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Start Over Subject white dwarf stars Content Level Research
81. Hot white dwarfs in GALEX-DR5
ID:
ivo://CDS.VizieR/J/MNRAS/411/2770
Title:
Hot white dwarfs in GALEX-DR5
Short Name:
J/MNRAS/411/2770
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present comprehensive catalogues of hot star candidates in the Milky Way (MW), selected from Galaxy Evolution Explorer (GALEX) far-UV (FUV; 1344-1786{AA}) and near-UV (NUV; 1771-2831{AA}) imaging. The FUV and NUV photometry allows us to extract the hottest stellar objects, in particular hot white dwarfs (WD), which are elusive at other wavelengths because of their high temperatures and faint optical luminosities. We generated catalogues of UV sources from two GALEX's surveys: All-Sky Imaging Survey (AIS; depth AB magnitude ~19.9/20.8 in FUV/NUV) and Medium-depth Imaging Survey (MIS; depth ~22.6/22.7mag). The two catalogues (from GALEX fifth data release) contain 65.3/12.6 million (AIS/MIS) unique UV sources with errorNUV<= 0.5 mag, over 21 435/1579deg^2^. We also constructed subcatalogues of the UV sources with matched optical photometry from Sloan Digital Sky Survey (SDSS; seventh data release): these contain 0.6/0.9 million (AIS/MIS) sources with errors <=0.3mag in both FUV and NUV, excluding sources with multiple optical counterparts, over an area of 7325/1103 deg2. All catalogues are available online. We then selected 28 319 (AIS)/9028 (MIS) matched sources with FUV-NUV<-0.13; this colour cut corresponds to stellar Teff hotter than ~18 000K (the exact value varying with gravity). An additional colour cut of NUV-r>0.1 isolates binaries with largely differing Teffs, and some intruding quasi-stellar objects (QSOs; more numerous at faint magnitudes). Available spectroscopy for a subsample indicates that hot-star candidates with NUV-r<0.1 (mostly 'single' hot stars) have negligible contamination by non-stellar objects. We discuss the distribution of sources in the catalogues, and the effects of error and colour cuts on the samples. The density of hot-star candidates increases from high to low Galactic latitudes, but drops on the MW plane due to dust extinction. Our hot-star counts at all latitudes are better matched by MW models computed with an initial-final mass relation (IFMR) that favours lower final masses. The model analysis indicates that the brightest sample is likely composed of WDs located in the thin disc, at typical distances between 0.15 and 1kpc, while the fainter sample comprises also a fraction of thick disc and halo stars. Proper motion distributions, available only for the bright sample (NUV<18mag), are consistent with the kinematics of a thin-disc population.
82. HST/COS observations of 7 white dwarfs
ID:
ivo://CDS.VizieR/J/ApJ/823/49
Title:
HST/COS observations of 7 white dwarfs
Short Name:
J/ApJ/823/49
Date:
21 Oct 2021
Publisher:
CDS
Description:
The search for transiting habitable exoplanets has broadened to include several types of stars that are smaller than the Sun in an attempt to increase the observed transit depth and hence the atmospheric signal of the planet. Of all spectral types, white dwarfs (WDs) are the most favorable for this type of investigation. The fraction of WDs that possess close-in rocky planets is unknown, but several large angle stellar surveys have the photometric precision and cadence to discover at least one if they are common. Ultraviolet observations of WDs may allow for detection of molecular oxygen or ozone in the atmosphere of a terrestrial planet. We use archival Hubble Space Telescope data from the Cosmic Origins Spectrograph to search for transiting rocky planets around UV-bright WDs. In the process, we discovered unusual variability in the pulsating WD GD 133, which shows slow sinusoidal variations in the UV. While we detect no planets around our small sample of targets, we do place stringent limits on the possibility of transiting planets, down to sub-lunar radii. We also point out that non-transiting small planets in thermal equilibrium are detectable around hotter WDs through infrared excesses, and identify two candidates.
