Alpha Centauri information

Alpha Centauri AB^{[note 1]}
	; Alpha Centauri AB (left) forms a triple star system with Proxima Centauri, circled in red. The bright star system to the right is Beta Centauri.
Observation data; Epoch J2000.0 Equinox J2000.0
Constellation	Centaurus
	Alpha Centauri A
Right ascension	14h 39m 36.49400s
Declination	−60° 50′ 02.3737″
Apparent magnitude (V)	+0.01
	Alpha Centauri B
Right ascension	14h 39m 35.06311s
Declination	−60° 50′ 15.0992″
Apparent magnitude (V)	+1.33
Characteristics
A
Spectral type	G2V
U−B color index	+0.24[citation needed]
B−V color index	+0.71
B
Spectral type	K1V
U−B color index	+0.68[citation needed]
B−V color index	+0.88
Astrometry
A
Radial velocity (Rv)	−21.4±0.76 km/s
Proper motion (μ)	RA: −3679.25 mas/yr ; Dec.: 473.67 mas/yr
Parallax (π)	750.81 ± 0.38 mas
Distance	4.344 ± 0.002 ly ; (1.3319 ± 0.0007 pc)
Absolute magnitude (MV)	4.38
B
Radial velocity (Rv)	−18.6±1.64 km/s
Proper motion (μ)	RA: −3614.39 mas/yr ; Dec.: +802.98 mas/yr
Parallax (π)	750.81 ± 0.38 mas
Distance	4.344 ± 0.002 ly ; (1.3319 ± 0.0007 pc)
Absolute magnitude (MV)	5.71
Orbit
Primary	A
Companion	B
Period (P)	79.762±0.019 yr
Semi-major axis (a)	17.493±0.0096″
Eccentricity (e)	0.51947±0.00015
Inclination (i)	79.243±0.0089°
Longitude of the node (Ω)	205.073±0.025°
Periastron epoch (T)	1875.66±0.012
Argument of periastron (ω); (secondary)	231.519±0.027°
Details
Alpha Centauri A
Mass	1.0788±0.0029 M☉
Radius	1.2175±0.0055 R☉
Luminosity	1.5059±0.0019 L☉
Surface gravity (log g)	4.30 cgs
Temperature	5,790[citation needed] K
Metallicity [Fe/H]	<0.20[citation needed] dex
Rotation	28.3±0.5 d
Rotational velocity (v sin i)	2.7±0.7 km/s
Age	4.85 Gyr
Alpha Centauri B
Mass	0.9092±0.0025 M☉
Radius	0.8591±0.0036 R☉
Luminosity	0.4981±0.0007 L☉
Surface gravity (log g)	4.37 cgs
Temperature	5,260[citation needed] K
Metallicity [Fe/H]	0.23[citation needed] dex
Rotation	36.7±0.3 d
Rotational velocity (v sin i)	1.1±0.8 km/s
Age	5.3±0.3 Gyr
Other designations
	Gliese 559, FK5 538, CD−60°5483, CCDM J14396-6050, GC 19728
	α Cen A: Rigil Kentaurus, Rigil Kent, α1 Centauri, HR 5459, HD 128620, GCTP 3309.00, LHS 50, SAO 252838, HIP 71683
	α Cen B: Toliman, α2 Centauri, HR 5460, HD 128621, LHS 51, HIP 71681
Database references
SIMBAD	AB
	A
	B
Exoplanet Archive	data
ARICNS	data

Alpha Centauri (α Centauri, Alpha Cen, or α Cen) is a triple star system in the southern constellation of Centaurus. It consists of three stars: Rigil Kentaurus (Alpha Centauri A), Toliman (B) and Proxima Centauri (C).^[13] Proxima Centauri is the closest star to the Sun at 4.2465 light-years (1.3020 pc).

Alpha Centauri A and B are Sun-like stars (Class G and K, respectively) that together form the binary star system Alpha 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 third-brightest in the night sky, outshone by only Sirius and Canopus.

Alpha Centauri A has 1.1 times the mass and 1.5 times the luminosity of the Sun, while Alpha Centauri B is smaller and cooler, at 0.9 solar mass and less than 0.5 solar luminosity.^[14] The pair orbit around a common centre with an orbital period of 79 years.^[15] Their elliptical orbit is eccentric, so that the distance between A and B varies from 35.6 astronomical units (AU), or about the distance between Pluto and the Sun, to 11.2 AU, or about the distance between Saturn and the Sun.

Alpha Centauri C, or Proxima Centauri, is a small faint red dwarf (Class M). Though not visible to the naked eye, Proxima Centauri is the closest star to the Sun at a distance of 4.24 ly (1.30 pc), slightly closer than Alpha Centauri AB. Currently, the distance between Proxima Centauri and Alpha Centauri AB is about 13,000 AU (0.21 ly),^[16] equivalent to about 430 times the radius of Neptune's orbit.

