Post-common-envelope binary


A post-common-envelope binary or pre-cataclysmic variable is a binary system consisting of a white dwarf or hot subdwarf and a main-sequence star or a brown dwarf. The star or brown dwarf shared a common envelope with the white dwarf progenitor in the red-giant phase. In this scenario, the star or brown dwarf loses angular momentum as it orbits within the envelope, eventually leaving a main-sequence star and white dwarf in a short-period orbit. A PCEB will continue to lose angular momentum via magnetic braking and gravitational waves and will eventually begin mass transfer, resulting in a cataclysmic variable. While there are thousands of PCEBs known, there are only a few eclipsing PCEBs, also called ePCEBs. Even more rare are PCEBs with a brown dwarf as the secondary. A brown dwarf with a mass lower than 20 might evaporate during the common-envelope phase, so the secondary is supposed to have a mass higher than 20.
The material ejected from the common envelope forms a planetary nebula. One in five planetary nebulae are thought to be ejected from common envelopes, but this might be an underestimate. A planetary nebula formed by a common-envelope system usually shows a bipolar structure.
The suspected PCEB HD 101584 is surrounded by a complex nebula. During the common-envelope phase, the red-giant phase of the primary was terminated prematurely, avoiding a stellar merger. The remaining hydrogen envelope of HD 101584 was ejected during the interaction between the red giant and the companion, and it now forms the circumstellar medium around the binary.
Many eclipsing post-common-envelope binaries show variations in the timing of eclipses, the cause of which is uncertain. While orbiting exoplanets are often proposed as the causes of these variations, planetary models often fail to predict subsequent changes in eclipse timing. Other proposed causes, such as the Applegate mechanism, often cannot fully explain the observed eclipse timing variations either.

List of post-common envelope binaries

Sorted by increasing orbital period.
NamePeriodSecondaryNote
SDSS J1205-024271.2 minuteslow-mass star or brown dwarfshortest period PCEB
WD 0137−349116 minutesbrown dwarffirst confirmed PCEB with a brown dwarf as a companion
CSS21055121.73 minutesbrown dwarfeclipsing binary
SDSS 15572.27 hoursbrown dwarfcircumbinary debris disk with a polluted white dwarf
V470 Camelopardalis
red dwarfeclipsing binary
NY Virginisred dwarfeclipsing binary
NSVS 14256825red dwarfeclipsing binary
HW Virginisred dwarfeclipsing binary
NN Serpentis3.12 hoursred dwarfeclipsing binary
WD 0837+1854.2 hoursbrown dwarfextreme mass ratio of the progenitor, with the primary having a mass of 3.5-3.7 and the secondary 25-30
RR Caelired dwarfeclipsing binary
DE Canum Venaticorumred dwarfeclipsing binary
central source of Hen 2-1114.616 hoursK-type main sequence starplanetary nebula and eclipsing binary
K 1-216.2192 hoursplanetary nebula
central source of Fleming 11.1953 dayswhite dwarfplanetary nebula
KOI-2561.37865 daysred dwarfeclipsing binary
central source of NGC 23921.9 dayshot white dwarfplanetary nebula and x-ray binary
central source of NGC 51894.04 daysmassive white dwarfplanetary nebula; primary is a low-mass Wolf-Rayet star
central source of NGC 234616 days>3.5 sub-giantplanetary nebula; one of the longest period PCEB which could host the most massive secondary
HD 101584150–200 daysred dwarf or white dwarfthe engulfment of the companion probably triggered gas to outflow, creating the nebula, seen with Hubble and ALMA; primary is a post-RGB star