Editing Alpha Centauri (section)

{{Short description|Star system in the Centaurus constellation}}
{{hatnote group|
{{About-distinguish|α Centauri, the multi-star system in the constellation Centaurus|HD 125823{{!}}a Centauri|HD 100673{{!}}A Centauri|Centaurus A}}
{{Other uses}}
}}
{{Use British English|date=November 2021}}
{{Use dmy dates|date=November 2021}}
{{Starbox begin
| name        = Alpha Centauri AB{{efn| [[Proxima Centauri]] is gravitationally bound to the {{nobr|α Centauri}} system, but for practical and historical reasons it is described in detail in its own article. }}
}}
{{Starbox image
| image       = [[File:Alpha, Beta and Proxima Centauri (1).jpg|300px|alt=Two bright stars against a dense background of fainter stars, with one of the fainter stars circled in red]]
| caption     = {{longitem|Alpha Centauri AB (left) forms a triple star system with [[Proxima Centauri]] (below, south of, {{nobr|α Centauri AB}}), circled in red. The bright star to the right is [[Beta Centauri]]. |style=font-size: 1em; padding: 4px 0;}} <!-- Please do not change. The two bright stars are Alpha and Beta, not just A and B. -->
}}
{{Starbox observe 2s
| epoch       = [[J2000.0]]
| constell    = [[Centaurus]]
| component1  = {{nobr|α Centauri A}} (Rigil Kentaurus)
| ra1         = {{RA|14|39|36.49400}}<ref name=hipparcos>{{cite journal |last1=Van Leeuwen |first1=F. |year=2007 |title=Validation of the new Hipparcos reduction |journal=Astronomy and Astrophysics |volume=474 |issue=2 |pages=653–664 |doi=10.1051/0004-6361:20078357 |arxiv=0708.1752 |bibcode=2007A&A...474..653V |s2cid=18759600}}</ref>
| dec1        = {{DEC|−60|50|02.3737}}<ref name=hipparcos/>
| appmag_v1   = +0.01<ref name=ducati>{{cite report |last1=Ducati |first1=J. R. |year=2002 |title=Catalogue of Stellar Photometry in Johnson's 11&nbsp;color system |series=CDS/ADC Collection of Electronic Catalogues |volume=2237 |department = VizieR Online Data Catalog |bibcode=2002yCat.2237....0D }}</ref>
| component2  = {{nobr|α Centauri B}} (Toliman)
| ra2         = {{RA|14|39|35.06311}}<ref name=hipparcos/>
| dec2        = {{DEC|−60|50|15.0992}}<ref name=hipparcos/>
| appmag_v2   = +1.33<ref name=ducati/>
}}
{{Starbox character
| engvar      = en-UK
| component   = A
| class       = G2V<ref name=torres2006>{{cite journal |last1=Torres |first1=C.A.O. |last2=Quast|first2=G.R. |last3=da Silva |first3=L. |last4=de la Reza |first4=R. |last5=Melo |first5=C.H.F. |last6=Sterzik |first6=M. |year=2006 |title=Search for associations containing young stars (SACY) |journal=[[Astronomy and Astrophysics]] |volume=460 |issue=3 |pages=695–708 |issn=0004-6361 |doi=10.1051/0004-6361:20065602 |arxiv=astro-ph/0609258 |bibcode=2006A&A...460..695T |s2cid=16080025}}</ref>
| b-v         = +0.71<ref name=ducati/>
| u-b         = 
| component2  = B
| class2      = K1V<ref name=torres2006/>
| b-v2        = +0.88<ref name=ducati/>
| u-b2        = 
}}
{{Starbox astrometry
| component1        = A
| radial_v          = {{val|−21.4|0.76}}<ref name=valenti2005>{{cite journal |last1=Valenti |first1=Jeff A. |last2=Fischer |first2=Debra A. |year=2005 |title=Spectroscopic properties of cool stars (SPOCS) I.&nbsp;1040 F, G, and K dwarfs from Keck, Lick, and AAT planet search programs |journal=The Astrophysical Journal Supplement Series |volume=159 |issue=1 |pages=141–166 |issn=0067-0049 |doi=10.1086/430500 |doi-access=free |bibcode=2005ApJS..159..141V }}</ref>
| prop_mo_ra        = −3679.25<ref name=hipparcos/>
| prop_mo_dec       = +473.67<ref name=hipparcos/>
| parallax          = 750.81
| p_error           = 0.38
