White dwarfs in close binaries in the extreme ultraviolet explorer all-sky survey

Abstract

We examine the orbital and physical properties of the EUVE sample of white dwarfs found in binary systems with short orbital periods (∼ 1d). These systems, consisting of a hot white dwarf and a main sequence star, are recent survivors of a common envelope phase responsible for dramatic momentum losses and orbital shrinkage. The white dwarfs in close binaries also constitute a surprisingly large fraction of the total sample of white dwarfs discovered in the EUVE all-sky survey. Most secondary stars are M-dwarfs, with an average mass of > 0.5 M⊙, and comparisons with some simulated samples of close binaries suggest that many more systems with very low mass secondary stars (< 0.3 M⊙) remain to be discovered.