A white dwarf catalogue from Gaia-DR2 and the Virtual Observatory

Abstract

We present a catalogue of 73,221 white dwarf candidates extracted from the astrometric and photometric data of the recently published Gaia DR2 catalogue. White dwarfs were selected from the Gaia Hertzsprung-Russell diagram with the aid of the most updated population synthesis simulator. Our analysis shows that Gaia has virtually identified all white dwarfs within 100 pc from the Sun. Hence, our sub-population of 8,555 white dwarfs within this distance limit and the colour range considered, − 0.52 < (G BP − G RP ) < 0.80, is the largest and most complete volume-limited sample of such objects to date. From this sub-sample we identified 8,343 CO-core and 212 ONe-core white dwarf candidates and derived a white dwarf space density of 4.9±0.4×10 −3 pc −3 . A bifurcation in the Hertzsprung-Russell diagram for these sources, which our models do not predict, is clearly visible. We used the Virtual Observatory tool VOSA to derive effective temperatures and luminosities for our sources by fitting their spectral energy distributions, that we built from the UV to the NIR using publicly available photometry through the Virtual Observatory. From these parameters, we derived the white dwarf radii. Interpolating the radii and effective temperatures in hydrogen-rich white dwarf cooling sequences, we derived the surface gravities and masses. The Gaia 100 pc white dwarf population is clearly dominated by cool (∼ 8,000 K) objects and reveals a significant population of massive (M ∼ 0.8M ) white dwarfs, of which no more than ∼ 30−40 % can be attributed to hydrogen-deficient atmospheres, and whose origin remains uncertain.

Random Forest identification of the thin disc, thick disc, and halo Gaia-DR2 white dwarf population

“…This ratio results in a proportion 77:17:6 for the thin disc, thick disc, and halo white dwarfs, respectively, in good agreement with the estimates by . The simulated white dwarf sample is then normalized to the local space density of white dwarfs of 4.9 × 10 −3 pc −3 as estimated by Jiménez-Esteban et al (2018). Finally, and in order to reproduce the observational uncertainties, we introduce a photometric and an astrometric error for each of our simulated objects based on Gaia's performance 2 .…”

Evidence for reduced magnetic braking in polars from binary population models

“…As we generate both single stars and binaries, we can normalize the results of our population synthesis such that the number of single WDs corresponds to a specific birth rate of WDs in the Galactic disc. We adopt a WD space density of ∼ 5 × 10 −3 pc −3 (Holberg et al 2008(Holberg et al , 2016Jiménez-Esteban et al 2018;Hollands et al 2018) and a WD birth rate of ∼ 10 −12 pc −3 yr −1 (Vennes et al 1997;Holberg et al 2016), which implies a WD formation rate of ∼ 0.4 yr −1 , and provides a total number of ∼ 4 × 10 9 WDs in the disc. In order to derive the absolute number of systems that should be present in the Galactic disc, we similarly scaled the total number of CVs.…”

Gravitational waves from fast-spinning white dwarfs

“…Besides their high magnetic fields, most of them have been shown to be massive, and responsible for the high-mass peak at 1 M of the WD mass distribution; for instance: REJ 0317-853 has M ≈ 1.35 M and B ≈ (1.7-6.6) × 10 8 G ( Barstow et al 1995;Külebi et al 2010); PG 1658+441 has M ≈ 1.31 M and B ≈ 2.3 × 10 6 G (Liebert et al 1983;Schmidt et al 1992); and PG 1031+234 has the highest magnetic field B ≈ 10 9 G (Schmidt et al 1986;Külebi et al 2009). The existence of ultra-massive WDs has been revealed in several studies (see e.g., Castanheira et al 2013;Hermes et al 2013;Curd et al 2017;Camisassa et al 2019;Gentile Fusillo et al 2018;Jiménez-Esteban et al 2018).…”