![]() Alpha Centauri AB (left) forms a triple star system with Proxima Centauri (bottom to the α Centauri AB system), circled in red. The bright star system to the right is Beta Centauri. | |
Observation data Epoch J2000.0 Equinox J2000.0 | |
---|---|
Constellation | Centaurus |
α Centauri A | |
Right ascension | 14h 39m 36.49400s[1] |
Declination | −60° 50′ 02.3737″ |
Apparent magnitude (V) | +0.01[2] |
α Centauri B | |
Right ascension | 14h 39m 35.06311s[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 (Rv) | −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 (MV) | 4.38[6] |
B | |
Radial velocity (Rv) | −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 (MV) | 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 | |
α 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 | 5,891[8] K |
Metallicity [Fe/H] | 0.21[8] dex |
Rotation | 28.3±0.5 d[9] |
Rotational velocity (v sin i) | 2.7±0.7[10] km/s |
Age | 4.85 Gyr |
α 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 | 5,151[8] K |
Metallicity [Fe/H] | 0.12[8] dex |
Rotation | 36.7±0.3 d[11] |
Rotational velocity (v sin i) | 1.1±0.8[12] km/s |
Age | 5.3±0.3[13] Gyr |
Other designations | |
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, α Cen, or Alpha Cen) is a triple star system in the southern constellation of Centaurus. It consists of three stars: Rigil Kentaurus (α Centauri A), Toliman (α Centauri B), and Proxima Centauri (α Centauri C).[14] Proxima Centauri is the closest star to the Sun at 4.2465 light-years (1.3020 pc).
α Centauri A and B are Sun-like stars (class G and K, respectively) that together form the binary star system 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 third-brightest in the night sky, outshone by only Sirius and Canopus.
α Centauri A (Rigil Kentaurus) has 1.1 times the mass and 1.5 times the luminosity of the Sun, while α Centauri B (Toliman) is smaller and cooler, at 0.9 solar mass and less than 0.5 solar luminosity.[15] The pair orbit around a common centre with an orbital period of 79 years.[16] 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.
α Centauri C, or more commonly, 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 α Centauri AB. Currently, the distance between Proxima Centauri and α Centauri AB is about 13,000 AU (0.21 ly),[17] equivalent to about 430 times the radius of Neptune's orbit.
Proxima Centauri has two confirmed planets: Proxima b or α Centauri Cb, an Earth-sized planet in the habitable zone discovered in 2016, and Proxima d (α Centauri Cd), a candidate sub-Earth which orbits very closely to the star, announced in 2022.[18] The existence of Proxima c (α Centauri Cc), a mini-Neptune 1.5 AU away discovered in 2019, is controversial.[19] α 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.[20] α Centauri B has no known planets: Planet α Cen Bb, purportedly discovered in 2012, was later disproven,[21] and no other planet has yet been confirmed.
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