (sub)halo mass function to the observed galaxy mass function increase by a factor of ~2. In addition, we find that an important fraction of low-mass subhaloes are completely devoid of stars. Accounting for the presence of dark subhaloes below 10^10 solar masses further reduces the abundance of observable objects, and leads to an additional increase in the inferred stellar-to-total mass ratio by factors of 2 - 10 for galaxies in haloes of 10^9 - 10^10 solar masses. This largely reconciles the abundance matching results with the kinematics of individual dwarf galaxies in Lambda-CDM. We propose approximate corrections to the masses of objects derived from pure dark matter calculations to account for baryonic effects.
We present photometric measurements for the 769 z~0 galaxies in the first-epoch data of the Zurich Environmental Study (ZENS). The main thrust of ZENS is to study the dependence of galaxy properties on the mass of the host group M_GROUP, the group-centric distance R/R_200, and the large-scale structure overdensity delta_LSS. For the galaxies and, if possible, for their bulge and disk components, the photometric measurements consist of resolved (B-I) colors, color gradients, color dispersions, and color maps, as well as stellar masses and star-formation rates. We classify ZENS galaxies into quiescent, moderately star-forming, and strongly star-forming systems using a combination of spectral features and broad-band NUV-optical colors. This optimally distinguishes quiescent systems from dust-reddened star-forming galaxies, which contribute up to 50% to the (B-I) "red sequence" at ~10^10 Msun. Our photometric database is made available for public use in the global ZENS catalog. We study how (B-I) colors, color gradients and color dispersion of bulge-dominated and disk-dominated satellites depend on M_GROUP, R/R_200 and delta_LSS at fixed stellar mass. We find that delta_LSS does not have an impact on either the colors, the color gradients or the color scatter of either disk- or bulge-dominated satellites. The latter are rather insensitive to any environment. The strongest environmental effects are found for disk-dominated satellites with group-centric distance. At constant galaxy mass, these satellites are redder in the group cores compared with the outskirts; at M>~10^10 Msun, they also have shallower color gradients within 0.6R_200 than at larger group-centric distances. Our results support a picture where galaxies undergo a relatively fast quenching of their star formation in the outer disks on timescales <~2 Gyr, as they progressively move deeper inside the group potential.[Abridged]
We have observed 37 Infrared Dark Clouds (IRDCs), containing a total of 159 clumps, in high-density molecular tracers at 3 mm using the 22-meter ATNF Mopra Telescope located in Australia. After determining kinematic distances, we eliminated clumps that are not located in IRDCs and clumps with a separation between them of less than one Mopra beam. Our final sample consists of 92 IRDC clumps. The most commonly detected molecular lines are (detection rates higher than 8%): N2H+, HNC, HN13C, HCO+, H13CO+, HCN, C2H, HC3N, HNCO, and SiO. We investigate the behavior of the different molecular tracers and look for chemical variations as a function of an evolutionary sequence based on Spitzer IRAC and MIPS emission. We find that the molecular tracers behave differently through the evolutionary sequence and some of them can be used to yield useful relative age information. The presence of HNC and N2H+ lines do not depend on the star formation activity. On the other hand, HC3N, HNCO, and SiO are predominantly detected in later stages of evolution. Optical depth calculations show that in IRDC clumps the N2H+ line is optically thin, the C2H line is moderately optically thick, and HNC and HCO+ are optically thick. The HCN hyperfine transitions are blended, and, in addition, show self-absorbed line profiles and extended wing emission. These factors combined prevent the use of HCN hyperfine transitions for the calculation of physical parameters. Total column densities of the different molecules, except C2H, increase with the evolutionary stage of the clumps. Molecular abundances increase with the evolutionary stage for N2H+ and HCO+. The N2H+/HCO+ and N2H+/HNC abudance ratios act as chemical clocks, increasing with the evolution of the clumps.
We make a revision of the stability criteria for equatorial circular orbits, obtained from the epicyclic approximation, which is widely used in Newtonian models for axisymmetric galaxies. We find that, for the case of thin disk models, the criteria of vertical stability must be reformulated, due to the discontinuity in the gravitational field. We show that, for a model characterized by a surface mass density $\Sigma$, the necessary and sufficient condition to have vertically stable orbits is that $\Sigma>0$. On the other hand, the criteria for radial stability is the same as in thick diks, i.e. that the epicyclic frequency is positive.
We present THC: a new high-order flux-vector-splitting code for Newtonian and special-relativistic hydrodynamics designed for direct numerical simulations of turbulent flows. Our code implements a variety of different reconstruction algorithms, such as the popular weighted essentially non oscillatory and monotonicity-preserving schemes, or the more specialised bandwidth-optimised WENO scheme that has been specifically designed for the study of compressible turbulence. We show the first systematic comparison of these schemes in Newtonian physics as well as for special-relativistic flows. In particular we will present the results obtained in simulations of grid-aligned and oblique shock waves and nonlinear, large-amplitude, smooth adiabatic waves. We will also discuss the results obtained in classical benchmarks such as the double-Mach shock reflection test in Newtonian physics or the linear and nonlinear development of the relativistic Kelvin-Helmholtz instability in two and three dimensions. Finally, we study the turbulent flow induced by the Kelvin-Helmholtz instability and we show that our code is able to obtain well-converged velocity spectra, from which we benchmark the effective resolution of the different schemes.
Study of cosmic dust and planetary aerosols indicate that some of them contain a large number of aggregates of the size that significantly exceeds the wavelengths of the visible light. In some cases such large aggregates may dominate in formation of the light scattering characteristics of the dust. In this paper we present the results of computer modelling of light scattering by aggregates that contain more than 1000 monomers of submicron size and study how their light scattering characteristics, specifically polarization, change with phase angle and wavelength. Such a modeling became possible due to development of a new version of MSTM (Multi Sphere T-Matrix) code for parallel computing. The results of the modeling are applied to the results of comet polarimetric observations to check if large aggregates dominate in formation of light scattering by comet dust. We compare aggregates of different structure and porosity. We show that large aggregates of more than 98% porosity (e.g. ballistic cluster-cluster aggregates) have angular dependence of polarization almost identical to the Rayleigh one. Large compact aggregates (less than 80% porosity) demonstrate the curves typical for solid particles. This rules out too porous and too compact aggregates as typical comet dust particles. We show that large aggregates not only can explain phase angle dependence of comet polarization in the near infrared but also may be responsible for the wavelength dependence of polarization, which can be related to their porosity.
We have used deep V and R images acquired at the ESO Very Large Telescope to identify the optical companion to the binary pulsar PSR J0610-2100, one of the black-widow millisecond pulsars recently detected by the Fermi Gamma-ray Telescope in the Galactic plane. We found a faint star (V~26.7) nearly coincident (\delta r ~0".28) with the pulsar nominal position. This star is visible only in half of the available images, while it disappears in the deepest ones (those acquired under the best seeing conditions), thus indicating that it is variable. Although our observations do not sample the entire orbital period (P=0.28 d) of the pulsar, we found that the optical modulation of the variable star nicely correlates with the pulsar orbital period and describes a well defined peak (R~25.6) at \Phi=0.75, suggesting a modulation due to the pulsar heating. We tentatively conclude that the companion to PSR J0610-2100 is a heavily ablated very low mass star (~ 0.02Msun) that completely filled its Roche Lobe.
