Zeta Centauri
 Location of ζ Centauri (circled) |
|
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Centaurus |
| Right ascension | 13h 55m 32.38565s |
| Declination | −47° 17′ 18.1482″ |
| Apparent magnitude (V) | +2.55 |
| Characteristics | |
| Spectral type | B2.5 IV |
| U−B color index | −0.91 |
| B−V color index | −0.22 |
| Astrometry | |
| Radial velocity (Rv) | +6.5 km/s |
| Proper motion (μ) |
RA: −57.37 mas/yr Dec.: −44.55 mas/yr |
| Parallax (π) | 8.54 ± 0.13mas |
| Distance | 382 ± 6 ly (117 ± 2 pc) |
| Orbit | |
| Period (P) | 8.024 days |
| Semi-major axis (a) | 0.0014" |
| Eccentricity (e) | 0.5 |
| Periastron epoch (T) | 2413719.321 JD |
|
Argument of periastron (ω) (secondary) |
290° |
| Details | |
| Mass | 7.8 ± 0.1 M☉ |
| Radius | 5.80 ± 0.53 R☉ |
| Surface gravity (log g) | 3.84 ± 0.08 cgs |
| Temperature | 23,561 ± 283 K |
| Rotational velocity (v sin i) | 235 km/s |
| Age | 39.8 ± 5.7 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Zeta Centauri (ζ Centauri, ζ Cen) is a binary star system in the southern constellation of Centaurus. It has the proper name Alnair, from the scientific-ArabicNayyir Badan Qanṭūris (نير بطن قنطورس), meaning "The Bright (Star) of the Body of the Centaur". With a combined apparent visual magnitude of +2.55, 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.
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. Consequently, ζ Centauri itself is known as 庫樓一 (Kù Lóu yī, English: the First Star of Arsenal.)
ζ Cen is a double-lined spectroscopic binary system, 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. The estimated angular separation of the pair is 1.4 mas.
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