Zeta Centauri

Zeta Centauri
Location of ζ Centauri (circled)
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]
Distance382 ± 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
Mass7.8±0.1[3] M☉
Radius5.80±0.53[8] R☉
Surface gravity (log g)3.84±0.08[8] cgs
Temperature23561±283[8] K
Rotational velocity (v sin i)235[9] km/s
Age39.8±5.7[3] Myr
Other designations
Alnair, ζ Cen, CD−46 8949, CPD−46 6560, HD 121263, HIP 68002, HR 5231, SAO 224538[10]
Database references
SIMBADdata

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]

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]

  1. ^ a b c d e f Cite error: The named reference aaa474_2_653 was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference clpl4_99 was invoked but never defined (see the help page).
  3. ^ a b c d e f Cite error: The named reference mnras410_1_190 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference gcsrv was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference hcoc233 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference aas44_47 was invoked but never defined (see the help page).
  8. ^ a b c d Cite error: The named reference aj129_3_1642 was invoked but never defined (see the help page).
  9. ^ a b Cite error: The named reference csrv1970 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference kunitzsch_smart2006 was invoked but never defined (see the help page).
  12. ^ ibid., p.28.
  13. ^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  14. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 25 日
  15. ^ Cite error: The named reference aaa446_3_1071 was invoked but never defined (see the help page).