Editing Brown dwarf (section)

=== White dwarf–brown dwarf binaries ===
[[File:LSPM J0241+2553AB.jpg|thumb|[[LSPM J0241+2553AB]], a wide white dwarf(A)–brown dwarf(B) binary.]]
Brown dwarfs around [[white dwarf]]s are quite rare. [[GD 165|GD 165 B]], the prototype of the L dwarfs, is one such system.<ref>{{cite journal |last1=Farihi |first1=Jay |last2=Christopher |first2=Micol|date=October 2004 |title=A Possible Brown Dwarf Companion to the White Dwarf GD 1400 |journal=The Astronomical Journal |volume=128 |issue=4 |pages=1868 |arxiv=astro-ph/0407036 |doi=10.1086/423919 |issn=1538-3881 |bibcode=2004AJ....128.1868F |s2cid=119530628 }}</ref> Such systems can be useful in determining the age of the system and the mass of the brown dwarf. Other white dwarf-brown dwarf binaries are [[COCONUTS-1|COCONUTS-1 AB]] (7&nbsp;billion years old),<ref name=":3" /> and [[LSPM J0055+5948|LSPM J0055+5948 AB]] (10&nbsp;billion years old),<ref name=":12">{{cite journal |last1=Meisner |first1=Aaron M. |last2=Faherty |first2=Jacqueline K. |last3=Kirkpatrick |first3=J. Davy |last4=Schneider |first4=Adam C. |last5=Caselden |first5=Dan |last6=Gagné |first6=Jonathan |last7=Kuchner |first7=Marc J. |last8=Burgasser |first8=Adam J. |last9=Casewell |first9=Sarah L. |last10=Debes |first10=John H. |last11=Artigau |first11=Étienne |last12=Bardalez Gagliuffi |first12=Daniella C. |last13=Logsdon |first13=Sarah E. |last14=Kiman |first14=Rocio |last15=Allers |first15=Katelyn |date=2020-08-01 |title=Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project |journal=The Astrophysical Journal |volume=899 |issue=2 |pages=123 |doi=10.3847/1538-4357/aba633 |arxiv=2008.06396 |bibcode=2020ApJ...899..123M |s2cid=221135837 |issn=0004-637X |doi-access=free }}</ref> [[SDSS J22255+0016|SDSS J22255+0016 AB]] (2&nbsp;billion years old)<ref name=":13">{{cite journal |last1=French |first1=Jenni R. |last2=Casewell |first2=Sarah L. |last3=Dupuy |first3=Trent J. |last4=Debes |first4=John H. |last5=Manjavacas |first5=Elena |last6=Martin |first6=Emily C. |last7=Xu |first7=Siyi |date=2023-03-01 |title=Discovery of a resolved white dwarf–brown dwarf binary with a small projected separation: SDSS J222551.65+001637.7AB |journal=Monthly Notices of the Royal Astronomical Society |volume=519 |issue=4 |pages=5008–5016 |doi=10.1093/mnras/stac3807 |doi-access=free |arxiv=2301.02101 |bibcode=2023MNRAS.519.5008F |issn=0035-8711}}</ref> [[WD 0806−661|WD 0806−661 AB]] (1.5–2.7&nbsp;billion years old).<ref>{{cite journal |last1=Leggett |first1=S. K. |last2=Tremblin |first2=P. |last3=Esplin |first3=T. L. |last4=Luhman |first4=K. L. |last5=Morley |first5=Caroline V. |date=2017-06-01 |title=The Y-type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry, and Near-infrared Spectroscopy |journal=The Astrophysical Journal |volume=842 |issue=2 |pages=118 |doi=10.3847/1538-4357/aa6fb5 |arxiv=1704.03573 |bibcode=2017ApJ...842..118L |s2cid=119249195 |issn=0004-637X |doi-access=free }}</ref>

