A post-common envelope binary (PCEB) or pre-cataclysmic variable is a

binary system A binary system is a system of two astronomical bodies of the same kind that are comparable in size. Definitions vary, but typically require the center of mass to be located outside of either object. (See animated examples.) The most common ki ...

consisting of a

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

or hot subdwarf and a

main-sequence star In astronomy, the main sequence is a classification of stars which appear on plots of stellar color versus brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of star ...

or a

brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...

. The star or brown dwarf shared a

common envelope In astronomy, a common envelope (CE) is gas that contains a binary star system. The gas does not rotate at the same rate as the embedded binary system. A system with such a configuration is said to be in a common envelope phase or undergoing comm ...

with the white dwarf progenitor in the

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

phase. In this scenario the star or brown dwarf loses

angular momentum Angular momentum (sometimes called moment of momentum or rotational momentum) is the rotational analog of Momentum, linear momentum. It is an important physical quantity because it is a Conservation law, conserved quantity – the total ang ...

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 wave Gravitational waves are oscillations of the gravitational field that Wave propagation, travel through space at the speed of light; they are generated by the relative motion of gravity, gravitating masses. They were proposed by Oliver Heaviside i ...

s and will eventually begin mass-transfer, resulting in a

cataclysmic variable In astronomy, cataclysmic variable stars (CVs) are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state. They were initially called novae (), since those with an outburst brightness visible to ...

. 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 Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. A high concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when hum ...

during the common envelope phase and therefore the secondary is supposed to have a mass higher than 20 . The material ejected from the common envelope forms a

planetary nebula A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to planets. The ...

. One in five planetary nebulae are 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 HD 101584 is a suspected Post common envelope binary, post-common envelope binary about 1,800 to 5,900 light-years distant in the constellation of Centaurus. The system is bright at optical wavelengths with an apparent visual magnitude of ...

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

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

s are often proposed as the cause 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 The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

References

{{Reflist, refs= {{Cite journal, last1=Olofsson, first1=H., last2=Khouri, first2=T., last3=Maercker, first3=M., last4=Bergman, first4=P., last5=Doan, first5=L., last6=Tafoya, first6=D., last7=Vlemmings, first7=W. H. T., last8=Humphreys, first8=E. M. L., last9=Lindqvist, first9=M., last10=Nyman, first10=L., last11=Ramstedt, first11=S., date=March 2019, title=HD 101584: circumstellar characteristics and evolutionary status, journal= Astronomy & Astrophysics, language=en, volume=623, pages=A153, doi=10.1051/0004-6361/201834897, arxiv=1902.02153, bibcode=2019A&A...623A.153O, s2cid=102480818, issn=0004-6361 {{cite journal , last1=Pulley , first1=D. , last2=Sharp , first2=I. D. , last3=Mallett , first3=J. , last4=von Harrach , first4=S. , date=August 2022 , title=Eclipse timing variations in post-common envelope binaries: Are they a reliable indicator of circumbinary companions? , journal=

Monthly Notices of the Royal Astronomical Society ''Monthly Notices of the Royal Astronomical Society'' (MNRAS) is a peer-reviewed scientific journal in astronomy, astrophysics and related fields. It publishes original research in two formats: papers (of any length) and letters (limited to ...

, volume=514 , issue=4 , pages=5725–5738 , doi=10.1093/mnras/stac1676 , doi-access=free , arxiv=2206.06919 , bibcode=2022MNRAS.514.5725P Binary stars White dwarfs Stellar phenomena

List of post-common envelope binaries

See also

References