Eta Centauri

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Eta Centauri
Centaurus constellation map.svg
Red circle.svg

Location of η Centauri (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Centaurus
Right ascension 14h 35m 30.42416s[1]
Declination −42° 09′ 28.1708″[1]
Apparent magnitude (V) +2.35[2] (2.30 - 2.41[3])
Spectral type B1.5 Vne[4]
U−B color index −0.862[2]
B−V color index −0.215[2]
Variable type γ Cassiopeiae[3]
Radial velocity (Rv) –0.2[5] km/s
Proper motion (μ) RA: −34.73[1] mas/yr
Dec.: −32.72[1] mas/yr
Parallax (π) 10.67 ± 0.21[1] mas
Distance 306 ± 6 ly
(94 ± 2 pc)
Mass 12.0 ± 0.3[6] M
Radius 5-6 R
Luminosity 8,700[4] L
Surface gravity (log g) 3.20[7] cgs
Temperature 25,700[4] K
Rotational velocity (v sin i) 330[4] km/s
Age 5.6 ± 1.0[6] Myr
Other designations
CD−41°8917, CPD−41°6839, FK5 537, HD 127972, HIP 71352, HR 5440, SAO 225044.[8]
Database references

Eta Centauri (η Cen, η Centauri) is a star in the southern constellation of Centaurus. It has an apparent visual magnitude of +2.35[2] and is located at a distance of around 306 light-years (94 parsecs).[1] In traditional Chinese astronomy, Eta Centauri was known as 庫樓二[9] (meaning: the Second (Star) of Koo Low).[10]

The stellar classification of this star is B1.5 Vne,[4] indicating that it is a B-type main sequence star. The 'n' suffix means that the absorption lines are broadened from rapid rotation. It has a projected rotational velocity of 330 km s−1[4] and completes a full rotation in less than a day. This is a Be star as shown by the 'e' suffix,[11] which means it has variable emissions in its hydrogen spectral lines. This emission can be modeled by a decretion disk of gas that has been ejected from the star and now follows a near Keplerian orbit around the central body.[12] Finally it is slightly variable, and classified as a Gamma Cassiopeiae variable star with multiple periods of variability.[3] The International Variable Star Index lists Eta Centauri as both a Gamma Cassiopeiae variable and a Lambda Eridani variable.[13]

Eta Centauri has about 12[6] times the mass of the Sun, placing it above the dividing line between stars that evolve into white dwarfs and those that turn into supernovae. It is radiating 8,700[4] times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 25,700 K.[4] This heat causes the star to glow with the blue-white hue common to B-type stars.[14] Eta Centauri is a proper motion member of the Upper-Centaurus Lupus sub-group in the Scorpius-Centaurus OB association, the nearest such co-moving association of massive stars to the Sun.[7]

See also[edit]


  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:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Gutierrez-Moreno, Adelina; Moreno, Hugo (June 1968), "A photometric investigation of the Scorpio-Centaurus association", Astrophysical Journal Supplement Series, 15: 459, Bibcode:1968ApJS...15..459G, doi:10.1086/190168 
  3. ^ a b c Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)". VizieR On-line Data Catalog: B/gcvs. 1: 02025. Bibcode:2009yCat....102025S. 
  4. ^ a b c d e f g h Balona, L. A.; Dziembowski, W. A. (October 1999), "Excitation and visibility of high-degree modes in stars", Monthly Notices of the Royal Astronomical Society, 309 (1): 221–232, Bibcode:1999MNRAS.309..221B, doi:10.1046/j.1365-8711.1999.02821.x 
  5. ^ Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, Astronomisches Rechen-Institut Heidelberg, 35 (35), Bibcode:1999VeARI..35....1W 
  6. ^ a b c 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:1007.4883Freely accessible, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x 
  7. ^ a b de Geus, E. J.; de Zeeuw, P. T.; Lub, J. (June 1989), "Physical parameters of stars in the Scorpio-Centaurus OB association", Astronomy and Astrophysics, 216 (1–2): 44–61, Bibcode:1989A&A...216...44D 
  8. ^ "eta Cen -- Be Star", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-03-03 
  9. ^ (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.
  10. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York, NY: Dover Publications Inc., p. 154, ISBN 0-486-21079-0 
  11. ^ Janot-Pacheco, E., Leister NV, et al. (1999), "Multi-periodicity of the Be star η Centauri from spectroscopic and photometric observations", Astronomy and Astrophysics Supplement Series, 137 (3): 407, Bibcode:1999A&AS..137..407J, doi:10.1051/aas:1999256 
  12. ^ Silaj, J.; Jones, C. E.; Tycner, C.; Sigut, T. A. A.; Smith, A. D. (March 2010), "A Systematic Study of Hα Profiles of Be Stars", Astrophysical Journal Supplement Series, 187 (1): 228–250, Bibcode:2010ApJS..187..228S, doi:10.1088/0067-0049/187/1/228 
  13. ^ Watson, C. L. (2006). "The International Variable Star Index (VSX)". The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23-25. 25: 47. Bibcode:2006SASS...25...47W. 
  14. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-10, retrieved 2012-01-16 

External links[edit]