| parallax_footnote = <ref name=Akeson2021>{{cite journal |last1=Akeson |first1=Rachel |last2=Beichman |first2=Charles |last3=Kervella |first3=Pierre |last4=Fomalont |first4=Edward |last5=Benedict |first5=G. Fritz |date=20 April 2021 |title=Precision millimeter astrometry of the {{nobr|α Centauri AB}} system |journal= [[The Astronomical Journal]] |volume=162 |issue=1 |page=14 |s2cid=233307418 |doi-access=free |doi=10.3847/1538-3881/abfaff |bibcode=2021AJ....162...14A |arxiv=2104.10086 }}</ref>
| absmag_v           = 4.38<ref name=Wiegert/>
| component2         = B
| radial_v2          = {{val|−18.6|1.64}}<ref name=valenti2005/>
| prop_mo_ra2        = −3614.39<ref name=hipparcos/>
| prop_mo_dec2       = +802.98<ref name=hipparcos/>
| parallax2          = 750.81
| p_error2           = 0.38
| parallax_footnote2 = <ref name=Akeson2021/>
| absmag_v2          = 5.71<ref name=Wiegert/>
}}
{{Starbox orbit
| primary       = A
| name          = B
| period        = {{val|79.762|0.019}}
| axis          = {{val|17.493|0.0096}}
| eccentricity  = {{val|0.51947|0.00015}}
| inclination   = {{val|79.243|0.0089}}
| node          = {{val|205.073|0.025}}
| periastron    = {{val|1875.66|0.012}}
| periarg       = {{val|231.519|0.027}}
| reference     = <ref name=Akeson2021/>
}}
{{Starbox detail
| component1           = {{nobr|α Centauri A}}
| mass                 = {{Val|1.0788|0.0029}}<ref name=Akeson2021/>
| radius               = {{Val|1.2175|0.0055}}<ref name=Akeson2021/>
| gravity              = 4.30<ref name=aaa449>{{cite journal |last1=Gilli |first1=G. |last2=Israelian |first2=G. |last3=Ecuvillon |first3=A. |last4=Santos |first4=N.C. |last5=Mayor |first5=M. |year=2006 |title=Abundances of refractory elements in the atmospheres of stars with extrasolar planets |journal=[[Astronomy and Astrophysics]] |volume=449 |issue=2 |pages=723–736 |id=libcode 2005astro.ph.12219G |doi=10.1051/0004-6361:20053850 |arxiv=astro-ph/0512219 |bibcode=2006A&A...449..723G |s2cid=13039037}}</ref>
| luminosity           = {{Val|1.5059|0.0019}}<ref name=Akeson2021/>
| temperature          = {{val|5804|13|fmt=commas}}<ref name="soubiran">{{Cite journal |last1=Soubiran |first1=C. |last2=Creevey |first2=O. L. |last3=Lagarde |first3=N. |last4=Brouillet |first4=N. |last5=Jofré |first5=P. |last6=Casamiquela |first6=L. |last7=Heiter |first7=U. |last8=Aguilera-Gómez |first8=C. |last9=Vitali |first9=S. |last10=Worley |first10=C. |last11=de Brito Silva |first11=D. |date=2024-02-01 |title=Gaia FGK benchmark stars: Fundamental Teff and log g of the third version |bibcode=2024A&A...682A.145S |journal=Astronomy and Astrophysics |volume=682 |pages=A145 |doi=10.1051/0004-6361/202347136 |arxiv=2310.11302 |issn=0004-6361}} [https://vizier.cds.unistra.fr/viz-bin/VizieR?-source=J/A%2BA/682/A145&Plx=%3E500 Alpha Centauri's database entry] at [[VizieR]].</ref>
| metal_fe             = {{val|0.20|0.01}}<ref name=soubiran/>
| rotational_velocity  = {{val|2.7|0.7}}<ref name=aaa470>{{cite journal |last1=Bazot |first1=M. |display-authors=etal |year=2007 |title=Asteroseismology of {{nobr|α Centauri A.}} Evidence of rotational splitting |journal=[[Astronomy and Astrophysics]] |volume=470 |issue=1 |pages=295–302 |doi=10.1051/0004-6361:20065694 |bibcode=2007A&A...470..295B |arxiv=0706.1682 |s2cid=118785894 }}</ref>
| rotation             =  {{val|28.3|0.5|ul=days}}<ref name=Huber2020>{{cite journal |last1=Huber |first1=Daniel |last2=Zwintz |first2=Konstanze |collaboration=the BRITE team  |date=July 2020 |title=Solar-like oscillations: Lessons learned & first results from TESS |journal=Stars and Their Variability Observed from Space |page=457 |bibcode=2020svos.conf..457H |arxiv=2007.02170 }}</ref>
| age_gyr              = >4.8
| component2           = {{nobr|α Centauri B}}
| mass2                = {{Val|0.9092|0.0025}}<ref name=Akeson2021/>
| radius2              = {{Val|0.8591|0.0036}}<ref name=Akeson2021/>
| gravity2             = 4.37<ref name=aaa449/>