Proxima Centauri has two confirmed planets: Proxima b, an Earth-sized planet in the habitable zone discovered in 2016, and Proxima d, a candidate sub-Earth which orbits very closely to the star, announced in 2022.^[17] The existence of Proxima c, a mini-Neptune 1.5 AU away discovered in 2019, is controversial.^[18] Alpha Centauri A may have a 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.^[19] Alpha Centauri B has no known planets: planet Bb, purportedly discovered in 2012, was later disproven,^[20] and no other planet has yet been confirmed.

Cite error: There are <ref group=note> tags on this page, but the references will not show without a {{reflist|group=note}} template (see the help page).

^ ^a ^b ^c ^d ^e ^f Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
^ ^a ^b ^c ^d Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
^ ^a ^b Torres, C. A. O.; Quast, G. R.; da Silva, L.; de la Reza, R.; Melo, C. H. F.; Sterzik, M. (2006). "Search for associations containing young stars (SACY)". Astronomy and Astrophysics. 460 (3): 695–708. arXiv:astro-ph/0609258. Bibcode:2006A&A...460..695T. doi:10.1051/0004-6361:20065602. ISSN 0004-6361. S2CID 16080025.
^ ^a ^b Valenti, Jeff A.; Fischer, Debra A. (2005). "Spectroscopic Properties of Cool Stars (SPOCS) I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs". The Astrophysical Journal Supplement Series. 159 (1): 141–166. Bibcode:2005ApJS..159..141V. doi:10.1086/430500. ISSN 0067-0049.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Akeson, Rachel; Beichman, Charles; Kervella, Pierre; Fomalont, Edward; Benedict, G. Fritz (20 April 2021). "Precision Millimeter Astrometry of the α Centauri AB System". The Astronomical Journal. 162 (1): 14. arXiv:2104.10086. Bibcode:2021AJ....162...14A. doi:10.3847/1538-3881/abfaff. S2CID 233307418.
^ ^a ^b Cite error: The named reference Wiegert was invoked but never defined (see the help page).
^ ^a ^b Gilli G.; Israelian G.; Ecuvillon A.; Santos N. C.; Mayor M. (2006). "Abundances of Refractory Elements in the Atmospheres of Stars with Extrasolar Planets". Astronomy and Astrophysics. 449 (2): 723–736. arXiv:astro-ph/0512219. Bibcode:2006A&A...449..723G. doi:10.1051/0004-6361:20053850. S2CID 13039037. libcode 2005astro.ph.12219G.
^ Huber, Daniel; Zwintz, Konstanze; the BRITE team (July 2020). "Solar-Like Oscillations: Lessons Learned & First Results from TESS". Stars and Their Variability Observed from Space: 457. arXiv:2007.02170. Bibcode:2020svos.conf..457H.
^ Bazot, M.; et al. (2007). "Asteroseismology of α Centauri A. Evidence of rotational splitting". Astronomy and Astrophysics. 470 (1): 295–302. arXiv:0706.1682. Bibcode:2007A&A...470..295B. doi:10.1051/0004-6361:20065694. S2CID 118785894.
^ Dumusque, Xavier (December 2014). "Deriving Stellar Inclination of Slow Rotators Using Stellar Activity". The Astrophysical Journal. 796 (2): 133. arXiv:1409.3593. Bibcode:2014ApJ...796..133D. doi:10.1088/0004-637X/796/2/133. S2CID 119184190.
^ Raassen, A. J. J.; Ness, J.-U.; Mewe, R.; Van Der Meer, R. L. J.; Burwitz, V.; Kaastra, J. S. (2003). "Chandra-LETGS X-ray observation of α Centauri: A nearby (G2V + K1V) binary system". Astronomy & Astrophysics. 400 (2): 671–678. Bibcode:2003A&A...400..671R. doi:10.1051/0004-6361:20021899.
^ Joyce, M.; Chaboyer, B. (2018). "Classically and Asteroseismically Constrained 1D Stellar Evolution Models of α Centauri a and B Using Empirical Mixing Length Calibrations". The Astrophysical Journal. 864 (1): 99. arXiv:1806.07567. Bibcode:2018ApJ...864...99J. doi:10.3847/1538-4357/aad464. S2CID 119482849.
^ Cite error: The named reference WGSN was invoked but never defined (see the help page).
^ Kervella, Pierre; Thevenin, Frederic (15 March 2003). "A Family Portrait of the Alpha Centauri System". European Southern Observatory Press Release: 5. Bibcode:2003eso..pres...39. eso0307, PR 05/03.
^ Cite error: The named reference SixthCatOrbVisBin was invoked but never defined (see the help page).
^ Kervella, P.; Thévenin, F.; Lovis, C. (January 2017). "Proxima's orbit around α Centauri". Astronomy & Astrophysics. 598. L7. arXiv:1611.03495. Bibcode:2017A&A...598L...7K. doi:10.1051/0004-6361/201629930. S2CID 50867264.
^ Cite error: The named reference Faria2022 was invoked but never defined (see the help page).
^ Cite error: The named reference Artigau2022 was invoked but never defined (see the help page).
^ Cite error: The named reference WagnerBoehle2021 was invoked but never defined (see the help page).
^ Cite error: The named reference Rajpaul2016 was invoked but never defined (see the help page).