Systems with close, [[Tidal locking|tidally locked]] brown dwarfs orbiting around white dwarfs belong to the [[post common envelope binary|post common envelope binaries]] or PCEBs. Only eight confirmed PCEBs containing a white dwarf with a brown dwarf companion are known, including [[WD 0137−349|WD 0137-349]] AB. In the past history of these close white dwarf–brown dwarf binaries, the brown dwarf is engulfed by the star in the [[Red giant|red giant phase]]. Brown dwarfs with a mass lower than 20 [[Jupiter mass]]es would [[Photoevaporation|evaporate]] during the engulfment.<ref>{{cite press release |first1=Pierre |last1=Maxted |first2=Ralf |last2=Napiwotzki |first3=Paul |last3=Dobbie |first4=Matt |last4=Burleigh |url=https://www.eso.org/public/news/eso0628/ |title=A Sub-Stellar Jonah – Brown Dwarf Survives Being Swallowed |publisher=European Southern Observatory |access-date=2019-12-11 }}</ref><ref>{{cite journal |last1=Casewell |first1=Sarah L. |last2=Braker |first2=Ian P. |last3=Parsons |first3=Steven G. |last4=Hermes |first4=James J. |last5=Burleigh |first5=Matthew R. |last6=Belardi |first6=Claudia |last7=Chaushev |first7=Alexander |last8=Finch |first8=Nicolle L. |last9=Roy |first9=Mervyn |last10=Littlefair |first10=Stuart P. |last11=Goad |first11=Mike |last12=Dennihy |first12=Erik |date=31 January 2018 |title=The first sub-70 min non-interacting WD–BD system: EPIC212235321 |journal=Monthly Notices of the Royal Astronomical Society |volume=476 |issue=1 |pages=1405–1411 |doi=10.1093/mnras/sty245 |doi-access=free |issn=0035-8711 |bibcode=2018MNRAS.476.1405C |arxiv=1801.07773 |s2cid=55776991 }}</ref> The dearth of brown dwarfs orbiting close to white dwarfs can be compared with similar observations of brown dwarfs around main-sequence stars, described as the [[brown-dwarf desert]].<ref>{{cite journal |last1=Longstaff |first1=Emma S. |last2=Casewell |first2=Sarah L. |last3=Wynn |first3=Graham A. |last4=Maxted |first4=Pierre F. L. |last5=Helling |first5=Christiane |date=2017-10-21 |title=Emission lines in the atmosphere of the irradiated brown dwarf WD0137−349B |url=https://academic.oup.com/mnras/article/471/2/1728/3974054 |journal=Monthly Notices of the Royal Astronomical Society |volume=471 |issue=2 |pages=1728–1736 |arxiv=1707.05793 |doi=10.1093/mnras/stx1786 |doi-access=free |issn=0035-8711 |bibcode=2017MNRAS.471.1728L |s2cid=29792989 }}</ref><ref>{{cite journal |last1=Grether |first1=Daniel |last2=Lineweaver |first2=Charles H. |date=April 2006 |title=How Dry is the Brown Dwarf Desert? Quantifying the Relative Number of Planets, Brown Dwarfs, and Stellar Companions around Nearby Sun-like Stars |journal=The Astrophysical Journal |volume=640 |issue=2 |pages=1051–1062 |doi=10.1086/500161 |arxiv=astro-ph/0412356 |bibcode=2006ApJ...640.1051G |issn=0004-637X |doi-access=free }}</ref> The PCEB might evolve into a [[cataclysmic variable star]] (CV*) with the brown dwarf as the donor.<ref>{{cite journal |last1=Rappaport |first1=Saul A. |last2=Vanderburg |first2=Andrew |last3=Nelson |first3=Lorne |last4=Gary |first4=Bruce L. |last5=Kaye |first5=Thomas G. |last6=Kalomeni |first6=Belinda |last7=Howell |first7=Steve B. |last8=Thorstensen |first8=John R. |last9=Lachapelle |first9=François-René |last10=Lundy |first10=Matthew |last11=St-Antoine |first11=Jonathan |date=2017-10-11 |title=WD 1202-024: the shortest-period pre-cataclysmic variable |url=https://academic.oup.com/mnras/article/471/1/948/3892367 |journal=Monthly Notices of the Royal Astronomical Society |volume=471 |issue=1 |pages=948–961 |arxiv=1705.05863 |doi=10.1093/mnras/stx1611 |doi-access=free |issn=0035-8711 |bibcode=2017MNRAS.471..948R |s2cid=119349942 }}</ref> Simulations have shown that highly evolved CV* are mostly associated with substellar donors (up to 80%).