Omicron Aquarii

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Omicron Aquarii
Diagram showing star positions and boundaries of the Aquarius constellation and its surroundings
Cercle rouge 100%.svg

Location of ο Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 22h 03m 18.84403s[1]
Declination –02° 09′ 19.3067″[1]
Apparent magnitude (V) +4.71[2]
Spectral type B7 IVe[3]
U−B color index –0.39[2]
B−V color index –0.11[2]
Variable type γ Cas
Radial velocity (Rv) +11.0[4] km/s
Proper motion (μ) RA: +24.66[1] mas/yr
Dec.: –11.16[1] mas/yr
Parallax (π) 7.49 ± 0.23[1] mas
Distance 440 ± 10 ly
(134 ± 4 pc)
Radius 4.3[5] R
Surface gravity (log g) 3.13[6] cgs
Temperature 13,464 ± 164[5] K
Rotational velocity (v sin i) 282 ± 20[7] km/s
Other designations
31 Aquarii, BD–02 5681, FK5 3765, HD 209409, HIP 108874, HR 8402, SAO 145837.[8]
Database references

Omicron Aquarii (ο Aqr, ο Aquarii) is the Bayer designation for a star in the equatorial constellation of Aquarius. Visible to the naked eye, it has an apparent visual magnitude of +4.71.[2] Parallax measurements put it at a distance of roughly 440 light-years (130 parsecs) from Earth.[1]

In Chinese, 蓋屋 (Gài Wū), meaning Roofing, refers to an asterism consisting of ο Aquarii and 32 Aquarii.[9] Consequently, ο Aquarii itself is known as 蓋屋一 (Gài Wū yī, English: the First Star of Roofing.)[10]

The spectrum of Omicron Aquarii fits a stellar classification of B7 IVe;[3] the luminosity class of IV suggests that this is a subgiant star that is exhausting the supply of hydrogen at its core and is in the process of evolving into a giant star. The 'e' suffix on the class indicates that the spectrum shows emission lines of hydrogen, thus categorizing this as a Be star. Omicron Aquarii is rotating rapidly with a projected rotational velocity of 205 km/s.[11] The rotation rate along the equator may be as high as 77% of the critical rotation velocity, with the axis of rotation being inclined by around 70° ± 20°. The emission lines are being generated by a decreted circumstellar disk of hot hydrogen gas.[7]

It is classified as a Gamma Cassiopeiae type[12] variable star and its brightness varies from magnitude +4.68 to +4.89.[13]


  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, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Feinstein, A.; Marraco, H. G. (November 1979), "The photometric behavior of Be Stars", Astronomical Journal, 84: 1713–1725, Bibcode:1979AJ.....84.1713F, doi:10.1086/112600. 
  3. ^ a b Lesh, Janet Rountree (December 1968). "The Kinematics of the Gould Belt: an Expanding Group?". Astrophysical Journal Supplement. 17: 371. Bibcode:1968ApJS...17..371L. doi:10.1086/190179. 
  4. ^ Wielen, R.; et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W. 
  5. ^ a b Underhill, A. B.; et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society, 189: 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601. 
  6. ^ Soubiran, C.; Le Campion, J.-F.; Cayrel de Strobel, G.; Caillo, A. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, Bibcode:2010A&A...515A.111S, arXiv:1004.1069Freely accessible, doi:10.1051/0004-6361/201014247. 
  7. ^ a b Meilland, A.; Millour, F.; Kanaan, S.; Stee, Ph.; Petrov, R.; Hofmann, K.-H.; Natta, A.; Perraut, K. (February 2012), "First spectro-interferometric survey of Be stars. I. Observations and constraints on the disk geometry and kinematics", Astronomy & Astrophysics, 538: A110, Bibcode:2012A&A...538A.110M, arXiv:1111.2487Freely accessible, doi:10.1051/0004-6361/201117955. 
  8. ^ "omi Aqr -- Be Star", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-07-03. 
  9. ^ (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.
  10. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 日
  11. ^ Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590. 
  12. ^ "omi Aqr", General Catalogue of Variable Stars, Sternberg Astronomical Institute, retrieved 2012-07-03.  Note: type = GCAS.
  13. ^ Ruban, E. V.; et al. (September 2006), "Spectrophotometric observations of variable stars", Astronomy Letters, 32 (9): 604–607, Bibcode:2006AstL...32..604R, doi:10.1134/S1063773706090052. 

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