Several lines of evidence, from isotopic analyses of meteorites to studies of the Sun's elemental and isotopic composition, indicate that the solar system was contaminated early in its evolution by ejecta from a nearby supernova (SN). Previous models have invoked SN material being injected into an extant protoplanetary disk, or isotropically expanding ejecta sweeping over a distant (>10 pc) cloud core, simultaneously enriching it and triggering its collapse. Here we consider a new astrophysical setting: the injection of clumpy SN ejecta, as observed in the Cas A SN remnant, into the molecular gas at the periphery of an HII region created by the SN's progenitor star. To track these interactions we have conducted a suite of high-resolution (1500^3 effective) 3D simulations that follow the evolution of individual clumps as they move into molecular gas. Even at these high resolutions, our simulations do not quite achieve numerical convergence, due to the challenge of properly resolving the small-scale mixing of ejecta and molecular gas, although they do allow some robust conclusions to be drawn. Isotropically exploding ejecta do not penetrate into the molecular cloud, but, if cooling is properly accounted for, clumpy ejecta penetrate to distances ~10^18 cm and mix effectively with star-forming molecular gas. The ~2 M_\odot high-metallicity ejecta from a core-collapse SN is likely to mix with ~2 \times 10^4 M_\odot of molecular gas. Thus all stars forming late (~5 Myr) in the evolution of an HII region may be contaminated by SN ejecta at a level ~10^-4. This level of contamination is consistent with the abundances of short-lived radionuclides and possibly some stable isotopic shifts in the early solar system, and is potentially consistent with the observed variability in stellar elemental abundances. SN contamination of forming planetary systems may be a common, universal process.
We present the results from a detailed analysis of photometric and spectrophotometric data on five Seyfert 1 galaxies observed as a part of a recent reverberation mapping program. The data were collected at several observatories over a 140-day span beginning in 2010 August and ending in 2011 January. We obtained high sampling-rate light curves for Mrk 335, Mrk 1501, 3C120, Mrk 6, and PG2130+099, from which we have measured the time lag between variations in the 5100 Angstrom continuum and the H-beta broad emission line. We then used these measurements to calculate the mass of the supermassive black hole at the center of each of these galaxies. Our new measurements substantially improve previous measurements of MBH and the size of the broad line-emitting region for four sources and add a measurement for one new object. Our new measurements are consistent with photoionization physics regulating the location of the broad line region in active galactic nuclei.
The horizon problem in the standard model of cosmology (LDCM) arises from the observed uniformity of the cosmic microwave background radiation, which has the same temperature everywhere (except for tiny, stochastic fluctuations), even in regions on opposite sides of the sky, which appear to lie outside of each other's causal horizon. Since no physical process propagating at or below lightspeed could have brought them into thermal equilibrium, it appears that the universe in its infancy required highly improbable initial conditions. In this paper, we examine this well-known problem by considering photon propagation through a Friedmann-Robertson-Walker (FRW) spacetime at a more fundamental level than has been attempted before, demonstrating that the horizon problem only emerges for a subset of FRW cosmologies, such as LCDM, that include an early phase of rapid deceleration. We show that the horizon problem is nonexistent for the recently introduced R_h=ct universe, obviating the principal motivation for the inclusion of inflation. We demonstrate through direct calculation that, in the R_h=ct universe, even opposite sides of the cosmos have remained causally connected to us - and to each other - from the very first moments in the universe's expansion. Therefore, within the context of the R_h=ct universe, the hypothesized inflationary epoch from t=10^{-35} seconds to 10^{-32} seconds was not needed to fix this particular "problem", though it may still provide benefits to cosmology for other reasons.
Ruprecht 147 is a hitherto unappreciated open cluster that holds great promise as a standard in fundamental stellar astrophysics. We have conducted a radial velocity survey of astrometric candidates with Lick, Palomar, and MMT observatories and have identified over 100 members, including 5 candidate blue stragglers, 11 red giants, and 5 SB2 binaries. We estimate the cluster metallicity from spectroscopic analysis, using Spectroscopy Made Easy (SME), and find it to be [M/H] = +0.08 \pm 0.03. We have obtained deep CFHT/MegaCam g'r'i'z' photometry and fit Padova isochrones to the (g' - i') and 2MASS (J - K) CMDs, using the \tau^2 maximum-likelihood procedure of Naylor (2009). We find best fits for isochrones at age t = 2.5 \pm 0.25 Gyr, m \pm M = 7.35 \pm 0.1, and A_V = 0.25 \pm 0.05, with significant uncertainty from the unresolved binary population and possibility of differential extinction across this large cluster. Our preferred model does not simultaneously fit the main sequence turnoff and the red giant branch in the optical CMD. We investigate alternative solutions and find that an older, closer and less extinguished Padova model with age t = 3.5 Gyr, m - M = 7.0, and A_V = 0.10 appears to better match the overall optical CMD (particularly the red giant branch). We do not favor this model because it poorly fits the upper main sequence in the optical, the age is inconsistent with our spectroscpic results, and our preferred model better fits the NIR CMD. Still, we cannot yet conclusively rule out the older solution. At 250 - 300 pc and an age of 2.5 - 3.5 Gyr, Ruprecht 147 is by far the oldest nearby star cluster.
Astronomical transients are intrinsically interesting things to study. Fast optical transients (microsecond timescale) are a largely unexplored field of optical astronomy mainly due to the fact that large optical telescopes are oversubscribed. Furthermore, most optical observations use instruments with integration times on the order of seconds and are thus unable to resolve fast transients. Current-generation atmospheric Cherenkov gamma-ray telescopes, however, have huge collecting areas (e.g., VERITAS, which consists of four 12-m telescopes), larger than any existing optical telescopes, and time is typically available for such studies without interfering with gamma-ray observations. The following outlines the benefits of using a Cherenkov telescope to detect optical transients and the implementation of the VERITAS Transient Detector (TRenDy), a dedicated multi-channel photometer based on field-programmable gate arrays. Data are presented demonstrating the ability of TRenDy to detect transient events such as a star passing through its field of view and the optical light curve of a pulsar.
It is an indisputable fact that solar magnetic fields are force-free in the corona, where force free fields means that current and magnetic fields are parallel and there is no Lorentz force in the fields. While the force-free extent of photospheric magnetic fields remains open. In this paper, the statistical results about it is given. The vector magnetograms (namely, $B_{x}$, $B_{y}$ and $B_{z}$ in heliocentric coordinates) are employed, which are deduced and calibrated from Stokes spectra, observed by Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS) are used. We study and calibrated 925 magnetograms calibrated by two sets of calibration coefficients, that indicate the relations between magnetic fields and the strength of Stokes spectrum and can be calculated either theoretically or empirically. The statistical results show that the majority of active region magnetic fields are not consistent with the force-free model.
