ABSTRACT
We present a spectroscopic survey of 230 white dwarf candidates within 40 pc 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〉 = 6200 K), 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 ± 0.01 M⊙) 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 (δ > 0°) 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.
Abstract
An observational constraint on the contribution of double degenerates to Type Ia supernovae requires multiple radial velocity measurements of ideally thousands of white dwarfs. This is ...because only a small fraction of the double degenerate population is massive enough, with orbital periods short enough, to be considered viable Type Ia progenitors. We show how the radial velocity information available from public surveys such as the Sloan Digital Sky Survey can be used to pre-select targets for variability, leading to a 10-fold reduction in observing time required compared to an unranked or random survey. We carry out Monte Carlo simulations to quantify the detection probability of various types of binaries in the survey and show that this method, even in the most pessimistic case, doubles the survey size of the largest survey to date (the SPY Survey) in less than 15 per cent of the required observing time. Our initial follow-up observations corroborate the method, yielding 15 binaries so far (eight known and seven new), as well as orbital periods for four of the new binaries.
In preparation for the upcoming all-sky data releases of the Gaia mission we compiled a catalog of known hot subdwarf stars and candidates drawn from the literature and yet unpublished databases. The ...catalog contains 5613 unique sources and provides multi-band photometry from the ultraviolet to the far infrared, ground based proper motions, classifications based on spectroscopy and colors, published atmospheric parameters, radial velocities and light curve variability information. Using several different techniques we removed outliers and misclassified objects. By matching this catalog with astrometric and photometric data from the Gaia mission, we will develop selection criteria to construct a homogeneous, magnitude-limited all-sky catalog of hot subdwarf stars based on Gaia data.
ABSTRACT
White dwarfs with emission lines from gaseous debris discs are among the rarest examples of planetary remnant hosts, but at the same time they are key objects for studying the final ...evolutionary stage of planetary systems. Making use of the large number of white dwarfs identified in Gaia Data Release 2 (DR2), we are conducting a survey of planetary remnants and here we present the first results of our search: six white dwarfs with gaseous debris discs. This first publication focuses on the main observational properties of these objects and highlights their most unique features. Three systems in particular stand out: WD J084602.47+570328.64 displays an exceptionally strong infrared excess that defies the standard model of a geometrically thin, optically thick dusty debris disc; WD J213350.72+242805.93 is the hottest gaseous debris disc host known with $\mbox{$T_{\mathrm{eff}}$}=29\,282$ K; and WD J052914.32–340108.11 in which we identify a record number of 51 emission lines from five elements. These discoveries shed light on the underlying diversity in gaseous debris disc systems and bring the total number of these objects to 21. With these numbers we can now start looking at the properties of these systems as a class of objects rather than on a case-by-case basis.
Abstract LP 40–365 (aka GD 492) is a nearby low-luminosity hyper-runaway star with an extremely unusual atmospheric composition, which has been proposed as the remnant of a white dwarf that survived ...a peculiar Type Iax supernova (SN Iax) in a single-degenerate scenario. Adopting the Gaia Data Release 2 (DR2) parallax, ϖ = 1.58 ± 0.03 mas, we estimate a radius of 0.18 ± 0.01 R⊙, confirming LP 40–365 as a subluminous star that is ≃ 15 times larger than a typical white dwarf and is compatible with the SN Iax remnant scenario. We present an updated kinematic analysis, making use of the Gaia parallax and proper motion, and confirm that LP 40–365 is leaving the Milky Way at about 1.5 times the escape velocity of the Solar neighbourhood with a rest-frame velocity of 852 ± 10 km s−1. Integrating the past trajectories of LP 40–365, we confirm that it crossed the Galactic disc 5.3 ± 0.5 Myr ago in the direction of Carina, likely coming from beneath the plane. Finally, we estimate that LP 40–365 was ejected from its progenitor binary with a velocity of at least 600 km s−1, which is compatible with theoretical predictions for close binaries containing a white dwarf and a helium-star donor.
The AM Canum Venaticorum (AM CVn) binaries are a rare group of ultrashort period, mass-transferring white dwarf binaries, some of which may be Type Ia supernova progenitors. More than a third of the ...total known population of AM CVn binaries have been discovered via the Sloan Digital Sky Survey (SDSS). Here, we discuss our search for new AM CVns in the SDSS spectroscopic data base, and present two new AM CVns discovered in SDSS-III spectroscopy, SDSS J113732.32+405458.3 and SDSS J150551.58+065948.7. The AM CVn binaries exhibit a connection between their spectral appearance and their orbital period, the spectra of these two new AM CVns suggest that they may be long-period systems. Using the radial velocity variations of the emission lines, we measure a possible orbital period of 59.6 ± 2.7 min for SDSS J113732.32+405458.3. Since our search of SDSS spectroscopy has revealed only these two new systems, it is unlikely that a large population of AM CVn binaries have been missed, and their discovery should have little effect on previous calculations of the AM CVn space density.
Aims.
We estimated the spectral evolution of white dwarfs with effective temperature using the Javalambre Photometric Local Universe Survey (J-PLUS) second data release (DR2), which provides 12 ...photometric optical passbands over 2176 deg
2
.
Methods.