| luminosity2          = {{Val|0.4981|0.0007}}<ref name=Akeson2021/>
| temperature2         = {{val|5207|12|fmt=commas}}<ref name=soubiran/>
| metal_fe2            = {{val|0.24|0.01}}<ref name=soubiran/>
| rotational_velocity2 = {{val|1.1|0.8}}<ref name=raassen2003>{{cite journal |last1=Raassen |first1=A.J.J. |last2=Ness |first2=J.-U. |last3=Mewe |first3=R. |last4=van der Meer |first4=R.L.J. |last5=Burwitz |first5=V. |last6=Kaastran |first6=J.S. |year=2003 |title=Chandra-LETGS X-ray observation of {{nobr|α Centauri:}} A nearby (G2V + K1V) binary system |journal=[[Astronomy & Astrophysics]] |volume=400 |issue=2 |pages=671–678 |bibcode=2003A&A...400..671R |doi=10.1051/0004-6361:20021899 |doi-access=free}}</ref>
| rotation2            = {{val|36.7|0.3|ul=days}}<!-- <ref name=dewarf2010>{{cite journal |last1=De Warf |first1=L. |last2=Datin |first2=K. |last3=Guinan |first3=E. |title=X-ray, FUV, and UV observations of {{nobr|α Centauri B:}} Determination of long-term magnetic activity cycle and rotation period |journal=[[The Astrophysical Journal]] |volume=722 |issue=1 |year=2010 |pages=343–357 |doi=10.1088/0004-637X/722/1/343 |arxiv=1009.1652 |bibcode=2010ApJ...722..343D |s2cid=118635144 }}</ref> --><ref name=Dumusque2014>{{cite journal |last1=Dumusque |first1=Xavier |date=December 2014 |title=Deriving Stellar Inclination of Slow Rotators Using Stellar Activity |journal=[[The Astrophysical Journal]] |volume=796 |issue=2 |pages=133 |doi=10.1088/0004-637X/796/2/133 |arxiv=1409.3593 |bibcode=2014ApJ...796..133D|s2cid=119184190 }}</ref>
| age_gyr2             = {{val|5.3|0.3}}<ref name=joyce>{{cite journal |last1=Joyce |first1=M. |last2=Chaboyer |first2=B. |year=2018 |title=Classically and asteroseismically constrained 1D stellar evolution models of {{nobr|α Centauri A}} and B using empirical mixing length calibrations |journal=[[The Astrophysical Journal]] |volume=864 |issue=1 |page=99 |arxiv=1806.07567 |bibcode=2018ApJ...864...99J |doi=10.3847/1538-4357/aad464 |doi-access=free |s2cid=119482849 }}</ref>
}}
{{Starbox catalog
 | names        = [[Gliese Catalogue of Nearby Stars|Gliese&nbsp;559]], [[Fifth Fundamental Catalogue|FK5&nbsp;538]], [[Cordoba Durchmusterung|CD]]−60°5483, [[Catalog of Components of Double and Multiple Stars|CCDM&nbsp;J14396-6050]], [[Boss General Catalogue|GC&nbsp;19728]]
 | component1   = α Cen A
 | names1       = Rigil&nbsp;Kentaurus, Rigil&nbsp;Kent, [[Bayer designation|α<sup>1</sup>&nbsp;Centauri]], [[Harvard Revised catalogue|HR&nbsp;5459]], [[Henry Draper catalogue|HD&nbsp;128620]], [[General Catalogue of Trigonometric Parallaxes|GCTP&nbsp;3309.00]], [[Luyten Half-Second catalogue|LHS&nbsp;50]], [[Smithsonian Astrophysical Observatory Star Catalog|SAO&nbsp;252838]], [[Hipparcos catalogue|HIP&nbsp;71683]]
 | component2   = α Cen B
 | names2       = Toliman, [[Bayer designation|α<sup>2</sup>&nbsp;Centauri]], [[Harvard Revised catalogue|HR&nbsp;5460]], [[Henry Draper catalogue|HD&nbsp;128621]], [[Luyten Half-Second catalogue|LHS 51]], [[Hipparcos catalogue|HIP&nbsp;71681]]
}}
{{Starbox reference
 | Simbad       = alpha+centauri|sn = AB
 | Simbad2      = TYC+9007-5849-1|sn2 = A
 | Simbad3      = TYC+9007-5848-1|sn3 = B
 | NSTED        = alf%20Cen
 | ARICNS       = 01151
}}
{{Starbox end}}

'''Alpha Centauri''' ('''{{nobr|α Centauri}}''', '''α&nbsp;Cen''', or '''Alpha Cen''') is a [[star system]] in the southern [[constellation]] of [[Centaurus (constellation)|Centaurus]]. It consists of three stars: Rigil Kentaurus ({{nobr|α Centauri A}}), Toliman ({{nobr|α Centauri B}}), and [[Proxima Centauri]] ({{nobr|α Centauri C}}).<ref name=WGSN/> Proxima Centauri is the [[List of nearest stars|closest star]] to the [[Sun]] at 4.2465&nbsp;[[light-year]]s (ly) which is 1.3020&nbsp;[[Parsec|pc]].