83. Images of two DQ white dwarfs
ID:
ivo://CDS.VizieR/J/A+A/544/L6
Title:
Images of two DQ white dwarfs
Short Name:
J/A+A/544/L6
Date:
21 Oct 2021
Publisher:
CDS
Description:
The intensity profiles of the C2 Swan bands in cool DQ white dwarfs cannot be adequately fitted with models that otherwise succesfully reproduce spectral features of the molecule CH in these stars. Initial modelling showed that a two-component atmosphere in the style of a spot might be able to solve the problem. We photometrically observed the two cool DQ white dwarfs GJ1117 and EGGR78 to search for variability caused by stellar spots. We have not found any such variability, but we estimate the effects of hypothetical spots on lightcurves. We also estimate detection probabilities for spots in different configurations. Alternative explanations of the problem are needed and briefly discussed.
84. Impact of core and shell masses on SNe Ia
ID:
ivo://CDS.VizieR/J/A+A/649/A155
Title:
Impact of core and shell masses on SNe Ia
Short Name:
J/A+A/649/A155
Date:
22 Feb 2022
Publisher:
CDS
Description:
Sub-Chandrasekhar yield carbon-oxygen white dwarfs with a surface helium shell have been proposed as progenitors of Type Ia supernovae (SNe Ia). If true, the resulting thermonuclear explosions should be able to account for at least some of the range of SNe Ia observables. To study this, we conducted a parameter study based on three-dimensional simulations of double detonations in carbon-oxygen white dwarfs with a helium shell, assuming different core and shell yieldes. An admixture of carbon to the shell and solar metallicity are included in the models. The hydrodynamic simulations were carried out using the Arepo code. This allowed us to follow the helium shell detonation with high numerical resolution, and this improves the reliability of predicted nucleosynthetic shell detonation yields. The addition of carbon to the shell leads to a lower production of ^56^Ni, while including solar metallicity increases the production of intermediate yield elements. The production of higher mass elements is further shifted to stable isotopes at solar metallicity. Moreover, we find different core detonation ignition mechanisms depending on the core and shell yield configuration. This has an influence on the ejecta structure. We present the bolometric light curves predicted from our explosion simulations using the Monte Carlo radiative transfer code Artis and make comparisons with bolometric SNe Ia data. The bolometric light curves of our models show a range of brightnesses, which is able to account for subluminous to normal brightness SNe Ia. We show the model bolometric width-luminosity relation compared to data for a range of model viewing angles. We find that, on average, our brighter models lie within the observed data. The ejecta asymmetries produce a wide distribution of observables, which might account for outliers in the data. However, the models overestimate the extent of this compared to data. We also find that the bolometric decline rate over 40 days, {Delta}m_40_(bol), appears systematically faster than data.
85. Infrared photometry of DA white dwarfs from LAMOST
ID:
ivo://CDS.VizieR/J/AJ/146/34
Title:
Infrared photometry of DA white dwarfs from LAMOST
Short Name:
J/AJ/146/34
Date:
21 Oct 2021
Publisher:
CDS
Description:
A total of ~640000 objects from the LAMOST pilot survey have been publicly released. In this work, we present a catalog of DA white dwarfs (DAWDs) from the entire pilot survey. We outline a new algorithm for the selection of white dwarfs (WDs) by fitting Sersic profiles to the Balmer H{beta}, H{gamma}, and H{delta} lines of the spectra, and calculating the equivalent width of the CaII K line. Two thousand nine hundred sixty-four candidates are selected by constraining the fitting parameters and the equivalent width of the CaII K line. All the spectra of candidates are visually inspected. We identify 230 DAWDs (59 of which are already included in the Villanova and SDSS WD catalogs), 20 of which are DAWDs with non-degenerate companions. In addition, 128 candidates are classified as DAWDs/subdwarfs, which means the classifications are ambiguous. The result is consistent with the expected DAWD number estimated based on the LEGUE target selection algorithm.
