White dwarf–main-sequence binaries from Gaia EDR3: the unresolved 100 pc volume-limited sample

Abstract

We use the data provided by the Gaia Early Data Release 3 to search for a highly-complete volume-limited sample of unresolved binaries consisting of a white dwarf and a main sequence companion (i.e. WDMS binaries) within 100 pc. We select 112 objects based on their location within the Hertzsprung-Russell diagram, of which 97 are new identifications. We fit their spectral energy distributions (SED) with a two-body fitting algorithm implemented in VOSA (Virtual Observatory SED Analyser) to derive the effective temperatures, luminosities and radii (hence surface gravities and masses) of both components. The stellar parameters are compared to those from the currently largest catalogue of close WDMS binaries, from the Sloan Digital Sky Survey (SDSS). We find important differences between the properties of the Gaia and SDSS samples. In particular, the Gaia sample contains WDMS binaries with considerably cooler white dwarfs and main sequence companions (some expected to be brown dwarfs). The Gaia sample also shows an important population of systems consisting of cool and extremely low-mass white dwarfs, not present in the SDSS sample. Finally, using a Monte Carlo population synthesis code, we find that the volume-limited sample of systems identified here seems to be highly complete (≃ 80 ± 9 per cent), however it only represents ≃9 per cent of the total underlying population. The missing ≃91 per cent includes systems in which the main sequence companions entirely dominate the SEDs. We also estimate an upper limit to the total space density of close WDMS binaries of ≃ (3.7 ± 1.9) × 10−4 pc−3.

A population synthesis fitting of the Gaia resolved white dwarf binary population within 100 pc

“…5 as open symbols those objects with presumably helium-cores, founding 119 WDMS and 35 DWD of these systems, which represent 15% and 17% of its respective sub-population. These percentages are in agreement with other studies of the Gaia white dwarf population -see, for instance, (Rebassa-Mansergas et al 2021), where 46 low-mass objects have been found out of 235 WDMS (19%).…”

“…Note that this classification did not pretend to be exhaustive and rigorous, but just a rough classification. Note also that the sources classified as unresolved binaries are very likely to belong to the WDMS or cataclysmic variable types since these objects are located between the white dwarf and main sequence loci (Rebassa-Mansergas et al 2021).…”

“…That implies that the bolometric magnitude of the white dwarf should be brighter than its main-sequence counterpart. Otherwise, the binary object will be located outside this region, mainly on the main-sequence path of the HR-diagram (see Rebassa-Mansergas et al 2021) and, thus, not considered in our sample.…”

Characterising eclipsing white dwarf M dwarf binaries from multi-band eclipse photometry

“…This precision is, therefore, at or below the aim of 5 per cent precision which is necessary to discern systems with interesting subtypes of either component. Comparing these percentage uncertainties with the two other methods of characterisation mentioned -spectral decomposition (Rebassa-Mansergas et al 2012) and VOSA SED fitting (Rebassa-Mansergas et al 2021) -demonstrates that using the eclipse gives similar or better precision. For the WD mass, the median percentage uncertainty of the SDSS sample (Rebassa-Mansergas et al 3.…”

Characterisation of the eclipsing post-common-envelope binary TIC 60040774

“…Common-envelope evolution, in particular, also produces a significant population of close, but detached white-dwarf/main-sequence (WDMS) binaries. Rebassa-Mansergas et al (2021) recently estimated a WDMS space density of 3.7 × 10 −4 pc −3 , implying the presence of 1500 such systems within a distance of 100 pc. Approximately a quarter of WDMS are close enough that they must be post-commonenvelope binaries (PCEBs), and 10% of these PCEBs exhibit eclipses (Rebassa-Mansergas et al 2016;Parsons et al 2013Parsons et al , 2015.…”