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Start Over Subject white dwarf stars Content Level Research
61. FUV-NUV observations of NGC 2808
ID:
ivo://CDS.VizieR/J/ApJ/625/156
Title:
FUV-NUV observations of NGC 2808
Short Name:
J/ApJ/625/156
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a reanalysis of far-ultraviolet (FUV) observations of the globular cluster NGC 2808 obtained with the Hubble Space Telescope. These data were first analyzed by Brown and coworkers (2001, Cat. <J/ApJ/562/368>), with an emphasis on the bright, blue horizontal-branch (HB) stars in this cluster. Here, our focus is on the population of fainter FUV sources, which include white dwarfs (WDs), blue stragglers (BSs), and cataclysmic variables (CVs).
62. Gaia DR1 mass-radius relation of white dwarfs
ID:
ivo://CDS.VizieR/J/MNRAS/465/2849
Title:
Gaia DR1 mass-radius relation of white dwarfs
Short Name:
J/MNRAS/465/2849
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Gaia Data Release 1 (DR1) sample of white dwarf parallaxes is presented, including six directly observed degenerates and 46 white dwarfs in wide binaries. This data set is combined with spectroscopic atmospheric parameters to study the white dwarf mass-radius relationship (MRR). Gaia parallaxes and G magnitudes are used to derive model atmosphere-dependent white dwarf radii, which can then be compared to the predictions of a theoretical MRR. We find a good agreement between Gaia DR1 parallaxes, published effective temperatures (T_eff_) and surface gravities (logg), and theoretical MRRs. As it was the case for Hipparcos, the precision of the data does not allow for the characterization of hydrogen envelope masses. The uncertainties on the spectroscopic atmospheric parameters are found to dominate the error budget and current error estimates for well-known and bright white dwarfs may be slightly optimistic. With the much larger Gaia DR2 white dwarf sample, it will be possible to explore the MRR over a much wider range of mass, T_eff_, and spectral types.
63. Gaia DR2 white dwarf candidates
ID:
ivo://CDS.VizieR/J/MNRAS/482/4570
Title:
Gaia DR2 white dwarf candidates
Short Name:
J/MNRAS/482/4570
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalogue of white dwarf candidates selected from the second data release of Gaia (DR2). We used a sample of spectroscopically confirmed white dwarfs from the Sloan Digital Sky Survey (SDSS) to map the entire space spanned by these objects in the Gaia Hertzsprung-Russell diagram. We then defined a set of cuts in absolute magnitude, colour, and a number of Gaia quality flags to remove the majority of contaminating objects. Finally, we adopt a method analogous to the one presented in our earlier SDSS photometric catalogues to calculate a probability of being a white dwarf (PWD) for all Gaia sources which passed the initial selection. The final catalogue is composed of 486641 stars with calculated PWD from which it is possible to select a sample of~260000 high-confidence white dwarf candidates in the magnitude range 8<G<21. By comparing this catalogue with a sample of SDSS white dwarf candidates we estimate an upper limit in completeness of 85 per cent for white dwarfs with G<=20mag and Teff>7000K, at high Galactic latitudes (|b|>20deg). However, the completeness drops at low Galactic latitudes, and the magnitude limit of the catalogue varies significantly across the sky as a function of Gaia's scanning law. We also provide the list of objects within our sample with available SDSS spectroscopy.
