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We present a comprehensive overview of a volume-complete sample of white dwarfs located within 40 pc of the Sun, a significant proportion of which were detected in Gaia Data Release 3 (DR3). Our DR3 sample contains 1076 spectroscopically confirmed white dwarfs, with just five candidates within the volume remaining unconfirmed (> 99 per cent spectroscopic completeness). Additionally, 28 white dwarfs were not in our initial selection from Gaia DR3, most of which are in unresolved binaries. We use Gaia DR3 photometry and astrometry to determine a uniform set of white dwarf parameters, including mass, effective temperature, and cooling age. We assess the demographics of the 40 pc sample, specifically magnetic fields, binarity, space density, and mass distributions.

 

ABSTRACT We present an analysis of the most massive white dwarf candidates in the Montreal White Dwarf Database 100 pc sample. We identify 25 objects that would be more massive than $1.3\, {\rm M}_{\odot }$ if they had pure H atmospheres and CO cores, including two outliers with unusually high photometric mass estimates near the Chandrasekhar limit. We provide follow-up spectroscopy of these two white dwarfs and show that they are indeed significantly below this limit. We expand our model calculations for CO core white dwarfs up to M = 1.334 M⊙, which corresponds to the high-density limit of our equation-of-state tables, ρ = 109 g cm−3. We find many objects close to this maximum mass of our CO core models. A significant fraction of ultramassive white dwarfs are predicted to form through binary mergers. Merger populations can reveal themselves through their kinematics, magnetism, or rapid rotation rates. We identify four outliers in transverse velocity, four likely magnetic white dwarfs (one of which is also an outlier in transverse velocity), and one with rapid rotation, indicating that at least 8 of the 25 ultramassive white dwarfs in our sample are likely merger products. 

ABSTRACT We present high-resolution spectroscopy of two nearby white dwarfs with inconsistent spectroscopic and parallax distances. The first one, PG 1632+177, is a 13th magnitude white dwarf only 25.6 pc away. Previous spectroscopic observations failed to detect any radial velocity changes in this star. Here, we show that PG 1632+177 is a 2.05-d period double-lined spectroscopic binary (SB2) containing a low-mass He-core white dwarf with a more-massive, likely CO-core white dwarf companion. After L 870−2, PG 1632+177 becomes the second closest SB2 white dwarf currently known. Our second target, WD 1534+503, is also an SB2 system with an orbital period of 0.71 d. For each system, we constrain the atmospheric parameters of both components through a composite model-atmosphere analysis. We also present a new set of non-local thermodynamic equilibrium (NLTE) synthetic spectra appropriate for modelling high-resolution observations of cool white dwarfs, and show that NLTE effects in the core of the H α line increase with decreasing effective temperature. We discuss the orbital period and mass distribution of SB2 and eclipsing double white dwarfs with orbital constraints, and demonstrate that the observed population is consistent with the predicted period distribution from the binary population synthesis models. The latter predict more massive CO + CO white dwarf binaries at short (<1 d) periods, as well as binaries with several day orbital periods; such systems are still waiting to be discovered in large numbers. 

ABSTRACT We present radial velocity observations of four binary white dwarf candidates identified through their overluminosity. We identify two new double-lined spectroscopic binary systems, WD 0311–649 and WD 1606+422, and constrain their orbital parameters. WD 0311–649 is a 17.7 h period system with a mass ratio of 1.44 ± 0.06 and WD 1606+422 is a 20.1 h period system with a mass ratio of 1.33 ± 0.03. An additional object, WD 1447–190, is a 43 h period single-lined white dwarf binary, whereas WD 1418–088 does not show any significant velocity variations over time-scales ranging from minutes to decades. We present an overview of the 14 overluminous white dwarfs that were identified by Bédard et al., and find the fraction of double- and single-lined systems to be both 31 per cent. However, an additional 31 per cent of these overluminous white dwarfs do not show any significant radial velocity variations. We demonstrate that these must be in long-period binaries that may be resolved by Gaia astrometry. We also discuss the overabundance of single low-mass white dwarfs identified in the SPY survey, and suggest that some of those systems are also likely long-period binary systems of more massive white dwarfs.