The Square Kilometre Array and its pathfinders ASKAP and MeerKAT will produce
prodigious amounts of data that necessitate automated source finding. The
performance of automated source finders can be improved by pre-processing a
dataset. In preparation for the WALLABY and DINGO surveys, we have used a test
HI datacube constructed from actual Westerbork Telescope noise and WHISP HI
galaxies to test the real world improvement of linear smoothing, the {\sc
Duchamp} source finder's wavelet de-noising, iterative median smoothing and
mathematical morphology subtraction, on intensity threshold source finding of
spectral line datasets. To compare these pre-processing methods we have
generated completeness-reliability performance curves for each method and a
range of input parameters. We find that iterative median smoothing produces the
best source finding results for ASKAP HI spectral line observations, but
wavelet de-noising is a safer pre-processing technique.
In this paper we also present our implementations of iterative median
smoothing and mathematical morphology subtraction.
This papers explores the self similar solutions of the Vlasov-Poisson system and their relation to the gravitational collapse of dynamically cold systems. Analytic solutions are derived for power law potential in one dimension, and extensions of these solutions in three dimensions are proposed. Next the self similarity of the collapse of cold dynamical systems is investigated numerically. The fold system in phase space is consistent with analytic self similar solutions, the solutions present all the proper self-similar scalings. An additional point is the appearance of an $x^{-(1/2)}$ law at the center of the system for initial conditions with power law index larger than $-(1/2)$. It is found that the first appearance of the $x^{-(1/2)}$ law corresponds to the formation of a singularity very close to the center. Finally the general properties of self similar multi dimensional solutions near equilibrium are investigated. Smooth and continuous self similar solutions have power law behavior at equilibrium. However cold initial conditions result in discontinuous phase space solutions, and the smoothed phase space density looses its auto similar properties. This problem is easily solved by observing that the probability distribution of the phase space density $P$ is identical except for scaling parameters to the probability distribution of the smoothed phase space density $P_S$. As a consequence $P_S$ inherit the self similar properties of $P$. This particular property is at the origin of the universal power law observed in numerical simulation for ${\rho}/{\sigma^3}$. The self similar properties of $P_S$ implies that other quantities should have also an universal power law behavior with predictable exponents. This hypothesis is tested using a numerical model of the phase space density of cold dark matter halo's, an excellent agreement is obtained.
The background noise between 1 and 1.8 microns in ground-based instruments is
dominated by atmospheric emission from hydroxyl molecules. We have built and
commissioned a new instrument, GNOSIS, which suppresses 103 OH doublets between
1.47 - 1.7 microns by a factor of ~1000 with a resolving power of ~10,000. We
present the first results from the commissioning of GNOSIS using the IRIS2
spectrograph at the AAT. The combined throughput of the GNOSIS fore-optics,
grating unit and relay optics is ~36 per cent, but this could be improved to
~46 per cent with a more optimal design. We measure strong suppression of the
OH lines, confirming that OH suppression with fibre Bragg gratings will be a
powerful technology for low resolution spectroscopy. The integrated OH
suppressed background between 1.5 and 1.7 microns is reduced by a factor of 9
compared to a control spectrum using the same system without suppression. The
potential of low resolution OH suppressed spectroscopy is illustrated with
example observations.
The GNOSIS background is dominated by detector dark current below 1.67
microns and by thermal emission above 1.67 microns. After subtracting these we
detect an unidentified residual interline component of ~ 860 +/ 210
ph/s/m^2/micron/arcsec^2. This component is equally bright in the suppressed
and control spectra. We have investigated the possible source of the interline
component, but were unable to discriminate between a possible instrumental
artifact and intrinsic atmospheric emission. Resolving the source of this
emission is crucial for the design of fully optimised OH suppression
spectrographs. The next generation OH suppression spectrograph will be focussed
on resolving the source of the interline component, taking advantage of better
optimisation for a FBG feed. We quantify the necessary improvements for an
optimal OH suppressing fibre spectrograph design.
The interstellar medium (ISM) in galaxies is directly affected by the mass and energy outflows originating in regions of star formation. Magnetic fields are an essential ingredient of the ISM, but their connection to the gaseous medium and its evolution remains poorly understood. Here we present the detection of a gradient in Faraday rotation measure (RM), co-located with a hole in the neutral hydrogen (HI) distribution in the disk of the nearby spiral galaxy NGC 6946. The gas kinematics in the same location show evidence for infall of cold gas. The combined characteristics of this feature point to a substantial vertical displacement of the initially plane-parallel ordered magnetic field, driven by a localized star formation event. This reveals how the large-scale magnetic field pattern in galaxy disks is directly influenced by internal energetic phenomena. Conversely, magnetic fields are observed to be an important ingredient in disk-halo interactions, as predicted in MHD simulations. Turbulent magnetic fields at smaller spatial scales than the observed RM gradient will also be carried from the disk and provide a mechanism for the dynamo process to amplify the ordered magnetic field without quenching. We discuss the observational biases, and suggest that this is a common feature of star forming galaxies with active disk-halo flows.
XENON100 is a liquid xenon (LXe) time projection chamber built to search for rare collisions of hypothetical, weakly interacting massive particles (WIMPs). Operated in a low-background shield at the Gran Sasso underground laboratory in Italy, XENON100 has reached the unprecedented background level of $<$0.15 events/day/\kevr in the energy range below 100 \kevr in 30 kg of target mass, before electronic/nuclear recoil discrimination. It found no evidence for WIMPs during a dark matter run lasting for 100.9 live days in 2010, excluding with 90% confidence scalar WIMP-nucleon cross sections above 7x10$^{-45}$ cm$^{2}$ at a WIMP mass of 50 GeV/c$^{2}$. A new run started in March 2011, and more than 200 live days of WIMP-search data have been acquired. Results of this second run are expected to be released in summer 2012.
We show that suppression of the baryon energy gaps, caused by the relative motion of superfluid and normal liquid components, can substantially influence dynamical properties and evolution of neutron stars. This effect has been previously ignored in the neutron-star literature.
We propose a model in which there exists a real scalar field $q$ satisfying a condition $\dot{q} =MH$ and its energy density is given by $(1/2)\dot{q}^2+V(q)$, where $H$ is the Hubble parameter ($H=\dot{a}/a$) and $M$ is a mass scale characterizing the field. We show that the potential $V(q)$ of the field is uniquely determined by the condition. The potential depends on the energy densities of background matters. We find that the vacuum energy of the matters is cancelled by the potential of the field. As a result, the minimum of the total energy density of the matters and the field vanishes and is located at the infinite scale factor $a=\infty$. This remarkable property results without a supersymmetry. We show that the present tiny dark energy is caused by early inflation, while the energy is comparable to Planck scale before the inflation. As our model is reduced to the $\Lambda$CDM model in the limit $M\to 0$, it is a natural generalization of the $\Lambda$CDM model.