64. 723 Gaia DR2 White dwarfs cand. in Local Galactic Halo
ID:
ivo://CDS.VizieR/J/ApJ/899/83
Title:
723 Gaia DR2 White dwarfs cand. in Local Galactic Halo
Short Name:
J/ApJ/899/83
Date:
14 Mar 2022 08:58:44
Publisher:
CDS
Description:
We present a catalog of 531 white dwarf candidates that have large apparent transverse motions relative to the Sun (v_T_>200km/s), thus making them likely members of the local Galactic halo population. The candidates were selected from the Gaia Data Release 2 and are located in a great circle with 20{deg} width running across both Galactic poles and the Galactic center and anticenter, a zone that spans 17.3% of the sky. The selection used a combination of kinematic and photometric properties, derived primarily from Gaia proper motions, G magnitudes, and G_BP_-G_RP_ color, and including parallax whenever available. Additional validation of the white dwarf candidates is made using PanSTARRS photometric (gri) data. Our final catalog includes not only stars having full kinematic and luminosity estimates from reliable Gaia parallax, but also stars with presently unreliable or no available Gaia parallax measurements. We argue that our method of selecting local halo objects with and without reliable parallax data leads us to round up all possible halo white dwarfs in the Gaia catalog (in that particular section of the sky) with recorded proper motions >40mas/yr and that pass our v_T_>200km/s threshold requirement. We expect this catalog will be useful for the study of the white dwarf population of the local Galactic halo.
65. Gaia photometry for white dwarfs
ID:
ivo://CDS.VizieR/J/A+A/565/A11
Title:
Gaia photometry for white dwarfs
Short Name:
J/A+A/565/A11
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Gaia space mission, through its 5-6 years survey of the whole sky up to magnitude V=20-25, will drastically increase the sample of known white dwarfs allowing to address new science questions. In this paper we provide a characterisation of Gaia photometry for the case of white dwarfs to better prepare for the analysis of the scientific output of the mission including relationships among colours involving Gaia magnitudes (white light G, blue GBP, red GRP and GRVS passbands) and colours from other commonly used photometric systems (Johnson-Cousins, SDSS and 2MASS). We also present numbers of white dwarfs predicted by the Gaia Universe Model Snapshot and compare them with an alternative simulation calibrated with the local white dwarfs sample. In these online tables we provide the values used to fit the relationships in the paper, especially useful for those cases where the deviation from the established relationships is large. The most recent Gaia transmission curves and three different compositions for white dwarfs were considered here (pure hydrogen, pure helium and mixed composition with H/He=0.1).
66. Gaia stars with GALEX NUV excess
ID:
ivo://CDS.VizieR/J/other/RMxAA/53.439
Title:
Gaia stars with GALEX NUV excess
Short Name:
J/other/RMxAA/53
Date:
21 Oct 2021
Publisher:
CDS
Description:
Accurate parallaxes from Gaia DR1 (TGAS) are combined with GALEX visual Nuv magnitudes to produce absolute MNUV magnitudes and an ultraviolet HR diagram for a large sample of astrometric stars. A functional fit is derived of the lower envelope main sequence of the nearest 1403 stars (distance <40pc), which should be reddening-free. Using this empirical fit, 50 nearby stars are selected with significant Nuv excess. These are predominantly late K and early M dwarfs, often associated with X-ray sources, and showing other manifestations of magnetic activity. The sample may include systems with hidden white dwarfs, stars younger than the Pleiades, or, most likely, tight interacting binaries of the BY Dra-type. A separate collection of 40 stars with precise trigonometric parallaxes and Nuv-G colors bluer than 2mag is presented. It includes several known novae, white dwarfs, and binaries with hot subdwarf (sdOB) components, but most remain unexplored.
