Editing Alpha Centauri (section)

=== Physical properties ===
[[File:ESO - Alpha Centauri in the HR-System (by).jpg|thumb|ESO - Alpha Centauri in the HR-System (by)]]
[[File:Relative sizes of the Alpha Centauri components and other objects (artist’s impression).tif|thumb|Relative sizes and colour of the Alpha Centauri A, B and C (Proxima) and other [[List of nearest stars and brown dwarfs|local stars]], incl. the Sun and Jupiter (artist’s impression)]]

[[Asteroseismology|Asteroseismic]] studies, [[chromospheric activity]], and stellar rotation ([[gyrochronology]]) are all consistent with the Alpha Centauri system being similar in age to, or slightly older than, the Sun.<ref name="Mam08">{{cite journal |first1=E.E. |last1=Mamajek |first2=L.A. |last2=Hillenbrand |author2-link= Lynne Hillenbrand |year=2008 |title=Improved age estimation for Solar-type dwarfs using activity-rotation diagnostics |journal=Astrophysical Journal |volume=687 |issue=2 |pages=1264–1293|arxiv=0807.1686|bibcode=2008ApJ...687.1264M |doi=10.1086/591785 |s2cid=27151456 }}</ref> Asteroseismic analyses that incorporate tight observational constraints on the stellar parameters for the Alpha Centauri stars have yielded age estimates of {{val|4.85|0.5}} Gyr,<ref name=Thevenin02>{{cite journal|last1=Thévenin |first1= F.|last2=Provost |first2= J. |last3=Morel |first3= P. |last4=Berthomieu |first4= G.|last5=Bouchy |first5= F. |last6=Carrier |first6= F. |year=2002 |title=Asteroseismology and calibration of alpha&nbsp;Cen binary system |journal=Astronomy & Astrophysics |volume=392 |page=L9 |arxiv=astro-ph/0206283 |bibcode=2002A&A...392L...9T |doi=10.1051/0004-6361:20021074 |s2cid=17293259}}</ref> {{val|5.0|0.5}} Gyr,<ref name="Bazot12">{{cite journal |last1=Bazot |first1= M. |last2=Bourguignon |first2= S. |last3=Christensen-Dalsgaard |first3= J. |year=2012 |title=A Bayesian approach to the modelling of {{nobr|alpha Cen A}} |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=427 |issue=3 |pages=1847–1866 |arxiv=1209.0222 |bibcode=2012MNRAS.427.1847B |doi=10.1111/j.1365-2966.2012.21818.x |doi-access= free |s2cid=118414505}}</ref> {{nobr|5.2 ± 1.9 Gyr,}}<ref name=Miglio05>{{cite journal |last1=Miglio |first1= A.|last2=Montalbán |first2= J.|year=2005|title=Constraining fundamental stellar parameters using seismology. Application to α Centauri AB |journal=Astronomy & Astrophysics |volume=441|issue=2|pages=615–629|arxiv=astro-ph/0505537 |bibcode=2005A&A...441..615M|doi=10.1051/0004-6361:20052988 |s2cid=119078808}}</ref> 6.4 Gyr,<ref name=Thoul03>{{cite journal |last1=Thoul |first1= A. |last2=Scuflaire |first2= R. |last3=Noels |first3= A. |last4=Vatovez |first4= B. |last5=Briquet |first5= M.|last6=Dupret |first6= M.-A. |last7=Montalban |first7= J.
|year=2003 |title=A new seismic analysis of alpha Centauri |journal=Astronomy & Astrophysics |volume=402 |pages=293–297 |arxiv=astro-ph/0303467 |bibcode=2003A&A...402..293T |doi=10.1051/0004-6361:20030244 |s2cid=15886763}}</ref> and {{val|6.52|0.3}} Gyr.<ref name=Eggenberger04>{{cite journal |last1=Eggenberger |first1= P. |last2=Charbonnel |first2= C. |last3=Talon |first3= S. |last4=Meynet |first4= G. |last5=Maeder |first5= A. |last6=Carrier |first6= F. |last7=Bourban |first7= G. |year=2004 |title=Analysis of {{nobr|α Centauri AB}} including seismic constraints |journal=Astronomy & Astrophysics |volume=417 |pages=235–246|arxiv=astro-ph/0401606|bibcode=2004A&A...417..235E |doi=10.1051/0004-6361:20034203|s2cid=119487043}}</ref> Age estimates for the stars based on chromospheric activity (Calcium H & K emission) yield {{nobr|4.4 ± 2.1 Gyr,}} whereas gyrochronology yields {{val|5.0|0.3}} Gyr.<ref name=Mam08/> [[Stellar evolution]] theory implies both stars are slightly older than the Sun at 5 to 6 billion years, as derived by their mass and spectral characteristics.<ref name=Matt93/><ref name=stellar-model-kim>{{cite journal|last=Kim |first= Y-C. |year=1999 |title=Standard stellar models; {{nobr|alpha Cen A and B}} |journal=Journal of the Korean Astronomical Society |volume=32 |issue=2 |page=119 |bibcode=1999JKAS...32..119K}}</ref>