<ref name=":15">{{cite journal |last1=Neustroev |first1=Vitaly V. |last2=Mäntynen |first2=Iikka |date=2023-08-01 |title=A brown dwarf donor and an optically thin accretion disc with a complex stream impact region in the period-bouncer candidate BW Sculptoris |journal=Monthly Notices of the Royal Astronomical Society |volume=523 |issue=4 |pages=6114–6137 |doi=10.1093/mnras/stad1730 |arxiv=2212.03264 |bibcode=2023MNRAS.523.6114N |issn=0035-8711|doi-access=free }}</ref> A type of CV*, called [[WZ Sagittae|WZ Sge]]-type [[dwarf nova]] often show donors with a mass near the borderline of low-mass stars and brown dwarfs.<ref>{{cite journal |last=Kato |first=Taichi |date=2015-12-01 |title=WZ Sge-type dwarf novae |journal=Publications of the Astronomical Society of Japan |volume=67 |issue=6 |pages=108 |doi=10.1093/pasj/psv077 |arxiv=1507.07659 |bibcode=2015PASJ...67..108K |issn=0004-6264|doi-access=free }}</ref> The binary [[BW Sculptoris]] is such a dwarf nova with a brown dwarf donor. This brown dwarf likely formed when a donor star lost enough mass to become a brown dwarf. The mass loss comes with a loss of the orbital period until it reaches a minimum of 70–80 minutes at which the period increases again. This gives this evolutionary stage the name [[period bouncer]].<ref name=":15" /> There could also exist brown dwarfs that merged with white dwarfs. The nova [[CK Vulpeculae]] might be a result of such a white dwarf–brown dwarf merger.<ref>{{cite web |first1=Nicolás |last1=Lira |first2=Charles E. |last2=Blue |first3=Calum |last3=Turner |first4=Masaaki |last4=Hiramatsu |url=https://www.almaobservatory.org/en/press-release/when-is-a-nova-not-a-nova-when-a-white-dwarf-and-a-brown-dwarf-collide/ |title=When Is a Nova Not a 'Nova'? When a White Dwarf and a Brown Dwarf Collide |website=ALMA Observatory |url-status=dead |archive-url=https://web.archive.org/web/20191022055806/https://www.almaobservatory.org/en/press-release/when-is-a-nova-not-a-nova-when-a-white-dwarf-and-a-brown-dwarf-collide/ |archive-date=2019-10-22 |access-date=2019-11-12 }}</ref><ref>{{cite journal |last1=Eyres |first1=Stewart P. S. |last2=Evans |first2=Aneurin |last3=Zijlstra |first3=Albert |last4=Avison |first4=Adam |last5=Gehrz |first5=Robert D. |last6=Hajduk |first6=Marcin|author7-link=Sumner Starrfield |last7=Starrfield |first7=Sumner |last8=Mohamed |first8=Shazrene |last9=Woodward |first9=Charles E. |last10=Wagner |first10=R. Mark |date=2018-12-21 |title=ALMA reveals the aftermath of a white dwarf–brown dwarf merger in CK Vulpeculae |url=https://academic.oup.com/mnras/article/481/4/4931/5107360 |journal=Monthly Notices of the Royal Astronomical Society |volume=481 |issue=4 |pages=4931–4939 |arxiv=1809.05849 |doi=10.1093/mnras/sty2554 |doi-access=free |bibcode=2018MNRAS.481.4931E |s2cid=119462149 |issn=0035-8711 }}</ref>