Context. The Australia Telescope Large Area Survey (ATLAS) aims to image a 7 deg2 region centred on the European Large Area ISO Survey - South 1 (ELAIS-S1) field and the Chandra Deep Field South (CDF-S) at 1.4 GHz with high sensitivity (up to ~10 \muJy) to study the evolution of star-forming galaxies (SFGs) and Active Galactic Nuclei (AGN) over a wide range of cosmic time. Aims. We present here ancillary radio observations at a frequency of 2.3 GHz obtained with the Australia Telescope Compact Array (ATCA). The main goal of this is to study the radio spectra of an unprecedented large sample of sources (~2000 observed, ~600 detected in both frequencies). Methods. With this paper, we provide 2.3 GHz source catalogues for both ATLAS fields, with a detection limit of 300 \muJy. We compute spectral indices between 1.4 GHz and 2.3 GHz using matched resolution images and investigate various properties of our source sample in dependence of their spectral indices. Results. We find the entire source sample to have a median spectral index of 0.74, in good agreement with both the canonical value of 0.7 for optically thin synchrotron radiation and other spectral index studies conducted by various groups. Regarding the radio spectral index as indicator for source type, we find only marginal correlations so that flat or inverted spectrum sources are usually powered by AGN and hence conclude that at least for the faint population the spectral index is not a strong discriminator. We investigate relation between spectral index and redshift for our source sample and find no such correlation at all. We do find a significant correlation between redshift and radio to near-infrared flux ratio, making this a much stronger tracer of high-z radio sources. We also find no evidence for a dependence of the radio-IR correlation on spectral index.
We present the XMM-Newton temperature profiles of 12 bright clusters of galaxies at 0.4<z<0.9, with 5<kT<11 keV. The normalized temperature profiles (normalized by the mean temperature T500) are found to be generally self-similar. The sample was subdivided in 5 cool-core (CC) and 7 non cool-core (NCC) clusters, by introducing a pseudo-entropy ratio sigma=(T_IN/T_OUT)X(EM_IN/EM_OUT)^-1/3 and defining the objects with sigma<0.6 as CC clusters and those with sigma>=0.6 as NCC clusters. The profiles of CC and NCC clusters differ mainly in the central regions, with the latters exhibiting a marginally flatter central profile. A significant dependence of the temperature profiles on the pseudo-entropy ratio sigma is detected by fitting a function of both r and sigma, showing an indication that the outer part of the profiles becomes steeper for higher values of sigma (i.e. transitioning towards the NCC clusters). No significant evidence of redshift evolution could be found within the redshift range sampled by our clusters (0.4<z<0.9). A comparison of our high-z sample with intermediate clusters at 0.1<z<0.3, showed how both the CC and NCC clusters temperature profiles have experienced some sort of evolution. This can be due by the fact that higher z clusters are at less advanced stage of their formation and did not have enough time to create a relaxed structure, characterized by a central temperature dip in CC clusters and by flatter profiles in NCC clusters. This is the first time that a systematic study of the temperature profiles of galaxy clusters at z>0.4 has been attempted, as we were able to define the closest possible relation to a Universal law for the temperature profiles of galaxy clusters at 0.1<z<0.9, showing a dependence on both the state of relaxation of the clusters and the redshift.
We investigate the instability of purely poloidal magnetic fields in nonrotating neutron stars by means of three-dimensional general-relativistic magnetohydrodynamics simulations, extending the work presented in Ciolfi et al. (2011). Our aim is to draw a clear picture of the dynamics associated with the instability and to study the final configuration reached by the system, thus obtaining indications on possible equilibria in a magnetized neutron star. Furthermore, since the internal rearrangement of magnetic fields is a highly dynamical process, which has been suggested to be behind magnetar giant flares, our simulations can provide a realistic estimate of the electromagnetic and gravitational-wave emission which should accompany the flare event. Our main findings are the following: (i) the initial development of the instability meets all the expectations of perturbative studies in terms of the location of the seed of the instability, the timescale for its growth and the generation of a toroidal component; (ii) in the subsequent nonlinear reorganization of the system, ~90% of magnetic energy is lost in few Alfven timescales mainly through electromagnetic emission, and further decreases on a much longer timescale; (iii) all stellar models tend to achieve a significant amount of magnetic helicity and the equipartition of energy between poloidal and toroidal magnetic fields, and evolve to a new configuration which does not show a subsequent instability on dynamical or Alfven timescales; (iv) the electromagnetic emission matches the duration of the initial burst in luminosity observed in giant flares, giving support to the internal rearrangement scenario; (v) only a small fraction of the energy released during the process is converted into f-mode oscillations and in the consequent gravitational-wave emission, thus resulting in very low chances of detecting this signal with present and..
G315.4-2.3 is a young Galactic supernova remnant (SNR), whose identification as the remains of a Type-II supernova (SN) explosion has been debated for a long time. In particular, recent multi-wavelength observations suggest that it is the result of a Type Ia SN, based on spectroscopy of the SNR shell and the lack of a compact stellar remnant.However, two X-ray sources, one detected by Einstein and ROSAT (Source V) and the other by Chandra (Source N) have been proposed as possible isolated neutron star candidates. In both cases, no clear optical identification was available and, therefore, we performed an optical and X-ray study to determine the nature of these two sources. Based on Chandra astrometry, Source V is associated with a bright V~14 star, which had been suggested based on the less accurate ROSAT position. Similarly, from VLT archival observations, we found that Source N is associated with a relatively bright star ($V=20.14 $). These likely identifications suggest that both X-ray sources cannot be isolated neutron stars.
The super-earth planet GJ 1214b has recently been the focus of several studies, using the transit spectroscopy technique, trying to determine the nature of its atmosphere. Here we focus on the Halpha line as a tool to further restrict the nature of GJ1214's atmosphere. We used the Gran Telescopio Canarias (GTC) OSIRIS instrument to acquire narrow band photometry with tunable filters. With our observations, we were able to observe the primary transit of the super-Earth GJ 1214b in three bandpasses: two centered in the continuum around Halpha (653.5 nm and 662.0 nm) and one centered at the line core (656.3 nm). We measure the depth of the planetary transit at each wavelength interval.By fitting analytic models to the measured light curves we were able to compute the depth of the transit at the three bandpasses. Taking the difference in the computed planet to star radius ratio between the line and the comparison continuum filters, we find Delta (Rp/Rstar)_{Halpha-653.5} = (6.60 +/- 3.54) 10^-3 and Delta (Rp/Rstar)_{Halpha-662.0} = (3.30 +/- 3.61) 10^-3. Although the planet radius is found to be larger in the Halpha line than in the surrounding continuum, the quality of our observations and the sigma level of the differences (1.8 and 1.0, respectively) does not allow us to claim an Halpha excess in GJ1214's atmosphere. Further observations will be needed to resolve this issue.
In order to put MIDI/VLTI observations of AGNs on a significant statistical basis, the number of objects had to be increased dramatically from the few prominent bright cases to over 20. For this, correlated fluxes as faint as ~ 150 mJy need to be observed, calibrated and their errors be estimated reliably. We have developed new data reduction methods for the coherent estimation of correlated fluxes with the Expert Work Station (EWS). They increase the signal/noise of the reduced correlated fluxes by decreasing the jitter in the group delay estimation. While correlation losses cannot be fully avoided for the weakest objects even with the improved routines, we have developed a method to simulate observations of weak targets and can now detect --- and correct for --- such losses. We have analyzed all sources of error that are relevant for the observations of weak targets. Apart from the photon-noise error, that is usually quoted, there is an additional error from the uncertainty in the calibration (i.e. the conversion factor). With the improved data reduction, calibration and error estimation, we can consistently and reproducibly observe fluxes as weak as ~ 150 mJy with an uncertainty of ~ 15 % under average conditions.
