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31. Cool white dwarfs in the solar neighborhood
ID:
ivo://CDS.VizieR/J/ApJ/643/402
Title:
Cool white dwarfs in the solar neighborhood
Short Name:
J/ApJ/643/402
Date:
21 Oct 2021
Publisher:
CDS
Description:
The New Luyten Two-Tenths catalog contains a large number of high proper motion white dwarf candidates that remain to be spectroscopically confirmed. We present new spectroscopic observations, as well as SDSS archival spectra of 49 white dwarf candidates selected from the revised NLTT catalog of Salim & Gould (2003, Cat. J/ApJ/582/1011). Of these, 34 are cool DA white dwarfs with temperatures ranging from approximately 5000 up to 11,690K, and 11 are DC white dwarfs with temperatures ranging from 4300K (NLTT 18555) up to 11000K. Three of the DA white dwarfs also display abundances of heavy elements (NLTT 3915, NLTT 44986, and NLTT 43806), and one is a cool magnetic white dwarf (NLTT 44447) with an estimated magnetic field strength of 1.3MG. We also present a new cool DQ white dwarf (NLTT 31347) with an estimated temperature of 6250K. We supplement our sample with SDSS ugriz photometry for a fraction of the newly identified white dwarfs. A kinematical study of this sample of white dwarfs, characterized by proper motions ranging from 0.136"/yr to 0.611"/yr, suggest that they belong to the thin disk population.
32. DA-white dwarfs from SDSS and UKIDSS
ID:
ivo://CDS.VizieR/J/MNRAS/417/1210
Title:
DA-white dwarfs from SDSS and UKIDSS
Short Name:
J/MNRAS/417/1210
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a method which uses colour-colour cuts on the Sloan Digital Sky Survey (SDSS) photometry to select white dwarfs with hydrogen-rich (DA) atmospheres without the recourse to spectroscopy. This method results in a sample of DA white dwarfs that is 95 per cent complete at an efficiency of returning a true DA white dwarf of 62 per cent. The approach was applied to SDSS Data Release 7 for objects with and without SDSS spectroscopy.
33. DA white dwarfs from the Palomar Green Survey
ID:
ivo://CDS.VizieR/J/ApJS/156/47
Title:
DA white dwarfs from the Palomar Green Survey
Short Name:
J/ApJS/156/47
Date:
21 Oct 2021
Publisher:
CDS
Description:
Spectrophotometric observations at high signal-to-noise ratio were obtained of a complete sample of 347 DA white dwarfs from the Palomar Green (PG) Survey (1986, Cat. <II/207>). Fits of observed Balmer lines to synthetic spectra calculated from pure-hydrogen model atmospheres were used to obtain robust values of T_eff_, log(g), masses, radii, and cooling ages. The luminosity function of the sample, weighted by 1/V_max_, was obtained and compared with other determinations.
34. DA white dwarfs in 2dF QSO Redshift Survey
ID:
ivo://CDS.VizieR/J/MNRAS/335/673
Title:
DA white dwarfs in 2dF QSO Redshift Survey
Short Name:
J/MNRAS/335/673
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the spectroscopic identification of close to 1000 hydrogen-rich (DA) white dwarfs discovered in the course of the Anglo-Australian 2dF QSO Redshift Survey (2QZ, Cat. <VII/223>). We measured the atmospheric parameters of a subsample of 201 stars based on good-quality Balmer line spectra and we determine the 2QZ population characteristics. Over ten per cent of the sample are potential ZZ Ceti variables. We estimate the DA white dwarf birthrate (b_DA_=0.5-1.0x10^-12^/yr/pc^3^) and the scale-height (h=220-300pc) of the population in the thin disc of the Galaxy by combining information acquired in the Palomar-Green, AAT-UVX and new 2QZ surveys. White dwarfs appear related to G and late-F progenitors. A catalogue of 201 DA white dwarfs is presented.
35. DA white dwarfs infrared photometry
ID:
ivo://CDS.VizieR/J/ApJ/760/26
Title:
DA white dwarfs infrared photometry
Short Name:
J/ApJ/760/26
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present near- and mid-infrared photometry and spectroscopy from PAIRITEL, IRTF, and Spitzer of a metallicity-unbiased sample of 117 cool, hydrogen-atmosphere white dwarfs (WDs) from the Palomar-Green survey and find five with excess radiation in the infrared, translating to a 4.3^+2.7^_-1.2_% frequency of debris disks. This is slightly higher than, but consistent with the results of previous surveys. Using an initial-final mass relation, we apply this result to the progenitor stars of our sample and conclude that 1-7M_{sun}_ stars have at least a 4.3% chance of hosting planets; an indirect probe of the intermediate-mass regime eluding conventional exoplanetary detection methods. Alternatively, we interpret this result as a limit on accretion timescales as a fraction of WD cooling ages; WDs accrete debris from several generations of disks for ~10Myr. The average total mass accreted by these stars ranges from that of 200km asteroids to Ceres-sized objects, indicating that WDs accrete moons and dwarf planets as well as solar system asteroid analogs.