Rigil Kentaurus and Toliman are [[Sun-like]] stars ([[G-type main-sequence star|class&nbsp;G]] and [[K-type main-sequence star|K]], respectively) that together form the [[binary star]] system {{nobr|α Centauri AB}}. To the [[naked eye]], these two main components appear to be a single star with an [[apparent magnitude]] of −0.27. It is the brightest star in the constellation and the [[List of brightest stars|third-brightest]] in the [[night sky]], outshone by only [[Sirius]] and [[Canopus]].

Rigil Kentaurus has 1.1&nbsp;times the [[Solar mass|mass]] ({{solar mass}}) and 1.5&nbsp;times the [[Solar luminosity|luminosity of the Sun]] ({{solar luminosity}}), while Toliman is smaller and cooler, at {{solar mass|0.9}} and less than {{solar luminosity|0.5}}.<ref>{{cite press release |first1=Pierre |last1=Kervella |first2=Frederic |last2=Thevenin |date=15 March 2003 |title=A family portrait of the Alpha Centauri system |publisher=[[European Southern Observatory]] |page=5 |id=eso0307, PR 05/03 |bibcode=2003eso..pres...39. |url=http://www.eso.org/public/news/eso0307/ }}</ref> The pair orbit around a [[barycentre|common centre]] with an orbital period of 79&nbsp;years.<ref name=SixthCatOrbVisBin/> Their elliptical orbit is [[orbital eccentricity|eccentric]], so that the distance between A and B varies from 35.6&nbsp;[[astronomical unit]]s (AU), or about the distance between [[Pluto]] and the Sun, to {{nobr|11.2 AU,}} or about the distance between [[Saturn]] and the Sun. One astronomical unit is the distance from Earth to the Sun, 150 million kilometers.

[[Proxima Centauri]] is a small faint [[red dwarf]] ([[Stellar classification#Class M|class&nbsp;M]]). Though not visible to the naked eye, Proxima Centauri is the closest star to the Sun at a distance of {{cvt|1.30|pc|ly|2|order=flip}}, slightly closer than {{nobr|α Centauri AB}}. The distance between Proxima Centauri and {{nobr|α Centauri AB}} is about {{cvt|13000|AU|ly|2|lk=in}},<ref name=Kervella2017>{{cite journal |last1=Kervella |first1=P. |last2=Thévenin |first2=F. |last3=Lovis |first3=C. |date=January 2017 |title=Proxima's orbit around {{nobr|α Centauri}} |journal=Astronomy & Astrophysics |volume=598 |page=L7 |arxiv=1611.03495 |bibcode=2017A&A...598L...7K |doi=10.1051/0004-6361/201629930 |s2cid=50867264}}</ref> equivalent to about 430&nbsp;times the radius of [[Neptune|Neptune's]] orbit.

Proxima Centauri has one confirmed planet: [[Proxima Centauri b|Proxima&nbsp;b]], an [[Terrestrial planet|Earth-sized]] planet in the [[habitable zone]] (though it is unlikely to be habitable), one candidate planet, [[Proxima Centauri d|Proxima&nbsp;d]], [[sub-Earth]] which orbits very closely to the star,<ref name=Faria2022/> and the controversial [[Proxima Centauri c|Proxima&nbsp;c]], a [[mini-Neptune]] {{val|1.5}}&nbsp;[[astronomical unit]]s away.<ref name=Artigau2022/> Rigil Kentaurus may have a [[Candidate 1|Neptune-sized planet]] in the habitable zone, though it is not yet known with certainty to be planetary in nature and could be an artifact of the discovery mechanism.<ref name=WagnerBoehle2021/> Toliman has no known planets.<ref name=Rajpaul2016/>