We briefly review the observations of the solar photosphere and pinpoint some open questions related to the magnetohydrodynamics of this layer of the Sun. We then discuss the current modelling efforts, addressing among other problems, that of the origin of supergranulation.
Collisionless relativistic shocks have been the focus of intense theoretical and numerical investigations and these interesting physics have a direct impact on the generation of energetic particles and the interpretation of gamma ray spectra. The Fermi acceleration process that takes place in these shocks is intimately linked with the excitation of micro-turbulence responsible for the shock formation, electron heating and supra-thermal tail generation that in turn excites micro-turbulence, developing thus a self-sustaining phenomenon. In this paper we discuss the development of the micro-turbulence and we investigate two important issues: firstly the transport of supra-thermal particles in the excited microturbulence upstream of the shock and its consequences for the efficiency of the Fermi process; secondly, the preheating process of the incoming background electrons as they cross the shock precursor and experience relativistic oscillations in the electric field of the micro-turbulence.We emphasize the importance of the motion of the electromagnetic disturbances relatively to the background plasma and to the shock front. The investigation is carried out for the two major instabilities involved in the precursor of relativistic shocks, the filamentation instability and the oblique two stream instability. Bearing in mind these new results, we analyze the performance of the Fermi acceleration process in various high energy sources and especially in the termination shock of gamma-ray bursts. We emphasize the high efficiency of a collisionless ultra-relativistic shock for accelerating electrons and radiating a synchrotron-like photon spectrum up to several GeV.
We present the implementation of an implicit-explicit (IMEX) Runge-Kutta numerical scheme for general relativistic hydrodynamics coupled to an optically thick radiation field in two existing GR-hydrodynamics codes. We argue that the necessity of such an improvement arises naturally in astrophysically relevant regimes where the optical thickness is high as the equations become stiff. By performing several 1D tests we verify the codes' new ability to deal with this stiffness and show consistency. Then, still in 1D, we compute a luminosity versus accretion rate diagram for the setup of spherical accretion onto a Schwarzschild black hole and find good agreement with previous work. Lastly, we revisit the supersonic Bondi Hoyle Lyttleton (BHL) accretion in 2D where we can now present simulations of realistic temperatures, down to T~10^6 K. Here we find that radiation pressure plays an important role, but also that these highly dynamical set-ups push our approximate treatment towards the limit of physical applicability. The main features of radiation hydrodynamics BHL flows manifest as (i) an effective adiabatic index approaching gamma_effective ~ 4/3; (ii) accretion rates two orders of magnitude lower than without radiation pressure; (iii) luminosity estimates around the Eddington limit, hence with an overall radiative efficiency as small as eta ~ 10^{-2}; (iv) strong departures from thermal equilibrium in shocked regions; (v) no appearance of the flip-flop instability. We conclude that the current optically thick approximation to the radiation transfer does give physically substantial improvements over the pure hydro also in set-ups departing from equilibrium, and, once accompanied by an optically thin treatment, is likely to provide a fundamental tool for investigating accretion flows in a large variety of astrophysical systems.
We present compelling evidence for the complexity of the Fornax dwarf spheroidal. By disentangling three different stellar subpopulations in its red giant branch, we are able to study in detail the dependence between kinematics and metallicity. A well-defined ordering in velocity dispersion, spatial concentration, and metallicity is evident in the subpopulations. We also present evidence for a significant misalignment between the angular momentum vectors of the old and intermediate-age populations. According to the HST measurement of Fornax's proper motion, this corresponds to counter-rotation. These ingredients are used to construct a novel evolutionary history of the Fornax dwarf spheroidal, characterized as a late merger of a bound pair.
Photometric calibration is currently the dominant source of systematic uncertainty in exploiting type Ia supernovae to determine the nature of the dark energy. We review our ongoing program to address this calibration challenge by performing measurements of both the instrumental response function and the optical transmission function of the atmosphere. A key aspect of this approach is to complement standard star observations by using NIST-calibrated photodiodes as a metrology foundation for optical flux measurements. We present our first attempt to assess photometric consistency between synthetic photometry and observations, by comparing predictions based on a NIST-diode-based determination of the PanSTARRS-1 instrumental response and empirical atmospheric transmission measurements, with fluxes we obtained from observing spectrophotometric standards.
Gamma ray burst (GRBs) can be used to constrain cosmological parameters from medium up to very high redshift. These powerful systems could be the further reliable distance indicators after SNeIa supernovae. We consider GRBs samples to achieve the luminosity distance to redshift relation and derive the values of the cosmographic parameters considering several possible scaling relations. GRBs, if calibrated by SNeIa, seem reliable as distance indicators and give cosmographic parameters in good agreement with the LCDM model. GRBs correlations with neutrino and gravitational wave signals are also investigated in view of high energy neutrino experiments and gravitational wave detectors as LIGO-VIRGO. A discussion on the GRB afterglow curve up to the visible and radio wavelengths is developed considering the possibility to use the Square Kilometer Array (SKA) telescope to achieve the first GRB-radio survey.
We present a new observational campaign, DWARF, aimed at detection of circumbinary extrasolar planets using the timing of the minima of low-mass eclipsing binaries. The observations will be performed within an extensive network of relatively small to medium-size telescopes with apertures of ~20-200 cm. The starting sample of the objects to be monitored contains (i) low-mass eclipsing binaries with M and K components, (ii) short-period binaries with sdB or sdO component, and (iii) post-common-envelope systems containing a WD, which enable to determine minima with high precision. Since the amplitude of the timing signal increases with the orbital period of an invisible third component, the timescale of project is long, at least 5-10 years. The paper gives simple formulas to estimate suitability of individual eclipsing binaries for the circumbinary planet detection. Intrinsic variability of the binaries (photospheric spots, flares, pulsation etc.) limiting the accuracy of the minima timing is also discussed. The manuscript also describes the best observing strategy and methods to detect cyclic timing variability in the minima times indicating presence of circumbinary planets. First test observation of the selected targets are presented.
A reviewed calculation of lepton spectra produced in cosmic ray induced extensive air showers is carried out with a primary cosmic ray spectrum that fits the latest direct measurements below the knee. In order to achieve this, we used a full Monte Carlo method to derive the inclusive differential spectra (yields) of muons, muon neutrinos and electron neutrinos at the surface for energies between 80 GeV and hundreds of PeV. The air shower simulator CORSIKA 6.990 was used for showering and propagation of the secondary particles through the atmosphere, employing the established high energy hadronic interaction models SIBYLL 2.1, QGSJet-01 and QGSJet-II-03. We show that the performance of the interaction models allows makes it possible to predict the spectra within experimental uncertainties, while SIBYLL generally yields a higher flux at the surface than the QGSJet models. The calculation of the flavor and charge ratios has lead to inconsistent results, mainly influenced by the different representations of the K/$\pi$ ratio within the models. The influence of the knee of cosmic rays is reflected in the secondary spectra at energies between 100 and 200 TeV. Furthermore, we could quantify systematic uncertainties of atmospheric muon- and neutrino fluxes, associated to the models of the primary cosmic ray spectrum and the interaction models. For most recent parametrizations of the cosmic ray primary spectrum, atmospheric muons can be determined with an uncertainty smaller than $^{+15}_{-13}$% of the average flux. Uncertainties of the muon- and electron neutrino fluxes can be calculated within an average error of $^{+32}_{-22}$% and $^{+25}_{-19}$%, respectively.