[hipparcos-2] ^ ^a ^b ^c ^d ^e ^f Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.

[ducati-3] Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.

[torres2006-4] Torres, C. A. O.; Quast, G. R.; da Silva, L.; de la Reza, R.; Melo, C. H. F.; Sterzik, M. (2006). "Search for associations containing young stars (SACY)". Astronomy and Astrophysics. 460 (3): 695–708. arXiv:astro-ph/0609258. Bibcode:2006A&A...460..695T. doi:10.1051/0004-6361:20065602. ISSN 0004-6361. S2CID 16080025.

[valenti2005-5] Valenti, Jeff A.; Fischer, Debra A. (2005). "Spectroscopic Properties of Cool Stars (SPOCS) I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs". The Astrophysical Journal Supplement Series. 159 (1): 141–166. Bibcode:2005ApJS..159..141V. doi:10.1086/430500. ISSN 0067-0049.

[Akeson2021-6] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Akeson, Rachel; Beichman, Charles; Kervella, Pierre; Fomalont, Edward; Benedict, G. Fritz (20 April 2021). "Precision Millimeter Astrometry of the α Centauri AB System". The Astronomical Journal. 162 (1): 14. arXiv:2104.10086. Bibcode:2021AJ....162...14A. doi:10.3847/1538-3881/abfaff. S2CID 233307418.

[Wiegert-7] Cite error: The named reference Wiegert was invoked but never defined (see the help page).

[aaa449-8] Gilli G.; Israelian G.; Ecuvillon A.; Santos N. C.; Mayor M. (2006). "Abundances of Refractory Elements in the Atmospheres of Stars with Extrasolar Planets". Astronomy and Astrophysics. 449 (2): 723–736. arXiv:astro-ph/0512219. Bibcode:2006A&A...449..723G. doi:10.1051/0004-6361:20053850. S2CID 13039037. libcode 2005astro.ph.12219G.

[Huber2020-9] Huber, Daniel; Zwintz, Konstanze; the BRITE team (July 2020). "Solar-Like Oscillations: Lessons Learned & First Results from TESS". Stars and Their Variability Observed from Space: 457. arXiv:2007.02170. Bibcode:2020svos.conf..457H.

[aaa470-10] Bazot, M.; et al. (2007). "Asteroseismology of α Centauri A. Evidence of rotational splitting". Astronomy and Astrophysics. 470 (1): 295–302. arXiv:0706.1682. Bibcode:2007A&A...470..295B. doi:10.1051/0004-6361:20065694. S2CID 118785894.

[Dumusque2014-11] Dumusque, Xavier (December 2014). "Deriving Stellar Inclination of Slow Rotators Using Stellar Activity". The Astrophysical Journal. 796 (2): 133. arXiv:1409.3593. Bibcode:2014ApJ...796..133D. doi:10.1088/0004-637X/796/2/133. S2CID 119184190.

[raassen2003-12] Raassen, A. J. J.; Ness, J.-U.; Mewe, R.; Van Der Meer, R. L. J.; Burwitz, V.; Kaastra, J. S. (2003). "Chandra-LETGS X-ray observation of α Centauri: A nearby (G2V + K1V) binary system". Astronomy & Astrophysics. 400 (2): 671–678. Bibcode:2003A&A...400..671R. doi:10.1051/0004-6361:20021899.

[joyce-13] Joyce, M.; Chaboyer, B. (2018). "Classically and Asteroseismically Constrained 1D Stellar Evolution Models of α Centauri a and B Using Empirical Mixing Length Calibrations". The Astrophysical Journal. 864 (1): 99. arXiv:1806.07567. Bibcode:2018ApJ...864...99J. doi:10.3847/1538-4357/aad464. S2CID 119482849.

[WGSN-14] Cite error: The named reference WGSN was invoked but never defined (see the help page).

[15] Kervella, Pierre; Thevenin, Frederic (15 March 2003). "A Family Portrait of the Alpha Centauri System". European Southern Observatory Press Release: 5. Bibcode:2003eso..pres...39. eso0307, PR 05/03.