From the [[orbital elements]], the total mass of Alpha Centauri AB is about {{Solar mass|2.0|link=y}}{{efn|
<math display="block">\begin{smallmatrix} \left( \frac{\ 11.2 + 35.6\ }{ 2 }\right)^3 \frac{ 1 }{~ 79.91^2\ } \approx 2.0 \end{smallmatrix} \qquad </math> – see formula in [[Standard gravitational parameter#Two bodies orbiting each other|standard gravitational parameter]] article.
}}
– or twice that of the Sun.<ref name=Aitken/> The average individual stellar masses are about {{Solar mass|1.08}} and {{Solar mass|0.91}}, respectively,<ref name=Akeson2021/> though slightly different masses have also been quoted in recent years, such as {{Solar mass|1.14}} and {{Solar mass|0.92}},<ref name=RECONS/> totaling {{Solar mass|2.06}}. Alpha Centauri A and B have [[absolute magnitude]]s of +4.38 and +5.71, respectively.

==== Alpha Centauri AB System ====
[[File:Best image of Alpha Centauri A and B.jpg|thumb| {{nobr|α Centauri A}} (left) is of the same [[stellar classification|stellar type]]&nbsp;G2 as the Sun, while {{nobr|α Centauri B}} (right) is a K1-type star.<ref>{{cite web|title=Best image of Alpha Centauri A and B |url=http://www.spacetelescope.org/images/potw1635a/|website=spacetelescope.org|access-date=29 August 2016}}</ref>|alt=Two white disks side by side, each with coloured fringes and prominent diffraction spikes]]
===== Alpha Centauri A =====
'''Alpha Centauri A''', also known as '''Rigil Kentaurus''', is the principal member, or primary, of the binary system. It is a solar-like [[main sequence|main-sequence]] star with a similar yellowish colour,<ref name="csiro">{{cite web |title=The colour of stars |date=21 December 2004 |website=Australia Telescope, Outreach and Education |publisher=Commonwealth Scientific and Industrial Research Organisation |url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html|access-date=16 January 2012|url-status=dead|archive-url=https://web.archive.org/web/20120222183238/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |archive-date=22 February 2012}}</ref> whose [[stellar classification]] is [[spectral type]] G2-V;<ref name=torres2006/> it is about 10% more massive than the Sun,<ref name="Thevenin02"/> with a radius about 22% larger.<ref name=kervella2017>{{cite journal |title=The radii and limb darkenings of α Centauri A and B. Interferometric measurements with VLTI/PIONIER |journal=Astronomy & Astrophysics |first1=P. |last1=Kervella |first2=L. |last2=Bigot |first3=A. |last3=Gallenne |first4=F. |last4=Thévenin |volume=597 |page=A137 |date=January 2017 |doi=10.1051/0004-6361/201629505 |bibcode=2017A&A...597A.137K
|arxiv=1610.06185 |s2cid=55597767}}</ref> When considered among the individual [[List of brightest stars|brightest stars]] in the night sky, it is the fourth-brightest at an apparent magnitude of +0.01,<ref name="ducati"/> being slightly fainter than [[Arcturus]] at an [[apparent magnitude]] of −0.05.

