Astronomy:Eta Centauri

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Short description: Star in the constellation Centaurus
Not to be confused with H Centauri.
Eta Centauri
Centaurus constellation map.svg
Red circle.svg
Location of η Centauri (circled)
Observation data
Equinox J2000.0]] (ICRS)
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])
Characteristics
Spectral type B1.5 Vne[4]
U−B color index −0.862[2]
B−V color index −0.215[2]
Variable type GCAS[3] + LERI
Astrometry
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
Distance306 ± 6 ly
(94 ± 2 pc)
Absolute magnitude (MV)−2.53[6]
Details
Mass12.0±0.3[7] M☉
Radius6.10±0.12[8] R☉
Luminosity8,700[4] L☉
Surface gravity (log g)3.95±0.04[8] cgs
Temperature25,700[4] K
Rotational velocity (v sin i)330[4] km/s
Age5.6±1.0[7] Myr
Other designations
η Cen, CD−41°8917, CPD−41°6839, FK5 537, HD 127972, HIP 71352, HR 5440, SAO 225044.[9]
Database references
SIMBADdata

Eta Centauri, Latinized from 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]

A light curve for Eta Centauri, plotted from TESS data[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 and the 'e' that it shows emission lines in its spectrum. It has a projected rotational velocity of 330 km s−1[4] and completes a full rotation in less than a day.

As a Be star,[11] it has variable emissions in its hydrogen spectral lines. This emission can be modelled by a decretion disk of gas that has been ejected from the star by its rapid rotation and now follows a near-Keplerian orbit around the central body.[12] Its brightness is also slightly variable, and it is 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 with variations caused by its rotation and pulsations.[13]

Eta Centauri has about 12 times the mass of the Sun,[7] 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 the luminosity of the Sun from its outer atmosphere at an effective temperature of 25,700 K.[4] At this temperature, the star glows 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.[15]

In traditional Chinese astronomy, Eta Centauri was known as 庫樓二[16] (meaning: the Second (Star) of Koo Low).[17]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V. 
  2. ↑ 2.0 2.1 2.2 2.3 Gutierrez-Moreno, Adelina; Moreno, Hugo (June 1968), "A photometric investigation of the Scorpio-Centaurus association", Astrophysical Journal Supplement Series 15: 459, doi:10.1086/190168, Bibcode: 1968ApJS...15..459G. 
  3. ↑ 3.0 3.1 3.2 Samus, N. N. 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. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 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, doi:10.1046/j.1365-8711.1999.02821.x, Bibcode: 1999MNRAS.309..221B. 
  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): 1, Bibcode: 1999VeARI..35....1W. 
  6. ↑ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A. 
  7. ↑ 7.0 7.1 7.2 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, doi:10.1111/j.1365-2966.2010.17434.x, Bibcode: 2011MNRAS.410..190T. 
  8. ↑ 8.0 8.1 Arcos, C. et al. (March 2018), "Stellar parameters and H α line profile variability of Be stars in the BeSOS survey", Monthly Notices of the Royal Astronomical Society 474 (4): 5287–5299, doi:10.1093/mnras/stx3075, Bibcode: 2018MNRAS.474.5287A. 
  9. ↑ "eta Cen". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=eta+Cen. 
  10. ↑ MAST: Barbara A. Mikulski Archive for Space Telescopes, Space Telescope Science Institute, https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html, retrieved 8 December 2021. 
  11. ↑ Janot-Pacheco; E.; Leister, N. V. et al. (1999), "Multi-periodicity of the Be star η Centauri from spectroscopic and photometric observations", Astronomy and Astrophysics Supplement Series 137 (3): 407, doi:10.1051/aas:1999256, Bibcode: 1999A&AS..137..407J. 
  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, doi:10.1088/0067-0049/187/1/228, Bibcode: 2010ApJS..187..228S. 
  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, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16. 
  15. ↑ 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. 
  16. ↑ (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.
  17. ↑ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York City , NY: Dover Publications Inc., p. 154, ISBN 0-486-21079-0. 

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