The mass function of hydrogen-rich white dwarfs: robust observational evidence for a distinctive high-mass excess near 1 M_⊙

Abstract

The mass function of hydrogen-rich atmosphere white dwarfs has been frequently found to reveal a distinctive high-mass excess near 1 M ⊙ . However, a significant excess of massive white dwarfs has not been detected in the mass function of the largest white dwarf catalogue to date from the Sloan Digital Sky Survey. Hence, whether a high-mass excess exists or not has remained an open question. In this work we build the mass function of the latest catalogue of data release 10 SDSS hydrogenrich white dwarfs, including the cool and faint population (i.e. effective temperatures 6,000T eff 12,000 K, equivalent to 12 mag M bol 13 mag). We show that the high-mass excess is clearly present in our mass function, and that it disappears only if the hottest (brightest) white dwarfs (those with T eff 12,000 K, M bol 12 mag) are considered. This naturally explains why previous SDSS mass functions failed at detecting a significant excess of high-mass white dwarfs. Thus, our results provide additional and robust observational evidence for the existence of a distinctive highmass excess near 1 M ⊙ . We investigate possible origins of this feature and argue that the most plausible scenario that may lead to an observed excess of massive white dwarfs is the merger of the degenerate core of a giant star with a main sequence or a white dwarf companion during or shortly after a common envelope event.

A study of cool white dwarfs in the Sloan Digital Sky Survey Data Release 12

“…The cumulative distance distribution for our DA and non-DA samples follow a cubic rule up to 110 pc, indicating that our sample should be near complete up to this distance in the SDSS spectroscopic cone Holberg et al 2016). To ensure the reliability of our results we present our determinations for a close to complete sample corrected by the observed volume, following Schmidt (1968Schmidt ( , 1975; Green (1980); Stobie et al (1989); Liebert et al (2003); Kepler et al (2007); Limoges & Bergeron (2010); Rebassa-Mansergas et al (2015), limiting the magnitude on SDSS filter g, 14.5 < mg < 19.0, and assuming a galactic disk scale height of 300 pc. The resulting sample after applying the magnitude limits for the correction is composed of 5 336 DAs and 1 315 non-DAs.…”

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

“…Recently, Maoz et al (2018) claimed that up to a ∼10 per cent of the observed single white dwarfs are expected to be the result of binary white dwarf mergers, thus significantly contributing to the massive content of these objects. Alternatively, binary scenarios such as the merger of the degenerate core of a giant star with a main-sequence or a white dwarf companion (Rebassa-Mansergas et al 2015b) have also been proposed. Other possibilities, which are not a priori disposable, also exist.…”

Asteroseismic Signatures of Evolving Internal Stellar Magnetic Fields

“…Figure 3 shows that the core convective region is restricted to mass coordinates below ≈0.5 M e for stars of M  2.5 M e . Using the MS-WD mass relation of Renedo et al (2010) and Andrews et al (2015), these low-mass stars account for the majority of WDs, whose mass distribution peaks near 0.6 M e (Rebassa- Mansergas et al 2015). Since the ohmic diffusion time is very long in WDs (Ferrario et al 2015a), we expect that core-dynamo-generated fields are unlikely to be visible at the surface of most WDs.…”