- ID:
- ivo://CDS.VizieR/J/A+A/549/A102
- Title:
- White dwarf cooling sequences
- Short Name:
- J/A+A/549/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new diagnostics of white dwarf (WD) cooling sequences and luminosity functions (LFs) in the near-infrared (NIR) bands that will exploit the sensitivity and resolution of future extremely large telescopes. The collision-induced absorption (CIA) of molecular hydrogen causes a clearly defined blue turn-off along the WD (WDBTO) cooling sequences and a bright secondary maximum in the WD LFs. These features are independent of age over a broad age range and are minimally affected by metal abundance. This means that the NIR magnitudes of the WDBTO are very promising distance indicators.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/555/A96
- Title:
- White dwarf cooling timescales
- Short Name:
- J/A+A/555/A96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An accurate assessment of white dwarf cooling times is paramount so that white dwarf cosmochronology of Galactic populations can be put on more solid grounds. This issue is particularly relevant in view of the enhanced observational capabilities provided by the next generation of extremely large telescopes, that will offer more avenues to use white dwarfs as probes of Galactic evolution and test-beds of fundamental physics. We estimate for the first time the consistency of results obtained from independent evolutionary codes for white dwarf models with fixed mass and chemical stratification, when the same input physics is employed in the calculations. We compute and compare cooling times obtained from two independent and widely used stellar evolution codes, BaSTI and LPCODE evolutionary codes, using exactly the same input physics for 0.55M_{sun}_ white dwarf models with both pure carbon and uniform carbon-oxygen (50/50 mass fractions) cores , and pure hydrogen layers with mass fraction qH=10^-4^M_WD_ on top of pure helium buffers of mass qHe=10^-2^M_WD_.
- ID:
- ivo://CDS.VizieR/J/MNRAS/412/1162
- Title:
- Wind-driving protostellar accretion discs
- Short Name:
- J/MNRAS/412/1162
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We continue our study of weakly ionized protostellar accretion discs that are threaded by a large-scale magnetic field and power a centrifugally driven wind. It has been argued that there is already evidence in several protostellar systems that such a wind transports a significant fraction of the angular momentum from at least some part of the disc. We model this situation by considering a radially localized disc model in which the matter is everywhere well coupled to the field and the wind is the main repository of excess angular momentum. We consider stationary configurations in which magnetic diffusivity counters the shearing and advection of the magnetic field lines. In Wardle & Koenigl (1997, ASP Conf. Ser., 121, 561) we analysed the disc structure in the hydrostatic approximation (vertical motions neglected inside the disc) and presented exact disc/wind solutions for the ambipolar diffusivity regime. In Koenigl, Salmeron & Wardle (Paper I, 2010MNRAS.401..479K) we generalized the hydrostatic analysis to the Hall and Ohm diffusivity domains and used it to identify the disc parameter sub-regimes in which viable solutions with distinct physical properties can be expected to occur. In this paper we test the results of Paper I by deriving full numerical solutions (integrated through the sonic critical surface) of the disc equations in the Hall domain.
- ID:
- ivo://CDS.VizieR/J/A+A/564/A84
- Title:
- WISE model grids for O- and C-rich AGB
- Short Name:
- J/A+A/564/A84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Since asymptotic giant branch (AGB) stars are bright and extended infrared objects, most Galactic AGB stars saturate the Wide-field Infrared Survey Explorer (WISE) detectors and therefore the WISE magnitudes that are restored by applying point-spread-function fitting need to be verified. Statistical properties of circumstellar envelopes around AGB stars are discussed on the basis of a WISE AGB catalog verified in this way. We cross-matched an AGB star sample with the WISE All-Sky Source Catalog and the Two Mircon All Sky Survey catalog. Infrared Space Observatory (ISO) spectra of a subsample of WISE AGB stars were also exploited. The dust radiation transfer code DUSTY was used to help predict the magnitudes in the W1 and W2 bands, the two WISE bands most affected by saturation, for calibration purpose, and to provide physical parameters of the AGB sample stars for analysis.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/41
- Title:
- X-ray binary evolution across cosmic time
- Short Name:
- J/ApJ/764/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-redshift galaxies permit the study of the formation and evolution of X-ray binary (XRB) populations on cosmological timescales, probing a wide range of metallicities and star formation rates (SFRs). In this paper, we present results from a large-scale population synthesis study that models the XRB populations from the first galaxies of the universe until today. We use as input to our modeling the Millennium II cosmological simulation (Boylan-Kolchin et al. 2009MNRAS.398.1150B) and the updated semi-analytic galaxy catalog by Guo et al. (2011MNRAS.413..101G) to self-consistently account for the star formation history and metallicity evolution of the universe. Our modeling, which is constrained by the observed X-ray properties of local galaxies, gives predictions about the global scaling of emission from XRB populations with properties such as SFR and stellar mass, and the evolution of these relations with redshift. Our simulations show that the X-ray luminosity density (X-ray luminosity per unit volume) from XRBs in our universe today is dominated by low-mass XRBs, and it is only at z>~2.5 that high-mass XRBs become dominant. We also find that there is a delay of ~1.1Gyr between the peak of X-ray emissivity from low-mass XRBs (at z~2.1) and the peak of SFR density (at z~3.1). The peak of the X-ray luminosity from high-mass XRBs (at z~3.9) happens ~0.8Gyr before the peak of the SFR density, which is due to the metallicity evolution of the universe.