At very high energies (VHE), the gamma-ray horizon of the universe is limited to redshifts z<<1, and, therefore, any observation of TeV radiation from a source located beyond z=1 would require a dramatic revision of the standard scenarios of propagation of VHE photons through intergalactic radiation and magnetic fields. This appears to be the case for the TeV blazar PKS 0447-439, for which a redshift z>1.246 was recently reported. In this paper we argue that the reported large redshift can be compatible with gamma-ray emission extending to TeV energies, without invoking exotic new physics, if one assumes that the observed gamma rays are secondary photons produced in interactions of high-energy protons originating from the blazar jet and propagating over the cosmological distances almost rectilinearly. This hypothesis was initially proposed as a possible explanation for the TeV gamma rays observed from blazars with relatively large, yet modest redshifts, z~0.2, for which other explanations were possible. In the case of PKS 0447-439, it provides the only viable interpretation of the VHE signal consistent with conventional physics. If the observability of TeV gamma rays from blazars at z>1 is confirmed by future observations, our interpretation will have far-reaching ramifications for gamma-ray astronomy. Furthermore, this interpretation implies that intergalactic magnetic fields (IGMFs) along the line of sight are very weak, in the range 0.01 fG < B < 1 fG. and that acceleration of E> 0.1 EeV protons in the AGN jets is indeed very efficient.
We present measurements of the angular diameter distance D_A(z) and the Hubble parameter H(z) at z=0.35 using the anisotropy of the baryon acoustic oscillation (BAO) signal measured in the galaxy clustering distribution of the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) Luminous Red Galaxies (LRG) sample. Our work is the first to apply density-field reconstruction to an anisotropic analysis of the acoustic peak. Reconstruction partially removes the effects of non-linear evolution and redshift-space distortions in order to sharpen the acoustic signal. We present the theoretical framework behind the anisotropic BAO signal and give a detailed account of the fitting model we use to extract this signal from the data. Our method focuses only on the acoustic peak anisotropy, rather than the more model-dependent anisotropic information from the broadband power. We test the robustness of our analysis methods on 160 LasDamas DR7 mock catalogues and find that our models are unbiased at the ~0.2% level in measuring the BAO anisotropy. After reconstruction we measure D_A(z=0.35)=1050+/-38 Mpc and H(z=0.35)=84.4+/-7.1 km/s/Mpc assuming a sound horizon of r_s=152.76 Mpc. Note that these measurements are correlated with a correlation coefficient of 0.58. This represents a factor of 1.4 improvement in the error on D_A relative to the pre-reconstruction case; a factor of 1.3 improvement is seen for H.
The first station of the Long Wavelength Array (LWA1) was completed in April 2011 and is currently performing observations resulting from its first call for proposals in addition to a continuing program of commissioning and characterization observations. The instrument consists of 258 dual-polarization dipoles, which are digitized and combined into beams. Four independently-steerable dual-polarization beams are available, each with two "tunings" of 16 MHz bandwidth that can be independently tuned to any frequency between 10 MHz and 88 MHz. The system equivalent flux density for zenith pointing is ~3 kJy and is approximately independent of frequency; this corresponds to a sensitivity of ~5 Jy/beam (5sigma, 1 s); making it one of the most sensitive meter-wavelength radio telescopes. LWA1 also has two "transient buffer" modes which allow coherent recording from all dipoles simultaneously, providing instantaneous all-sky field of view. LWA1 provides versatile and unique new capabilities for Galactic science, pulsar science, solar and planetary science, space weather, cosmology, and searches for astrophysical transients. Results from LWA1 will detect or tightly constrain the presence of hot Jupiters within 50 parsecs of Earth. LWA1 will provide excellent resolution in frequency and in time to examine phenomena such as solar bursts, and pulsars over a 4:1 frequency range that includes the poorly understood turnover and steep-spectrum regimes. Observations to date have proven LWA1's potential for pulsar observing, and just a few seconds with the completed 256-dipole LWA1 provide the most sensitive images of the sky at 23 MHz obtained yet. We are operating LWA1 as an open skies radio observatory, offering ~2000 beam-hours per year to the general community.
Massive binary stars may constitute a substantial fraction of progenitors to supernovae and gamma-ray bursts, and the distribution of their orbital characteristics holds clues to the formation process of massive stars. As a contribution to securing statistics on OB-type binaries, we report the discovery and orbital parameters for five new systems as part of the Cygnus OB2 Radial Velocity Survey. Four of the new systems (MT070, MT174, MT267, and MT734 (a.k.a. VI Cygni #11) are single-lined spectroscopic binaries while one (MT103) is a double-lined system (B1V+B2V). MT070 is noteworthy as the longest period system yet measured in Cyg OB2, with P=6.2 yr. The other four systems have periods ranging between 4 and 73 days. MT174 is noteworthy for having a probable mass ratio q<0.1, making it a candidate progenitor to a low-mass X-ray binary. These measurements bring the total number of massive binaries in Cyg OB2 to 25, the most currently known in any single cluster or association.
The results of a spectroscopic survey of epsilon Aurigae during eclipse using a network of small telescopes are presented. The spectra have a resolution of 0.35 to 0.65{\AA} and cover the period 2008 to 2012 with a typical interval of 4 days during eclipse. This paper specifically covers variations in the K I 7699{\AA}, Na D and Mg II 4481{\AA} lines. Absorption started increasing in the KI 7699{\AA} line 3 months before the eclipse began photometrically and had not returned to pre eclipse levels by the end of the survey March 2012, 7 months after the brightness had returned to normal outside eclipse levels. The contribution of the eclipsing object to the KI 7699{\AA} line has been isolated and the data show the excess absorption increasing and decreasing in a series of steps during ingress and egress. This is interpreted as an indication of structure within the eclipsing object. The F star is totally obscured by the eclipsing object at the Na D wavelength during eclipse. The radial velocity of the F star and the mean and maximum radial velocity of the eclipsing material in front of the F star at any given time have been isolated and tracked throughout the eclipse. The quasi-periodic variations seen in the F star RV outside eclipse continued during the eclipse. It is hoped that these results can be used to constrain proposed models of the system and its components.