86. Iron in hot DA white dwarfs
ID:
ivo://CDS.VizieR/J/ApJ/652/1554
Title:
Iron in hot DA white dwarfs
Short Name:
J/ApJ/652/1554
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of the iron abundance pattern in hot, hydrogen-rich (DA) white dwarfs. The study is based on new and archival far-ultraviolet spectroscopy of a sample of white dwarfs in the temperature range 30000K<=Teff<=64000K. The spectra obtained with the Far Ultraviolet Spectroscopic Explorer, along with spectra obtained with the Hubble Space Telescope Imaging Spectrograph and the International Ultraviolet Explorer, sample FeIII-FeVI absorption lines, enabling a detailed iron abundance analysis over a wider range of effective temperatures than previously afforded.
87. IR photometry of 2MASS/Spitzer white dwarfs
ID:
ivo://CDS.VizieR/J/ApJ/657/1013
Title:
IR photometry of 2MASS/Spitzer white dwarfs
Short Name:
J/ApJ/657/1013
Date:
21 Oct 2021
Publisher:
CDS
Description:
We review the available near- and mid-infrared photometry for white dwarfs obtained from the Two Micron All Sky Survey (2MASS) and by the Spitzer Space Telescope. Both data sets have recently been used to seek white dwarfs with infrared excesses due to the presence of unresolved companions or circumstellar disks, and also to derive the atmospheric parameters of cool white dwarfs. We first attempt to evaluate the reliability of the 2MASS photometry by comparing it with an independent set of published JHK CIT magnitudes for 160 cool white dwarf stars, and also by comparing the data with the predictions of detailed model atmosphere calculations. The possibility of using 2MASS to identify unresolved M dwarf companions or circumstellar disks is then discussed.
88. Isolated massive white dwarfs catalog
ID:
ivo://CDS.VizieR/J/A+A/420/507
Title:
Isolated massive white dwarfs catalog
Short Name:
J/A+A/420/507
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the catalogue of 112 massive isolated white dwarfs, both magnetic and nonmagnetic, with masses M>0.8M_{sun}_. Mass determinations and other parameters of white dwarfs were compiled from the available literature.
89. IUE echelle spectra of hot white dwarfs
ID:
ivo://CDS.VizieR/J/ApJS/119/207
Title:
IUE echelle spectra of hot white dwarfs
Short Name:
J/ApJS/119/207
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper summarizes the results obtained from a comprehensive analysis of all of the SWP echelle spectra of the white dwarf stars contained in the IUE Final Archive. A total of 209 NEWSIPS spectra of 55 degenerate stars of various types have been systematically reduced and analyzed. These include, in addition to conventional white dwarfs, several examples of the hot planetary nebula central stars such as NGC 246, which represent the initial stages of He-rich degenerate evolution. A representative summary of the stellar, circumstellar, and interstellar features found to be present in these spectra is presented. For 33 of the 55 stars, multiple spectra of sufficient quality exist so that co-added spectra with improved signal-to-noise ratio can be constructed. Much previously unrecognized detail and many new features are evident in these data. In addition, it was found necessary to apply several corrections to the NEWSIPS extracted spectra. These corrections, involving the wavelength scale and flux uncertainty vector, are described.
90. IUE low-dispersion spectra of white dwarfs
ID:
ivo://CDS.VizieR/J/ApJS/147/145
Title:
IUE low-dispersion spectra of white dwarfs
Short Name:
J/ApJS/147/145
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have produced an archive of the ultraviolet low-dispersion spectra for the full set of white dwarf stars observed with the International Ultraviolet Explorer (IUE) satellite over the course of its 18-yr mission. This archive contains the spectra of 322 individual degenerate stars which have been processed to optimize the signal-to- noise for each star. In particular, all spectra have been corrected for residual temporal and thermal effects and placed on the Hubble Space Telescope Faint Object Spectrograph absolute flux scale using procedures described by Massa & Fitzpatrick (2000ApJS..126..517M). Wherever possible, multiple observations of individual stars have been co-added to further enhance signal-to-noise and have been combined into a single spectrum including the full 1150 to 3150{AA} wavelength region observed by IUE. The contents of this spectral archive are described and the details of data reduction procedures are provided. The electronic files of the processed spectra are available, in FITS and ASCII formats, with the associated log file, at http://vega.lpl.arizona.edu/newsips/low/

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