Pre-Cataclysmic Binaries

Abstract

Cataclysmic variables may be descended from initially wide binaries that underwent catastrophic loss of mass and angular momentum during a “common-envelope” phase. If this is the case, there should exist a class of detached “pre-cataclysmic” binaries: double nuclei of planetary nebulae, and close binaries containing hot subdwarfs or white dwarfs. The secondary stars should be lower-main-sequence objects, and the orbital periods should be short (<1.5 days).Ten such pre-cataclysmic binaries are now known (four central stars of planetary nebulae, two close binaries containing sd0B stars, and four containing white dwarfs). There are several observational hints that these systems lose angular momentum faster than provided by gravitational radiation, through magnetic braking driven by convective motions in the envelopes of the late-type secondaries.Numerous binaries exist that are very similar to pre-cataclysmic binaries but have periods longer than 1.5 days. This suggests that cataclysmic variables represent only the short-period tail of the distribution of objects that have emerged from common-envelope interaction.KeywordsOrbital PeriodLight CurveWhite DwarfCentral StarPlanetary NebulaThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.