Constraints on the pairing properties of main sequence stars from observations of white dwarfs in binary systems

TL;DR

This paper investigates the discrepancy between the high multiplicity rate of main sequence stars and the lower observed binary fraction of white dwarfs, proposing that many white dwarfs are hidden in double white dwarf or Sirius-like systems.

Contribution

It introduces the idea that many white dwarfs are in hidden binary systems, explaining the lower observed binary fraction compared to their main sequence progenitors.

Findings

White dwarfs are often in double white dwarf or Sirius-like systems.

Progenitors of white dwarf-M dwarf binaries follow Salpeter's IMF.

Pairing progenitors with secondary stars from the same IMF overpredicts observed systems.

Abstract

Observations of main sequence stars conducted over the last several decades have clearly shown that something like 50 per cent of stars of spectral types G and F occur in multiple systems. For earlier spectral types, the incidence of multiplicity is even higher. Thus, a volume limited sample of white dwarfs should reflect the percentage of binarity observed in stars of F to late B spectral types, which are their Main Sequence progenitors. However, a study of the local volume limited sample of white dwarfs (20 pc from the Sun) conducted by Holberg has shown that a white dwarf has a probability of only $\sim 32$ per cent of occurring in a binary system, in stark contrast to the observations of multiplicity of Main Sequence stars. Others studies have also led to the same conclusion. In this paper, we argue that the "hidden" white dwarfs are either in double white dwarf systems or in Sirius-like systems. We also show that the white dwarf progenitors of the SDSS white dwarf - M dwarf wide binaries are distributed according to Salpeter's IMF. However, they cannot be paired with secondary stars which are also drawn from this IMF, since such a pairing would produce a percentage of white dwarf-M dwarfs systems that is several times larger than observed.