Zeta Centauri, Latinized from ζ Centauri, is a binary star system in the southern constellation of Centaurus. It has the proper name Alnair /æˈnɛər/, from Arabic: نير بطن قنطورس, romanized: nayyir baṭan qanṭūris, lit. 'the bright (star) of the body of the centaur'.[11][12] With a combined apparent visual magnitude of +2.55,[2] it is one of the brighter members of the constellation. This system is close enough to the Earth that its distance can be measured directly using the parallax technique. This yields a value of roughly 382 light-years (117 parsecs), with a 1.6% margin of error.[1] It is drifting further away with a radial velocity of +6.5 km/s.[4]
Observation data Epoch J2000.0 Equinox J2000.0 | |
---|---|
Constellation | Centaurus |
Right ascension | 13h 55m 32.38565s[1] |
Declination | −47° 17′ 18.1482″[1] |
Apparent magnitude (V) | +2.55[2] |
Characteristics | |
Spectral type | B2.5 IV[3] |
U−B color index | −0.91[2] |
B−V color index | −0.22[2] |
Astrometry | |
Radial velocity (Rv) | +6.5[4] km/s |
Proper motion (μ) | RA: −57.37[1] mas/yr Dec.: −44.55[1] mas/yr |
Parallax (π) | 8.54 ± 0.13 mas[1] |
Distance | 382 ± 6 ly (117 ± 2 pc) |
Absolute magnitude (MV) | −2.79[5] |
Orbit[6] | |
Period (P) | 8.024 days |
Semi-major axis (a) | 0.0014"[7] |
Eccentricity (e) | 0.5 |
Periastron epoch (T) | 2413719.321 JD |
Argument of periastron (ω) (secondary) | 290° |
Details | |
Mass | 7.8±0.1[3] M☉ |
Radius | 5.80±0.53[8] R☉ |
Surface gravity (log g) | 3.84±0.08[8] cgs |
Temperature | 23561±283[8] K |
Rotational velocity (v sin i) | 235[9] km/s |
Age | 39.8±5.7[3] Myr |
Other designations | |
Database references | |
SIMBAD | data |
In Chinese, 庫樓 (Kù Lóu), meaning Arsenal, refers to an asterism consisting of ζ Centauri, η Centauri, θ Centauri, 2 Centauri, HD 117440, ξ1 Centauri, γ Centauri, τ Centauri, D Centauri and σ Centauri.[13] Consequently, the Chinese name for ζ Centauri itself is 庫樓一 (Kù Lóu yī, English: the First Star of Arsenal.)[14]
ζ Cen is a double-lined spectroscopic binary system,[15] which indicates that the orbital motion was detected by shifts in the absorption lines of their combined spectra caused by the Doppler effect. The two stars orbit each other over a period of slightly more than eight days with an orbital eccentricity of about 0.5.[6] The estimated angular separation of the pair is 1.4 mas.[7]
At an estimated age of 40 million years,[3] the primary component of this system appears to be in the subgiant stage of its evolution with a stellar classification of B2.5 IV.[3] It is a large star with nearly 8[3] times the mass of the Sun and close to 6[8] times the Sun's radius. This star is rotating rapidly with a projected rotational velocity of 235 km s−1.[9]