Towards a volumetric census of close white dwarf binaries – I. Reference samples

Abstract

Close white dwarf binaries play an important role across a range of astrophysics, including thermonuclear supernovae, the Galactic low-frequency gravitational wave signal, and the chemical evolution of the Galaxy. Progress in developing a detailed understanding of the complex, multi-threaded evolutionary pathways of these systems is limited by the lack of statistically sound observational constraints on the relative fractions of various sub-populations, and their physical properties. The available samples are small, heterogeneous, and subject to a multitude of observational biases. Our overarching goal is to establish a volume-limited sample of all types of white dwarf binaries that is representative of the underlying population as well as sufficiently large to serve as a benchmark for future binary population models. In this first paper, we provide an overview of the project, and assemble reference samples within a distance limit of 300 pc of known white dwarf binaries spanning the most common sub-classes: post-common envelope binaries containing a white dwarf plus a main sequence star, cataclysmic variables and double-degenerate binaries. We carefully vet the members of these “Gold” Samples, which span most of the evolutionary parameter space of close white dwarf binary evolution. We also explore the differences between magnitude and volume limited close white dwarf binary samples, and discuss how these systems evolve in their observational properties across the Gaia Hertzsprung-Russell diagram.

A catalogue of white dwarfs in Gaia EDR3

“…For the rest of the paper all mentions of white dwarfs refer only to this type of systems. Some white dwarfs with unresolved main sequence companions are also included by our initial selection, but the full parameter space spanned by this type of binaries is considerably larger (see figures 3, 6, 8 and 15 in Inight et al 2021) and a significant fraction of these systems cannot be identified using only Gaia data. Eqs.…”

“…The white dwarf luminosity function was also reexplored with unprecedented level of detail (Torres et al 2021); and Torres et al (2019) further investigated the memberships of white dwarfs into the thin disc, thick disc, and halo Galactic populations. Significant progress was also made for largescale identification and characterization of white dwarfs in binaries with main-sequence stars, either in common proper motion pairs (El-Badry, Rix & Weisz 2018), non-interacting unresolved systems (Inight et al 2021), or cataclysmic variables (Abril et al 2020;Pala et al 2020).…”

Eclipsing white dwarf binaries in Gaia and the Zwicky Transient Faaccility

“…Ho we ver, with the addition of Gaia and other auxiliary data it is possible to make some constraints or to rule out certain classes of sources (e.g. Gaia Collaboration et al 2019 ;Inight et al 2021 ). The 18 new binaries are shown on the Gaia H-R diagram in Fig.…”

TUVO-21acq: a new cataclysmic variable discovered through a UV outburst

“…In systems in which the WD has no magnetic field (or a very weak magnetic field), accretion occurs via an accretion disk that forms around the WD. If the WD has a moderate or strong magnetic field (at least 10 7 G; Zhilkin et al 2012;Inight et al 2021), the disk will be truncated or entirely prevented from forming, and matter will accrete through collimated streams infalling onto the magnetic poles of the WD (see e.g. Zhilkin et al 2012 for details of this process).…”