Two methods are developed for solving the steady-state spherically symmetric radiative transfer equation for resonance line radiation emitted by a point source in the Intergalactic Medium. One method is based on solving the ray and moment equations using finite differences. The second uses a Monte Carlo approach incorporating methods that greatly improve the accuracy compared with previous approaches in this context. Several applications are presented serving as test problems for both a static medium and an expanding medium, including inhomogeneities in the density and velocity fields. Solutions are obtained in the coherent scattering limit and for Doppler RII redistribution with and without recoils. We find generally that the radiation intensity is linear in the cosine of the azimuthal angle with respect to radius to high accuracy over a broad frequency region across the line centre for both linear and perturbed velocity fields, yielding the Eddington factors f(nu) = 1/3 and g(nu) = 3/5. We show the radiation field produced by a point source divides into three spatial regimes for a uniformly expanding homogeneous medium: at radii r small compared with a characteristic radius r*, the mean intensity near line centre varies as 1/ r^(7/3), while at r > r* it approaches 1/ r^2; for r << r* it is modified by frequency redistribution. Before the reionization epoch, r* takes on the universal value 1.1 Mpc, independent of redshift. The mean intensity and scattering rate are found to be very sensitive to the gradient of the velocity field, growing exponentially with the amplitude of the perturbation as the limit of a vanishing velocity gradient is approached near the source. We expect the 21cm signal from the Epoch of Reionization to thus be a sensitive probe of both the density and the peculiar velocity fields.
We present a power spectral density analysis of the 1-minute cadence Kepler light-curve data of the cataclysmic variable V1504 Cygni. We identify three distinct periods: orbital period, the superhump period, and the infrahump period. The results are consistent with those predicted by the period excess-deficit relation.
The Swift-XRT observations of the early X-ray afterglow of GRBs show that it usually begins with a steep decay phase. A possible origin of this early steep decay is the high latitude emission that subsists when the on-axis emission of the last dissipating regions in the relativistic outflow has been switched-off. We wish to establish which of various models of the prompt emission are compatible with this interpretation. We successively consider internal shocks, photospheric emission, and magnetic reconnection and obtain the typical decay timescale at the end of the prompt phase in each case. Only internal shocks naturally predict a decay timescale comparable to the burst duration, as required to explain XRT observations in terms of high latitude emission. The decay timescale of the high latitude emission is much too short in photospheric models and the observed decay must then correspond to an effective and generic behavior of the central engine. Reconnection models require some ad hoc assumptions to agree with the data, which will have to be validated when a better description of the reconnection process becomes available.
We present a spectroscopic study of the incidence of AGN nuclear activity in two samples of isolated galaxies (Karachentseva, V.E. & Varela, J.). Our results show that the incidence of non-thermal nuclear activity is about 43% and 31% for galaxies with emission lines and for the total sample 40% and 27% respectively. For the first time we have a large number of bona-fide isolated galaxies (513 objects), with statistically significant number of all types. We find a clear relation between bulge mass and the incidence of nuclear activity in the sample with emission lines. This relation becomes flatter when we take into account the complete sample with no emission line galaxies. A large fration ($\sim$70%) of elliptical galaxies or early type spirals have an active galactic nucleus and $\sim$70% of them are LINERs. Only 3% of the AGN show the presence of broad lines (a not a single one can be classified as type 1 AGN). This is a remarkable result which is completely at odds with the unified model even if we consider warped or clumpy tori. Finally, we interpretation the large fration of AGN in isolated galaxies as the result of secular evolution of their supermasive black holes.
The origin and structure of the magnetic fields in the interstellar medium of spiral galaxies is investigated with 3D, non-ideal, compressible MHD simulations, including stratification in the galactic gravity field, differential rotation and radiative cooling. A rectangular domain, 1x1x2 kpc^{3} in size, spans both sides of the galactic mid-plane. Supernova explosions drive transonic turbulence. A seed magnetic field grows exponentially to reach a statistically steady state within 1.6 Gyr. Following Germano (1992) we use volume averaging with a Gaussian kernel to separate magnetic field into a mean field and fluctuations. Such averaging does not satisfy all Reynolds rules, yet allows a formulation of mean-field theory. The mean field thus obtained varies in both space and time. Growth rates differ for the mean-field and fluctuating field and there is clear scale separation between the two elements, whose integral scales are about 0.7 kpc and 0.3 kpc, respectively.
In U. Nucamendi et al. Phys. Rev. D63 (2001) 125016 and K. Lake, Phys. Rev. Lett. 92 (2004) 051101 it has been shown that galactic potentials can be kinematically linked to the observed red/blue shifts of the corresponding galactic rotation curves under a minimal set of assumptions: the emitted photons come from stable timelike circular geodesic orbits of stars in a static spherically symmetric gravitational field, and propagate to us along null geodesics. It is remarkable that this relation can be established without appealing at all to a concrete theory of gravitational interaction. Here we generalize this kinematical spherically symmetric approach to the galactic rotation curves problem to the stationary axisymmetric realm since this is precisely the symmetry that spiral galaxies possess. Thus, by making use of the most general stationary axisymmetric metric, we also consider stable circular orbits of stars that emit signals which travel to a distant observer along null geodesics and express the galactic red/blue shifts in terms of three arbitrary metric functions, clarifying the contribution of the rotation as well as the dragging of the gravitational field. This stationary axisymmetric approach distinguishes between red and blue shifts emitted by circularly orbiting receding and approaching stars, respectively, even when they are considered with respect to the center of a spiral galaxy, indicating the need of precise measurements in order to confront predictions with observations. We also point out the difficulties one encounters in the attempt of determining the metric functions from observations and list some possible strategies to overcome them.
Variable NaI absorption lines have been reported in a number of type Ia supernovae (SNeIa). The presence of this circumstellar material suggests that cataclysmic variables (CVs) with a giant donor star may be the progenitors of these SNeIa (Patat et al. 2007). We present echelle spectra of the CV QU Carinae which strengthen the connection between CVs of the V Sge class, the Accretion Wind Evolution scenario, variable wind features, variable NaI absorption, and SNIa. This thread not only provides insight into the spectral peculiarities of QU Car, but also links SNeIa as a class with their parent systems.
It is now well established that Kepler's supernova remnant is the result of a Type Ia explosion. With an age of 407 years, and an angular diameter of ~ 4', Kepler is estimated to be between 3.0 and 7.0 kpc distant. Unlike other Galactic Type Ia supernova remnants such as Tycho and SN 1006, and SNR 0509-67.5 in the Large Magellanic Cloud, Kepler shows evidence for a strong circumstellar interaction. A bowshock structure in the north is thought to originate from the motion of a mass-losing system through the interstellar medium prior to the supernova. We present results of hydrodynamical and spectral modeling aimed at constraining the circumstellar environment of the system and the amount of 56Ni produced in the explosion. Using models that contain either 0.3 M_sun (subenergetic) or 1 M_sun (energetic) of 56Ni, we simulate the interaction between supernova Ia ejecta and various circumstellar density models. Based on dynamical considerations alone, we find that the subenergetic models favor a distance to the SNR of < 6.4 kpc, while the model that produces 1 M_sun of 56Ni requires a distance to the SNR of > 7 kpc. The X-ray spectrum is consistent with an explosion that produced ~ 1 M_sun of 56Ni, ruling out the subenergetic models, and suggesting that Kepler's SNR was a SN 1991T-like event. Additionally, the X-ray spectrum rules out a pure 1/r^2 wind profile expected from isotropic mass loss up to the time of the supernova. Introducing a small cavity around the progenitor system results in modeled X-ray spectra that are consistent with the observed spectrum. If a wind shaped circumstellar environment is necessary to explain the dynamics and X-ray emission from the shocked ejecta in Kepler's SNR, then we require that the distance to the remnant be greater than 7 kpc.
