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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
SIMBAD data

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]

References

  1. ^ a b c d e f van Leeuwen, F. (November 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
  2. ^ a b c d Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode: 1966CoLPL...4...99J
  3. ^ a b c d e f Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv: 1007.4883, Bibcode: 2011MNRAS.410..190T, doi: 10.1111/j.1365-2966.2010.17434.x, S2CID  118629873
  4. ^ a b Wilson, R. E. (1953), "General Catalogue of Stellar Radial Velocities", Carnegie Institute Washington D.C. Publication, Carnegie Institute of Washington D.C., Bibcode: 1953GCRV..C......0W
  5. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv: 1108.4971, Bibcode: 2012AstL...38..331A, doi: 10.1134/S1063773712050015, S2CID  119257644.
  6. ^ a b Maury, A. C. (1922), "The Orbit of the Spectroscopic Binary ζ Centauri", Harvard College Observatory Circular, 233: 1–4, Bibcode: 1922HarCi.233....1M
  7. ^ a b Halbwachs, J. L. (April 1981), "List of Estimated Angular Separations of Spectroscopic Binaries", Astronomy and Astrophysics Supplement, 44: 47, Bibcode: 1981A&AS...44...47H
  8. ^ a b c d Fitzpatrick, E. L.; Massa, D. (March 2005), "Determining the Physical Properties of the B Stars. II. Calibration of Synthetic Photometry", The Astronomical Journal, 129 (3): 1642–1662, arXiv: astro-ph/0412542, Bibcode: 2005AJ....129.1642F, doi: 10.1086/427855, S2CID  119512018
  9. ^ a b Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago, 239 (1): 1, Bibcode: 1970CoAsi.239....1B
  10. ^ "* zet Cen". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-03-01.
  11. ^ Kunitzsch, P.; Smart, T. (2006), A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd revised ed.), Cambridge, MA: Sky Pub, p. 4, ISBN  978-1-931559-44-7
  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. ^ van Rensbergen, W.; De Loore, C.; Jansen, K. (February 2006), "Evolution of interacting binaries with a B type primary at birth", Astronomy and Astrophysics, 446 (3): 1071–1079, Bibcode: 2006A&A...446.1071V, doi: 10.1051/0004-6361:20053543
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