We analyzed 5926 white dwarfs with
r
≤ 19.5 mag in common between a white dwarf catalog defined from
Gaia
EDR3 and J-PLUS DR2. We performed a Bayesian analysis by comparing the observed J-PLUS photometry with theoretical models of hydrogen- and helium-dominated atmospheres. We estimated the probability distribution functions for effective temperature (
T
eff
), surface gravity, parallax, and composition; and the probability of having a H-dominated atmosphere (
p
H
) for each source. We applied a prior in parallax, using
Gaia
EDR3 measurements as a reference, and derived a self-consistent prior for the atmospheric composition as a function of
T
eff
.
Results.
We described the fraction of white dwarfs with a He-dominated atmosphere (
f
He
) with a linear function of the effective temperature at 5000 <
T
eff
< 30 000 K. We find
f
He
= 0.24 ± 0.01 at
T
eff
= 10 000 K, a change rate along the cooling sequence of 0.14 ± 0.02 per 10 kK, and a minimum He-dominated fraction of 0.08 ± 0.02 at the high-temperature end. We tested the obtained
p
H
by comparison with spectroscopic classifications, finding that it is reliable. We estimated the mass distribution for the 351 sources with distance
d
< 100 pc, mass
M
> 0.45
M
⊙
, and
T
eff
> 6000 K. The result for H-dominated white dwarfs agrees with previous studies, with a dominant
M
= 0.59
M
⊙
peak and the presence of an excess at
M
∼ 0.8
M
⊙
. This high-mass excess is absent in the He-dominated distribution, which presents a single peak.
Conclusions.
The J-PLUS optical data provide a reliable statistical classification of white dwarfs into H- and He-dominated atmospheres. We find a 21 ± 3% increase in the fraction of He-dominated white dwarfs from
T
eff
= 20 000 K to
T
eff
= 5000 K.
ABSTRACT
SDSS-V is carrying out a dedicated survey for white dwarfs, single, and in binaries, and we report the analysis of the spectroscopy of 118 cataclysmic variables (CVs) and CV candidates ...obtained during the final plug plate observations of SDSS. We identify eight new CVs, spectroscopically confirm 53 and refute 11 published CV candidates, and we report 21 new or improved orbital periods. The orbital period distribution of the SDSS-V CVs does not clearly exhibit a period gap. In common with previous studies, the distribution shows that spectroscopically identified CVs have a larger proportion of short-period systems compared to samples identified from photometric variability. Remarkably, despite a systematic search, we find very few period bouncers. We estimate the space density of period bouncers to be $\simeq 0.2\times 10^{-6}\, \mathrm{pc}^{-3}$, i.e. they represent only a few per cent of the total CV population. This suggests that during their final phase of evolution, CVs either destroy the donor, e.g. via a merger, or that they become detached and cease mass transfer.
In previous work by Gentile Fusillo et al., we developed a selection method for white dwarf candidates which makes use of photometry, colours and proper motions to calculate a probability of being a ...white dwarf (P
WD). The application of our method to the Sloan Digital Sky Survey (SDSS) data release 10 resulted in ≃66 000 photometrically selected objects with a derived P
WD, approximately ≃21 000 of which are high-confidence white dwarf candidates. Here, we present an independent test of our selection method based on a sample of spectroscopically confirmed white dwarfs from the Large Sky Area Multi-Fiber Spectroscopic Telescope (LAMOST) survey. We do this by cross-matching all our ≃66 000 SDSS photometric white dwarf candidates with the over 4 million spectra available in the third data release of LAMOST. This results in 1673 white dwarf candidates with no previous SDSS spectroscopy, but with available LAMOST spectra. Among these objects, we identify 309 genuine white dwarfs. We find that our P
WD can efficiently discriminate between confirmed LAMOST white dwarfs and contaminants. Our white dwarf candidate selection method can be applied to any multiband photometric survey and in this work we conclusively confirm its reliability in selecting white dwarfs without recourse to spectroscopy. We also discuss the spectroscopic completeness of white dwarfs in LAMOST, as well as deriving effective temperatures, surface gravities and masses for the hydrogen-rich atmosphere white dwarfs in the newly identified LAMOST sample.
We report on the identification of 22 new cool DO-type white dwarfs (WDs) detected in data release 10 (DR10) of the Sloan Digital Sky Survey (SDSS). Among them, we found one more member of the ...so-called hot-wind DO WDs, which show ultrahigh excitation absorption lines. Our non-LTE model atmosphere analyses of these objects and two not previously analyzed hot-wind DO WDs, revealed effective temperatures and gravities in the ranges Teff = 45−80 kK and log g = 7.50−8.75. In eight of the spectra we found traces of C (0.001−0.01, by mass). Two of these are the coolest DO WDs ever discovered that still show a considerable amount of C in their atmospheres. This is in strong contradiction with diffusion calculations, and probably, similar to what is proposed for DB WDs, a weak mass-loss is present in DO WDs. One object is the most massive DO WD discovered so far with a mass of 1.07 M⊙ if it is an ONe-WD or 1.09 M⊙ if it is a CO-WD. We furthermore present the mass distribution of all known hot non-DA (pre-) WDs and derive the hot DA to non-DA ratio for the SDSS DR7 spectroscopic sample. The mass distribution of DO WDs beyond the wind limit strongly deviates from the mass distribution of the objects before the wind limit. We address this phenomenon by applying different evolutionary input channels. We argue that the DO WD channel may be fed by about 13% by post-extreme-horizontal branch stars and that PG 1159 stars and O(He) stars may contribute in a similar extent to the non-DA WD channel.
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