The type of [[magnetic activity]] on Alpha Centauri A is comparable to that of the Sun, showing [[stellar corona|coronal]] variability due to [[star spot]]s, as modulated by the rotation of the star. However, since 2005 the activity level has fallen into a deep minimum that might be similar to the Sun's historical [[Maunder Minimum]]. Alternatively, it may have a very long stellar activity cycle and is slowly recovering from a minimum phase.<ref name="Ayres2014">{{cite journal|title=The Ups and Downs of α Centauri|last1=Ayres|first1=Thomas R.|journal=The Astronomical Journal|arxiv=1401.0847|volume=147|issue=3|id=59
|page=12|date=March 2014|doi=10.1088/0004-6256/147/3/59|bibcode=2014AJ....147...59A|s2cid=117715969}}</ref>

===== Alpha Centauri B =====
{{hatnote group|
{{about-distinguish|α Centauri B, also known as Toliman|Beta Centauri{{!}}β Centauri|HD 102964{{!}}B Centauri|HD 129116{{!}}b Centauri|section=yes}}{{other uses|Toliman (disambiguation)}}
}}
'''Alpha Centauri B''', also known as '''Toliman''', is the secondary star of the binary system. It is a main-sequence star of spectral type K1-V, making it more an orange colour than Alpha Centauri A;<ref name="csiro"/> it has around 90% of the mass of the Sun and a 14% smaller diameter. Although it has a lower luminosity than A, Alpha Centauri B emits more energy in the [[X-ray]] band.<ref name="Xrays"/> Its [[light curve]] varies on a short time scale, and there has been at least one observed [[Flare star|flare]].<ref name="Xrays">{{cite journal|last1=Robrade|first1=J.|last2=Schmitt|first2=J. H. M. M.|last3=Favata|first3=F.
|year=2005|title=X-rays from α Centauri – The darkening of the solar twin|journal=Astronomy and Astrophysics|volume=442|issue=1|pages=315–321|bibcode=2005A&A...442..315R|doi=10.1051/0004-6361:20053314 |arxiv=astro-ph/0508260|s2cid=119120}}</ref> It is more magnetically active than Alpha Centauri A, showing a cycle of {{Val|8.2|0.2|u=yr}} compared to 11 years for the Sun, and has about half the minimum-to-peak variation in coronal luminosity of the Sun.<ref name="Ayres2014"/> This cycle was recently re-estimated based on more than 20 years of high-resolution spectroscopic observations of the CaIIH&K lines showing a cycle of {{Val|7.8|0.2|u=yr}}.<ref name="Cretignier2024">{{cite journal|last1=Cretignier|first1=M.|last2=Hara|first2=N.|last3=Pietrow|first3=A.G.M.|year=2024|title=Stellar surface information from the Ca II H&K lines - II. Defining better activity proxies|journal=Monthly Notices of the Royal Astronomical Society|volume=535|issue=1|pages=2562–2584|bibcode=2024MNRAS.535.2562C|doi= 
10.1093/mnras/stae2508 |doi-access=free |arxiv=astro-ph/0508260|s2cid=119120}}</ref> Alpha Centauri B has an apparent magnitude of +1.35, slightly dimmer than [[Mimosa (star)|Mimosa]].<ref name="IAU-LSN"/>

==== Alpha Centauri C ====
{{Main|Proxima Centauri}}

Alpha Centauri C, better known as Proxima Centauri, is a small main-sequence [[red dwarf]] of spectral class M6-Ve. It has an [[absolute magnitude]] of +15.60, over 20,000 times fainter than the Sun. Its mass is calculated to be {{Solar mass|{{val|0.1221}}}}.<ref name="KervellaThévenin2017">{{cite journal|last1=Kervella|first1=P.|last2=Thévenin|first2=F.|last3=Lovis|first3=C.|title=Proxima's orbit around α Centauri |journal=Astronomy & Astrophysics|volume=598|year=2017|pages=L7|issn=0004-6361|doi=10.1051/0004-6361/201629930|arxiv=1611.03495|bibcode=2017A&A...598L...7K|s2cid=50867264}}</ref> It is the closest star to the Sun but is too faint to be visible to the naked eye.<ref name=ESA>{{cite web |title=Proxima Centauri UV flux distribution |url=http://sdc.cab.inta-csic.es/ines/Ines_PCentre/Demos/Fluxdist/pcentauri.html |access-date=July 11, 2007 |publisher=[[ESA]]|work=The Astronomical Data Centre}}</ref>

<div style="overflow:auto;">[[File:Relative positions of Sun, Alpha Centauri AB and Proxima Centauri.png|thumb|upright=5|center|Relative positions of Sun, Alpha Centauri AB and Proxima Centauri. Grey dot is projection of Proxima Centauri, located at the same distance as Alpha Centauri AB.|alt=Very wide rectangle with a dot labelled "Sun" on the left and two dots respectively labelled "Alpha Centauri AB" and "Proxima Centauri" on the right side, joined by lines labelled with distances and angles]]</div>