Article · Wikipedia archive · Last revised Jul 8, 2026

Omicron1 Centauri

Omicron1 Centauri is a yellow hypergiant star in the southern constellation of Centaurus. Its name is a Bayer designation that is Latinized from ο1 Centauri, and abbreviated Omicron1 Cen or ο1 Cen. It is approximately 9,400 light-years from Earth.

Last revised
Jul 8, 2026
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Wikipedia ↗
ο1 Centauri
Location of ο1 Cen (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Centaurus
Right ascension 11h 31m 46.07s1
Declination −59° 26′ 31.4″1
Apparent magnitude (V) +5.132
Characteristics
Evolutionary stage Yellow hypergiant
Spectral type G3_0-Ia3
B−V color index +1.082
Variable type SRd4
Astrometry
Radial velocity (Rv)−20.005 km/s
Proper motion (μ) RA: −4.491 mas/yr1
Dec.: +1.604 mas/yr1
Parallax (π)0.3254±0.0734 mas1
Distance9,390 ± 330 ly
(2,880±100 pc)6
Absolute magnitude (MV)−9.07
Details
Mass27±5.48 M☉
Radius403±416 R☉
Luminosity210,000+88,000
−82,0006 L☉
Surface gravity (log g)0.199 cgs
Temperature5,70010 K
Age10–1210 Myr
Other designations
ο1 Cen, AAVSO 1127-58, CD−58°4100, GC 15818, HD 100261, HIP 56243, HR 4441, SAO 239145, CCDM J11318-592711
Database references
SIMBADdata

Omicron1 Centauri is a yellow hypergiant star in the southern constellation of Centaurus. Its name is a Bayer designation that is Latinized from ο1 Centauri, and abbreviated Omicron1 Cen or ο1 Cen. It is approximately 9,400 light-years from Earth.

A light curve for Omicron1 Centauri, adapted from O'Connell (1961)12 source ↗

ο1 Centauri is a yellow G-type supergiant or hypergiant with a mean apparent magnitude of +5.13. Daniel Joseph Kelly O'Connell discovered that the star is a variable star by studying photographic plates taken from 1934 to 1952, and announced his discovery in 1961.13 It is classified as a semiregular variable star and its brightness varies from magnitude +5.8 to +6.6 with a period of 200 days.4 Other studies have reported only small brightness variations.1415 It has been assigned the spectral types F8 Ia016 and F7 Ia/ab,17 indicating an F-type hypergiant or F-type supergiant respectively, but this has been revised to G3_0 Ia in 1989, indicating that it is a G-type hypergiant,3 and has been listed as the spectral standard for this class.18 The star is around 400 times larger than the Sun and roughly 210,000 times more luminous.6

ο1 Cen forms a very close naked eye double star with ο2 Centauri, a hotter blue supergiant that may be physically associated. ο1 Cen also has an 11th magnitude companion only 13.5" distant,19 although it appears to be a foreground star unrelated to the other two.20

References

References

  1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. Malyuto, V.; Schmidt-Kaler, T. (1997). "Quantitative spectral classification based on photoelectric spectrum scanner measurements of F-K stars". Astronomy and Astrophysics. 325: 693. Bibcode:1997A&A...325..693M.
  3. Keenan, Philip C.; McNeil, Raymond C. (October 1989). "The Perkins Catalog of Revised MK Types for the Cooler Stars". The Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373. ISSN 0067-0049.
  4. 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. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  5. Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
  6. Kasikov, A.; Mehner, A.; Kolka, I.; Aret, A. (2026-02-02). "Painting a Family Portrait of the Yellow Super- and Hypergiants in the Milky Way I. Constraining the Distances and Luminosities". Astronomy and Astrophysics. arXiv:2602.02449.
  7. Arellano Ferro, A.; et al. (1991). "A new discussion on the M(v) - W(O I 7774 A) relationship for F-G stars in the light of high-resolution data". Monthly Notices of the Royal Astronomical Society. 250: 1. Bibcode:1991MNRAS.250....1A. doi:10.1093/mnras/250.1.1.
  8. Kervella, Pierre; et al. (January 2022). "Stellar and substellar companions from Gaia EDR3. Proper-motion anomaly and resolved common proper-motion pairs". Astronomy and Astrophysics. 657: A7. arXiv:2109.10912. Bibcode:2022A&A...657A...7K. doi:10.1051/0004-6361/202142146. ISSN 0004-6361.
  9. Mallik, Sushma V. (1998). "The central depth of the Ca II triplet lines as a discriminant of chromospheric activity in late type stars". Bulletin of the Astronomical Society of India. 26: 479. Bibcode:1998BASI...26..479M.
  10. Kaler, James B. "Omicron 1,2 Centauri". Stars. University of Illinois. Retrieved 2017-12-05.
  11. "omi01 Cen". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2025-12-23.
  12. O'Connell, D. J. K. (1961). "The semi-regular variable o1 Centauri". Ricerche Astronomiche. 6 (13): 353–359. Bibcode:1961RA......6..353O.
  13. O'Connell, D. J. K. (1961). "The semi-regular variable o1 Centauri". Ricerche Astronomiche. 6 (13): 353–359. Bibcode:1961RA......6..353O. Retrieved 14 December 2024.
  14. Friedrich, D.; Schoffel, E. (1971). "New Bright Southern Variable Stars". Information Bulletin on Variable Stars. 558: 1. Bibcode:1971IBVS..558....1F.
  15. Sterken, C.; et al. (1993). "Longterm Photometry of Variables at ESO - Part Two - the Second Data Catalogue 1986-1990". Astronomy and Astrophysics Supplement. 102: 79. Bibcode:1993A&AS..102...79S.
  16. Mantegazza, L. (1992). "Luminosities of yellow supergiants from near-infrared spectra - Calibration through Magellanic Cloud stars". Astronomy and Astrophysics. 265: 527. Bibcode:1992A&A...265..527M.
  17. Houk, N.; Cowley, A. P. (1975). University of Michigan Catalogue of two-dimensional spectral types for the HD stars. Volume I. Declinations -90_ to -53_ƒ0. Bibcode:1975mcts.book.....H.
  18. Garcia, B. (1989). "A list of MK standard stars". Bulletin d'Information du Centre de Données Stellaires. 36: 27. Bibcode:1989BICDS..36...27G.
  19. Mason, Brian D.; et al. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  20. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.