We discuss the potential of the eROSITA telescope on board the \emph{Spectrum-X-Gamma} observatory to detect gamma-ray burst (GRB) X-ray afterglows during its 4-year all-sky survey. The expected rate of afterglows associated with long-duration GRBs without any information on the bursts proper that can be identified by a characteristic power-law light curve in the eROSITA data is 4--8 events per year. An additional small number, $\lesssim 2$ per year, of afterglows may be associated with short GRBs, ultra hard (GeV) GRBs and X-ray flashes. eROSITA can thus provide the first unbiased (unaffected by GRB triggering) sample of $\lesssim 40$ X-ray afterglows, which can be used for statistical studies of GRB afterglows and for constraining the shape of the GRB $\log N$--$\log S$ distribution at its low-fluence end. The total number of afterglows detected by eROSITA may be yet higher due to orphan afterglows and failed GRBs. The actual detection rate could thus provide interesting constraints on the properties of relativistic jets associated with collapse of massive stars. Finally, eROSITA can provide accurate ($\lesssim 30"$) coordinates of newly discovered afterglows within a day after the event, early enough for scheduling further follow-up observations.
We have performed detailed calculations of spectra and light curves of GRB afterglows assuming that the observed GRBs can have a jet geometry. The calculations are based on an expanding relativistic shock GRB afterglow model where the afterglow is the result of synchrotron radiation of relativistic electrons with power-law energy distribution at the front of external shock being decelerated in a circumstellar medium. To determine the intensity on the radiation surface we solve numerically the full time-, angle-, and frequency-dependent special relativistic transfer equation in the comoving frame using the method of long characteristics.
Weakly Interacting Massive Particles (WIMPs) may constitute most of the
matter in the Universe. While there are intriguing results from DAMA/LIBRA,
CoGeNT and CRESST-II, there is not yet a compelling detection of dark matter.
The ability to detect the directionality of recoil nuclei will considerably
facilitate detection of WIMPs by means of "annual modulation effect" and
"diurnal modulation effect". Directional sensitivity requires either extremely
large gas (TPC) detectors or detectors with a few nanometer spatial resolution.
In this paper we propose a novel type of dark matter detector: detectors made
of DNA could provide nanometer resolution for tracking, an energy threshold of
0.5 keV, and can operate at room temperature. When a WIMP from the Galactic
Halo elastically scatters off of a nucleus in the detector, the recoiling
nucleus then traverses thousands of strings of single stranded DNA (ssDNA) (all
with known base sequences) and severs those ssDNA strands it hits. The location
of the break can be identified by amplifying and identifying the segments of
cut ssDNA using techniques well known to biologists. Thus the path of the
recoiling nucleus can be tracked to nanometer accuracy. In one such detector
concept, the transducers are a few nanometer-thick Au-foils of 1m times1m, and
the direction of recoiling nuclei is measured by "DNA Tracking Chamber"
consisting of ordered array of ssDNA strands. Polymerase Chain Reaction (PCR)
and ssDNA sequencing are used to read-out the detector. The detector consists
of roughly 1 kg of gold and 0.1 kg of DNA packed into (1m)^3. By leveraging
advances in molecular biology, we aim to achieve about 1,000-fold better
spatial resolution than in conventional WIMP detectors at reasonable cost.
Physical cosmology tries to understand the Universe at large with its origin and evolution. Observational and experimental situations in cosmology do not allow us to proceed purely based on the empirical means. We examine in which sense our cosmological assumptions in fact have shaped our current cosmological worldview with consequent inevitable limits. Cosmology, as other branches of science and knowledge, is a construct of human imagination reflecting the popular belief system of the era. The question at issue deserves further philosophic discussions. In Whitehead's words, "philosophy, in one of its functions, is the critic of cosmologies". (Whitehead 1925)
Kinetic plasma theory is used to generate synthetic spacecraft data to analyze and interpret the compressible fluctuations in the inertial range of solar wind turbulence. The kinetic counterparts of the three familiar linear MHD wave modes---the fast, Alfven, and slow waves---are identified and the properties of the density-parallel magnetic field correlation for these kinetic wave modes is presented. The construction of synthetic spacecraft data, based on the quasi-linear premise---that some characteristics of magnetized plasma turbulence can be usefully modeled as a collection of randomly phased, linear wave modes---is described in detail. Theoretical predictions of the density-parallel magnetic field correlation based on MHD and Vlasov-Maxwell linear eigenfunctions are presented and compared to the observational determination of this correlation based on 10 years of Wind spacecraft data. It is demonstrated that MHD theory is inadequate to describe the compressible turbulent fluctuations and that the observed density-parallel magnetic field correlation is consistent with a statistically negligible kinetic fast wave energy contribution for the large sample used in this study. A model of the solar wind inertial range fluctuations is proposed comprised of a mixture of a critically balanced distribution of incompressible Alfvenic fluctuations and a critically balanced or more anisotropic than critical balance distribution of compressible slow wave fluctuations. These results imply that there is little or no transfer of large scale turbulent energy through the inertial range down to whistler waves at small scales.
Since the Standard Model most probably cannot explain the large value of CP asymmetries recently observed in D-meson decays we propose the fourth quark-lepton generation explanation of it. As a byproduct weakly mixed leptons of the fourth generation make it possible to save the baryon number of the Universe from erasure by sphalerons. An impact of the 4th generation on BBN is briefly discussed.
We linearize the field equations for higher order theories of gravity that contain scalar invariants other than the Ricci scalar. We find that besides a massless spin-2 field (the standard graviton), the theory contains also spin-0 and spin-2 massive modes with the latter being, in general, ghost modes. The rate at which such particles would emit gravitational Cherenkov radiation is calculated for some interesting physical cases.
One of the main motivations behind formulating the general theory of relativity was to provide a mathematical description to the Mach's principle. However, soon after its formulation, it was realized that the theory does not follow Mach's principle. As the theoretical predictions were matching with the observations, Einstein believed that the theory was correct and did not make any farther attempt to reformulate the theory to explain Mach's principle. Later on, several attempts were made by different researchers to formulate the theory of gravity based on Mach's principle. However most of these theories remain unsuccessful to explain different physical phenomena. In this report I have proposed a new theory of gravity which is completely based on the Mach's principle. The theory can explain the galactic velocity profiles up to a high degree of accuracy, without demanding the existence of any dark matter component in the universe. The theory can also explain the accelerated expansion of the universe without Dark Energy. It is a metric theory and can be derived from the action principle, which guarantees energy or momentum conservation. Modern theories like TeVeS or Modified gravity give some mathematical modification of the Einstein's equation to explain different observational phenomenon like the galactic velocity profile, accelerated expansion of the universe or CMBR power spectrum. Most of these theories don't have any underlying logic. However, the new theory explained in this paper, is a mathematical formulation of the Mach's principle. Therefore, the theory is not just a mathematical jugglery to explain some observed facts, but arises from a deep physical argument.
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