67. Gaia white dwarfs within 40pc. I
ID:
ivo://CDS.VizieR/J/MNRAS/497/130
Title:
Gaia white dwarfs within 40pc. I
Short Name:
J/MNRAS/497/130
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a spectroscopic survey of 230 white dwarf candidates within 40pc of the Sun from the William Herschel Telescope and Gran Telescopio Canarias. All candidates were selected from Gaia Data Release 2 (DR2) and in almost all cases, had no prior spectroscopic classifications. We find a total of 191 confirmed white dwarfs and 39 main-sequence star contaminants. The majority of stellar remnants in the sample are relatively cool (<Teff>=6200K), showing either hydrogen Balmer lines or a featureless spectrum, corresponding to 89 DA and 76 DC white dwarfs, respectively. We also recover two DBA white dwarfs and 9-10 magnetic remnants. We find two carbon-bearing DQ stars and 14 new metal-rich white dwarfs. This includes the possible detection of the first ultra-cool white dwarf with metal lines. We describe three DZ stars for which we find at least four different metal species, including one that is strongly Fe- and Ni-rich, indicative of the accretion of a planetesimal with core-Earth composition. We find one extremely massive (1.31+/-0.01M_{sun}_) DA white dwarf showing weak Balmer lines, possibly indicating stellar magnetism. Another white dwarf shows strong Balmer line emission but no infrared excess, suggesting a low-mass sub-stellar companion. A high spectroscopic completeness (>99 per cent) has now been reached for Gaia DR2 sources within 40-pc sample, in the Northern hemisphere ({delta}>0{deg} and located on the white dwarf cooling track in the Hertzsprung-Russell diagram. A statistical study of the full northern sample is presented in a companion paper (McCleery et al., Paper II, 2020MNRAS.499.1890M, Cat. J/MNRAS/499/1890).
68. Gaia white dwarfs within 40pc. II.
ID:
ivo://CDS.VizieR/J/MNRAS/499/1890
Title:
Gaia white dwarfs within 40pc. II.
Short Name:
J/MNRAS/499/1890
Date:
14 Jan 2022 00:10:10
Publisher:
CDS
Description:
We present an overview of the sample of northern hemisphere white dwarfs within 40pc of the Sun detected from Gaia Data Release 2 (DR2). We find that 521 sources are spectroscopically confirmed degenerate stars, 111 of which were first identified as white dwarf candidates from Gaia DR2 and followed-up recently with the William Herschel Telescope and Gran Telescopio Canarias. Three additional white dwarf candidates remain spectroscopically unobserved and six unresolved binaries are known to include a white dwarf but were not in our initial selection in the Gaia DR2 Hertzsprung-Russell diagram (HRD). Atmospheric parameters are calculated from Gaia and Pan-STARRS photometry for all objects in the sample, confirming most of the trends previously observed in the much smaller 20pc sample. Local white dwarfs are overwhelmingly consistent with Galactic disc kinematics, with only four halo candidates. We find that DAZ white dwarfs are significantly less massive than the overall DA population (MDAZ_avg_=0.59M_{sun}_, MDA_avg_=0.66M_{sun}_). It may suggest that planet formation is less efficient at higher mass stars, producing more massive white dwarfs. We detect a sequence of crystallised white dwarfs in the mass range from 0.6<=M/M_{sun}_<=1.0 and find that the vast majority of objects on the sequence have standard kinematic properties that correspond to the average of the sample, suggesting that their nature can be explained by crystallisation alone. We also detect 26 double degenerates and white dwarf components in 56 wide binary systems.
69. GALEX spectral database correction with IUE SEDs
ID:
ivo://CDS.VizieR/J/AJ/157/107
Title:
GALEX spectral database correction with IUE SEDs
Short Name:
J/AJ/157/107
Date:
21 Oct 2021
Publisher:
CDS
Description:
The CALSPEC database of absolute spectral energy distributions (SEDs) from the Hubble Space Telescope is based on pure hydrogen model atmosphere calculations for three unreddened white dwarf stars and represents the current UV flux calibration standard with a precision approaching 1% for well observed stars. Following our previous work to correct International Ultraviolet Explorer (IUE) fluxes, this paper provides an average correction for the Galaxy Evolution Explorer (GALEX) spectral database that places GALEX fluxes on the current CALSPEC scale. Our correction is derived by comparing GALEX spectroscopic flux distributions with CALSPEC and corrected IUE SEDs. This recalibration is relevant for any project based on GALEX archival spectroscopic data, e.g., UV or multi-wavelength analyses, correlating GALEX spectra with other existing or future databases, and planning of new observations. The recalibration will be applied to our planned catalog of corrected GALEX SEDs.

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