- ID:
- ivo://CDS.VizieR/J/A+A/545/A120
- Title:
- X-ray bursting neutron star atmos. models. II
- Short Name:
- J/A+A/545/A120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Theoretical spectra of X-ray bursting neutron star (NS) model atmospheres are widely used for determination of the NS basic parameters such as their masses and radii. Compton scattering, that plays an important role in spectra formation at high luminosities, is often accounted for using the differential Kompaneets operator, while in other models a more general, integral operator for the Compton scattering kernel is used. We construct here accurate NS atmosphere models using exact treatment of Compton scattering with the integral relativistic kinetic equation and exact relativistic angle-dependent redistribution function.
- ID:
- ivo://CDS.VizieR/J/A+A/527/A139
- Title:
- X-ray bursting neutron star atmosphere models
- Short Name:
- J/A+A/527/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray bursting neutron stars in low mass X-ray binaries constitute an appropriate source class to constrain masses and radii of neutron stars, but a sufficiently extended set of corresponding model atmospheres is necessary for these investigations. Methods. We computed such a set of model atmospheres and emergent spectra in a plane-parallel, hydrostatic, and LTE approximation with Compton scattering taken into account.
- ID:
- ivo://CDS.VizieR/J/ApJ/774/136
- Title:
- X-ray obs. of SINGS gal. compared to models
- Short Name:
- J/ApJ/774/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the largest-scale comparison to date between observed extragalactic X-ray binary (XRB) populations and theoretical models of their production. We construct observational X-ray luminosity functions (oXLFs) using Chandra observations of 12 late-type galaxies from the Spitzer Infrared Nearby Galaxy Survey. For each galaxy, we obtain theoretical XLFs (tXLFs) by combining XRB synthetic models, constructed with the population synthesis code StarTrack, with observational star formation histories (SFHs). We identify highest-likelihood models both for individual galaxies and globally, averaged over the full galaxy sample. Individual tXLFs successfully reproduce about half of the oXLFs, but for some galaxies we are unable to find underlying source populations, indicating that galaxy SFHs and metallicities are not well matched and/or that XRB modeling requires calibration on larger observational samples. Given these limitations, we find that the best models are consistent with a product of common envelope ejection efficiency and central donor concentration =~0.1, and a 50% uniform-50% "twins" initial mass-ratio distribution. We present and discuss constituent subpopulations of tXLFs according to donor, accretor, and stellar population characteristics. The galaxy-wide X-ray luminosity due to low-mass and high-mass XRBs, estimated via our best global model tXLF, follows the general trend expected from the L_X_-star formation rate and L_X_-stellar mass relations of Lehmer et al. Our best models are also in agreement with modeling of the evolution of both XRBs over cosmic time and of the galaxy X-ray luminosity with redshift.
- ID:
- ivo://CDS.VizieR/J/ApJ/880/29
- Title:
- X-ray polarization predictions in blazars
- Short Name:
- J/ApJ/880/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray polarization should provide new probes of magnetic field geometry and acceleration physics near the base of blazar jets, but near-future missions will have limited sensitivity. We thus use existing lower energy data and X-ray variability measurements in the context of a basic synchro-Compton model to predict the X-ray polarization level and the probability of detection success for individual sources, listing the most attractive candidates for an Imaging X-ray Polarimetry Explorer campaign. We find that, as expected, several high-peak blazars such as Mrk 421 can be easily measured in 100ks exposures. Most low-peak sources should only be accessible to triggered campaigns during bright flares. Surprisingly, a few intermediate peak sources can have anomalously high X-ray polarization and thus are attractive targets.
- ID:
- ivo://CDS.VizieR/J/ApJ/376/161
- Title:
- X-ray spectra of bursting neutron stars
- Short Name:
- J/ApJ/376/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray burst sources represent a class of accreting neutron stars in close binary systems which do not exhibit any traces of the magnetic field. We present new method of hot model atmosphere computations with account of Compton scattering on free electrons and computed set of plane-parallel hydrogen-helium atmospheres and X-ray spectra of bursting neutron stars. Models were computed with precise angle-dependent radiative transfer under constrains of radiative and hydrostatic equilibrium. Compton scattering opacity included both the Klein-Nishina corrections and the effects of relativistic Maxwellian thermal motion of scattering electrons. Compton redistribution function allows for large energy exchange between X-ray photons and scattering electrons.
