Post common envelope binary

HD 101584 is a suspected post-common envelope binary. The engulfed companion triggered an outflow of gas, creating the nebula seen by ALMA.
Key stages in a common envelope phase. Top: A star fills its Roche lobe. Middle: The companion is engulfed; the core and companion spiral towards one another inside a common envelope. Bottom: The envelope is ejected and forms a PCEB or the two stars merge.

A post-common envelope binary (PCEB) 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.[1] 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.[2] Even more rare are PCEBs with a brown dwarf as the secondary.[1] A brown dwarf with a mass lower than 20 MJ might evaporate during the common envelope phase and therefore the secondary is supposed to have a mass higher than 20 MJ.[3]

The material ejected from the common envelope forms a planetary nebula. 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.[4]

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.[5]

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 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.[6]

  1. ^ a b Casewell, S. L.; Braker, I. P.; Parsons, S. G.; Hermes, J. J.; Burleigh, M. R.; Belardi, C.; Chaushev, A.; Finch, N. L.; Roy, M.; Littlefair, S. P.; Goad, M. (2018-05-01). "The first sub-70 minute non-interacting WD-BD system: EPIC212235321". Monthly Notices of the Royal Astronomical Society. 476 (1): 1405–1411. arXiv:1801.07773. Bibcode:2018MNRAS.476.1405C. doi:10.1093/mnras/sty245. ISSN 0035-8711. S2CID 55776991.
  2. ^ Muirhead, Philip S.; Vanderburg, Andrew; Shporer, Avi; Becker, Juliette; Swift, Jonathan J.; Lloyd, James P.; Fuller, Jim; Zhao, Ming; Hinkley, Sasha; Pineda, J. Sebastian; Bottom, Michael (2013-04-02). "Characterizing the Cool KOIs. V. KOI-256: A Mutually Eclipsing Post-Common Envelope Binary". The Astrophysical Journal. 767 (2): 111. arXiv:1304.1165. Bibcode:2013ApJ...767..111M. doi:10.1088/0004-637X/767/2/111. ISSN 0004-637X. S2CID 30368826.
  3. ^ "A Sub-Stellar Jonah – Brown Dwarf Survives Being Swallowed". www.eso.org. Retrieved 2020-02-02.
  4. ^ De Marco, Orsola; Reichardt, T.; Iaconi, R.; Hillwig, T.; Jacoby, G. H.; Keller, D.; Izzard, R. G.; Nordhaus, J.; Blackman, E. G. (October 2017). "Post-common envelope PN, fundamental or irrelevant?". Proceedings of the International Astronomical Union. 323: 213–217. arXiv:1612.03515. Bibcode:2017IAUS..323..213D. doi:10.1017/S1743921317002149. ISSN 1743-9221. S2CID 119069917.
  5. ^ Cite error: The named reference Olofsson et al was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Pulley2022 was invoked but never defined (see the help page).