[SixthCatOrbVisBin-16] Cite error: The named reference SixthCatOrbVisBin was invoked but never defined (see the help page).

[Kervella2017-17] Kervella, P.; Thévenin, F.; Lovis, C. (January 2017). "Proxima's orbit around α Centauri". Astronomy & Astrophysics. 598. L7. arXiv:1611.03495. Bibcode:2017A&A...598L...7K. doi:10.1051/0004-6361/201629930. S2CID 50867264.

[Faria2022-18] Cite error: The named reference Faria2022 was invoked but never defined (see the help page).

[Artigau2022-19] Cite error: The named reference Artigau2022 was invoked but never defined (see the help page).

[WagnerBoehle2021-20] Cite error: The named reference WagnerBoehle2021 was invoked but never defined (see the help page).

[Rajpaul2016-21] Cite error: The named reference Rajpaul2016 was invoked but never defined (see the help page).

Observation data Epoch J2000.0 Equinox J2000.0
Alpha Centauri AB (left) forms a triple star system with Proxima Centauri, circled in red. The bright star system to the right is Beta Centauri.
Constellation	Centaurus
Alpha Centauri A
Right ascension	14^h 39^m 36.49400^s^[1]
Declination	−60° 50′ 02.3737″
Apparent magnitude (V)	+0.01^[2]
Alpha Centauri B
Right ascension	14^h 39^m 35.06311^s^[1]
Declination	−60° 50′ 15.0992″
Apparent magnitude (V)	+1.33^[2]
Characteristics
A
Spectral type	G2V^[3]
U−B color index	+0.24^{[citation needed]}
B−V color index	+0.71^[2]
B
Spectral type	K1V^[3]
U−B color index	+0.68^{[citation needed]}
B−V color index	+0.88^[2]
Astrometry
A
Radial velocity (R_v)	−21.4±0.76 ^[4] km/s
Proper motion (μ)	RA: −3679.25^[1] mas/yr Dec.: 473.67^[1] mas/yr
Parallax (π)	750.81 ± 0.38 mas^[5]
Distance	4.344 ± 0.002 ly (1.3319 ± 0.0007 pc)
Absolute magnitude (M_V)	4.38^[6]
B
Radial velocity (R_v)	−18.6±1.64^[4] km/s
Proper motion (μ)	RA: −3614.39^[1] mas/yr Dec.: +802.98^[1] mas/yr
Parallax (π)	750.81 ± 0.38 mas^[5]
Distance	4.344 ± 0.002 ly (1.3319 ± 0.0007 pc)
Absolute magnitude (M_V)	5.71^[6]
Orbit^[5]
Primary	A
Companion	B
Period (P)	79.762±0.019 yr
Semi-major axis (a)	17.493±0.0096″
Eccentricity (e)	0.51947±0.00015
Inclination (i)	79.243±0.0089°
Longitude of the node (Ω)	205.073±0.025°
Periastron epoch (T)	1875.66±0.012
Argument of periastron (ω) (secondary)	231.519±0.027°
Details
Alpha Centauri A
Mass	1.0788±0.0029^[5] `M`_☉
Radius	1.2175±0.0055^[5] `R`_☉
Luminosity	1.5059±0.0019^[5] `L`_☉
Surface gravity (log g)	4.30^[7] cgs
Temperature	5,790^{[citation needed]} K
Metallicity [Fe/H]	<0.20^{[citation needed]} dex
Rotation	28.3±0.5 d^[8]
Rotational velocity (v sin i)	2.7±0.7^[9] km/s
Age	4.85 Gyr
Alpha Centauri B
Mass	0.9092±0.0025^[5] `M`_☉
Radius	0.8591±0.0036^[5] `R`_☉
Luminosity	0.4981±0.0007^[5] `L`_☉
Surface gravity (log g)	4.37^[7] cgs
Temperature	5,260^{[citation needed]} K
Metallicity [Fe/H]	0.23^{[citation needed]} dex
Rotation	36.7±0.3 d^[10]
Rotational velocity (v sin i)	1.1±0.8^[11] km/s
Age	5.3±0.3^[12] Gyr
Other designations
Gliese 559, FK5 538, CD−60°5483, CCDM J14396-6050, GC 19728
α Cen A: Rigil Kentaurus, Rigil Kent, α¹ Centauri, HR 5459, HD 128620, GCTP 3309.00, LHS 50, SAO 252838, HIP 71683
α Cen B: Toliman, α² Centauri, HR 5460, HD 128621, LHS 51, HIP 71681
Database references
SIMBAD	AB
	A
	B
Exoplanet Archive	data
ARICNS	data

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