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

Abstract

ABSTRACT The Gaia mission has provided an unprecedented wealth of information about the white dwarf population of our Galaxy. In particular, our studies show that the sample up to 100 pc from the Sun can be considered as practically complete. This fact allows us to estimate a precise fraction of double-degenerate (1.18 ± 0.10 per cent) and white dwarf plus main-sequence stars (6.31 ± 0.23 per cent) among all white dwarfs through comoving pairs identification. With the aid of a detailed population synthesis code, we are able to reproduce synthetic white dwarf populations with nearly identical fractions as the observed ones, thus obtaining valuable information about the binary fraction, fb, initial mass ratio distribution, n(q), and initial separation distribution, f(a), among other parameters. Our best-fitting model is achieved within a 1σ confidence level for f(a) ∝ a−1, $n(q)\propto q^{n_q}$, with $n_q=-1.13^{+0.12}_{-0.10}$ and fb = 0.32 ± 0.02. The fraction of white dwarf mergers generated by this model is $9\sim 16{{\ \rm per\ cent}}$, depending on the common-envelope treatment. As sub-products of our modelling, we find that around $1\sim 3{{\ \rm per\ cent}}$ of the white dwarf population are unresolved double-degenerates and that only ${\sim}1{{\ \rm per\ cent}}$ of all white dwarfs contain a He-core. Finally, only a mild kick during white dwarf formation seems to be necessary for fitting the observed sky separation of double-degenerate systems.