36. DB white dwarfs from the Hamburg/ESO survey
ID:
ivo://CDS.VizieR/J/A+A/363/1040
Title:
DB white dwarfs from the Hamburg/ESO survey
Short Name:
J/A+A/363/1040
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an analysis of 40 cool helium-rich white dwarfs found in the Hamburg/ESO survey. They were selected for follow-up spectroscopy because of their U-B colour below -0.18, the absence of strong absorption lines, and a continuum shape similar to that of a quasar. Effective temperatures for individual stars were determined by fitting model atmospheres of nearly pure helium with a small admixture of hydrogen. As a consequence of the selection criteria all but one sample stars have T_eff_ below 20000K. Four stars clearly show helium and hydrogen lines in their spectra. In the spectra of another three, helium, hydrogen, and metal lines can be detected. For these stars hydrogen and metal abundances were also determined by fitting appropriate model atmospheres containing these elements. Seven sample stars most likely have helium-rich atmospheres but do not show any helium lines. They either have featureless spectra or show calcium lines.
37. DB white dwarfs in SDSS DR10 and DR12
ID:
ivo://CDS.VizieR/J/A+A/583/A86
Title:
DB white dwarfs in SDSS DR10 and DR12
Short Name:
J/A+A/583/A86
Date:
21 Oct 2021
Publisher:
CDS
Description:
White dwarfs with helium-dominated atmospheres (spectral types DO, DB) comprise approximately 20% of all white dwarfs. There are fewer studies than of their hydrogen-rich counterparts (DA) and thus several questions remain open. Among these are the total masses and the origin of the hydrogen traces observed in a large number and the nature of the deficit of DBs in the range from 30000-45000K. We use the largest-ever sample (by a factor of 10) provided by the Sloan Digital Sky Survey (SDSS) to study these questions. The photometric and spectroscopic data of 1107 helium-rich objects from the SDSS are analyzed using theoretical model atmospheres. Along with the effective temperature and surface gravity, we also determine hydrogen and calcium abundances or upper limits for all objects. The atmosphere models are extended with envelope calculations to determine the extent of the helium convection zones and thus the total amount of hydrogen and calcium present.
38. DB white dwarfs with SDSS and Gaia data
ID:
ivo://CDS.VizieR/J/ApJ/882/106
Title:
DB white dwarfs with SDSS and Gaia data
Short Name:
J/ApJ/882/106
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a comprehensive analysis of DB white dwarfs drawn from the Sloan Digital Sky Survey, based on model fits to ugriz photometry and medium-resolution spectroscopy from the Sloan Digital Sky Survey. We also take advantage of the exquisite trigonometric parallax measurements recently obtained by the Gaia mission. Using the so-called photometric and spectroscopic techniques, we measure the atmospheric and physical parameters of each object in our sample (Teff, logg, H/He, Ca/He, R, M), and compare the values obtained from both techniques in order to assess the precision and accuracy of each method. We then explore in great detail the surface gravity, stellar mass, and hydrogen abundance distributions of DB white dwarfs as a function of effective temperature. We present some clear evidence for a large population of unresolved double-degenerate binaries composed of DB+DB and even DB+DA white dwarfs. In the light of our results, we finally discuss the spectral evolution of DB white dwarfs, in particular the evolution of the DB-to-DA ratio as a function of Teff, and we revisit the question of the origin of hydrogen in DBA white dwarfs.
39. Detailed analysis of cool WDs in the SDSS
ID:
ivo://CDS.VizieR/J/ApJS/190/77
Title:
Detailed analysis of cool WDs in the SDSS
Short Name:
J/ApJS/190/77
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present optical spectroscopy and near-infrared photometry of 126 cool white dwarfs (WDs) in the Sloan Digital Sky Survey (SDSS DR3). Our sample includes high proper motion targets selected using the SDSS and USNO-B astrometry and a dozen previously known ultracool WD candidates. Our optical spectroscopic observations demonstrate that a clean selection of large samples of cool WDs in the SDSS (and the SkyMapper, Pan-STARRS, and the Large Synoptic Survey Telescope data sets) is possible using a reduced proper motion diagram and a tangential velocity cut-off (depending on the proper motion accuracy) of 30km/s. Our near-infrared observations reveal eight new stars with significant absorption. We use the optical and near-infrared photometry to perform a detailed model atmosphere analysis. More than 80% of the stars in our sample are consistent with either pure hydrogen or pure helium atmospheres. However, the eight stars with significant infrared absorption and the majority of the previously known ultracool WD candidates are best explained with mixed hydrogen and helium atmosphere models. The age distribution of our sample is consistent with a Galactic disk age of 8Gyr. A few ultracool WDs may be as old as 12-13Gyr, but our models have problems matching the spectral energy distributions of these objects. There are only two halo WD candidates in our sample. However, trigonometric parallax observations are required for accurate mass and age determinations and to confirm their membership in the halo.
40. Distances of white dwarf stars
ID:
ivo://CDS.VizieR/J/ApJ/571/512
Title:
Distances of white dwarf stars
Short Name:
J/ApJ/571/512
Date:
21 Oct 2021
Publisher:
CDS
Description:
The most recent version of the Catalog of Spectroscopically Identified White Dwarfs lists 2249 white dwarf stars. Among these stars are 109 white dwarfs that have either reliable trigonometric parallaxes or color-based distance moduli that place them at a distance within 20pc of the Sun. Most of these nearby white dwarfs are isolated stars, but 28 (25% of the sample) are in binary systems, including such well-known systems as Sirius A/B and Procyon A/B. There are also three double degenerate systems in this sample of the local white dwarf population. The sample of local white dwarfs is largely complete out to 13pc, and the local density of white dwarf stars is found to be 5.0+/-0.7x10^-3^pc^-3^, with a corresponding mass density of 3.4+/-0.5x10^-3^M{sun}_/pc^3^

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