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Omicron Aquarii

Topic: Astronomy

 From HandWiki - Reading time: 4 min
Short description: Variable B-type star in the constellation Aquarius
Omicron Aquarii
Aquarius IAU.svg
Red circle.svg
Location of ο Aquarii (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Aquarius
Right ascension  22h 03m 18.84403s[1]
Declination –02° 09′ 19.3067″[1]
Apparent magnitude (V) +4.71[2]
Characteristics
Spectral type B7 IVe[3]
U−B color index –0.39[2]
B−V color index –0.11[2]
Variable type γ Cas[4]
Astrometry
Radial velocity (Rv)+11.0[5] 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
Distance440 ± 10 ly
(134 ± 4 pc)
Absolute magnitude (MV)−0.89[6]
Details
Mass4.2[7] M☉
Radius4.0±0.3[7] R☉
Luminosity340[6] L☉
Surface gravity (log g)3.13[8] cgs
Temperature13,464±164[9] K
Metallicity [Fe/H]−0.16[6] dex
Rotational velocity (v sin i)282±20[10] km/s
Other designations
ο Aqr, 31 Aquarii, BD–02 5681, FK5 3765, HD 209409, HIP 108874, HR 8402, SAO 145837[11]
Database references
SIMBADdata

Omicron Aquarii, Latinized from ο Aquarii, is the Bayer designation for a variable 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] It is drifting further away with a radial velocity of +11 km/s.[5] The star is a candidate member of the Pisces-Eridanus stellar stream.[12]

It has the traditional star name Kae Uh, from the Chinese 蓋屋 (Mandarin pronunciation Gài Wū).[13] In Chinese astronomy, 蓋屋 is the rooftop, an asterism consisting of ο Aquarii and 32 Aquarii.[14] Consequently, the Chinese name for ο Aquarii itself is 蓋屋一 (Gài Wū yī, English: the First Star of Roofing.)[15]

A light curve for Omicron Aquarii, plotted from TESS data[16]

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. It is rotating rapidly with an equatorial rotational velocity of 368 km/s, which is ~96% of the star's critical rotation velocity of 391 km/s.[7] The emission lines are being generated by a decreted circumstellar disk of hot hydrogen gas.[10] This disk has been globally stable for at least twenty years, as of 2020.[7] It is likely a single star, with no stellar companions.[17]

Omicron Aquarii has 4.2 times the mass of the Sun, four[7] times the Sun's radius, and is radiating 340[6] times the luminosity of the Sun from its photosphere at an effective temperature of 13,464 K.[9] It is classified as a Gamma Cassiopeiae type[4] variable star and its brightness varies from magnitude +4.68 down to +4.89.[18]

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 Feinstein, A.; Marraco, H. G. (November 1979), "The photometric behavior of Be Stars", Astronomical Journal 84: 1713–1725, doi:10.1086/112600, Bibcode: 1979AJ.....84.1713F. 
  3. ↑ 3.0 3.1 Lesh, Janet Rountree (December 1968). "The Kinematics of the Gould Belt: an Expanding Group?". Astrophysical Journal Supplement 17: 371. doi:10.1086/190179. Bibcode: 1968ApJS...17..371L. 
  4. ↑ 4.0 4.1 "omi Aqr", General Catalogue of Variable Stars (Sternberg Astronomical Institute), http://www.sai.msu.su/gcvs/cgi-bin/ident.cgi?cat=HD++&num=209409, retrieved 2012-07-03.  Note: type = GCAS.
  5. ↑ 5.0 5.1 Wielen, R. et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg (Astronomisches Rechen-Institut Heidelberg) 35 (35): 1, Bibcode: 1999VeARI..35....1W. 
  6. ↑ 6.0 6.1 6.2 6.3 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 7.3 7.4 de Almeida, E. S. G. et al. (April 2020), "Visible and near-infrared spectro-interferometric analysis of the edge-on Be star o Aquarii", Astronomy & Astrophysics 636: 23, doi:10.1051/0004-6361/201936039, A110, Bibcode: 2020A&A...636A.110D 
  8. ↑ 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, doi:10.1051/0004-6361/201014247, Bibcode: 2010A&A...515A.111S. 
  9. ↑ 9.0 9.1 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 (3): 601–605, doi:10.1093/mnras/189.3.601, Bibcode: 1979MNRAS.189..601U. 
  10. ↑ 10.0 10.1 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, doi:10.1051/0004-6361/201117955, Bibcode: 2012A&A...538A.110M. 
  11. ↑ "omi Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=omi+Aqr. 
  12. ↑ Curtis, Jason L. et al. (August 2019), "TESS Reveals that the Nearby Pisces-Eridanus Stellar Stream is only 120 Myr Old", The Astronomical Journal 158 (2): 11, doi:10.3847/1538-3881/ab2899, 77, Bibcode: 2019AJ....158...77C. 
  13. ↑ Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 53, ISBN 0-486-21079-0, https://archive.org/details/starnamestheirlo00alle/page/53, retrieved 2010-12-12. 
  14. ↑ (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.
  15. ↑ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 日
  16. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html. 
  17. ↑ Hutter, D. J.; Tycner, C.; Zavala, R. T.; Benson, J. A.; Hummel, C. A.; Zirm, H. (2021). "Surveying the Bright Stars by Optical Interferometry. III. A Magnitude-limited Multiplicity Survey of Classical Be Stars". The Astrophysical Journal Supplement Series 257 (2): 69. doi:10.3847/1538-4365/ac23cb. Bibcode: 2021ApJS..257...69H. 
  18. ↑ Ruban, E. V. et al. (September 2006), "Spectrophotometric observations of variable stars", Astronomy Letters 32 (9): 604–607, doi:10.1134/S1063773706090052, Bibcode: 2006AstL...32..604R. 

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