Abstract
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, multithreaded 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.
Highlights
Binaries are important in many aspects of astrophysics such as their role as precursors of supernovae (Schaefer & Pagnotta 2012; Livio & Mazzali 2018), detectable sources of gravitational wave radiation (Nelemans 2018), and in the chemical evolution of galaxies (Tsujimoto et al 1995; De Donder & Vanbeveren 2004)
Once orbital angular momentum loss reduces the orbital separation of post-common envelope binaries (PCEBs) such that the main-sequence star fills its Roche lobe, mass transfer on to the white dwarf is initiated via the inner Lagrangian point between the two stars; the systems morph into Cataclysmic variables (CVs), with observational properties that radically differ from those of their detached progenitors
CVs are inherently easier to discover than PCEBs and double white dwarfs (DWDs)
Summary
Binaries are important in many aspects of astrophysics such as their role as precursors of supernovae (Schaefer & Pagnotta 2012; Livio & Mazzali 2018), detectable sources of gravitational wave radiation (Nelemans 2018), and in the chemical evolution of galaxies (Tsujimoto et al 1995; De Donder & Vanbeveren 2004). With the Gaia astrometry of 1.3 billion stars in hand, the limitation in extending the study of Pala et al (2020) to a larger volume and including all types of close white dwarf binaries, is the incompleteness of the known members of the different sub-classes. Pala et al (2020) estimated a 77 per cent completeness for the CVs within 150 pc; that value drops for larger distances and is poorly constrained for PCEBs. The first step within this project is to establish reference samples of each sub-type of white dwarf binaries that are as representative as possible. Diagram is the focus of this paper These reference samples will be used to define algorithms that identify white dwarf binary candidates, combining Gaia data with observations extending over a wider wavelength range. Gaia (Section 3), define the reference “Gold” samples for each subtype (Section 4) including a discussion of the selection effects that affect these samples, and use the Gold Samples to discuss the evolution of close white dwarf binaries in the Gaia HR diagram (Section 5)
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