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Omicron Aquarii

Topic: Astronomy

 From HandWiki - Reading time: 7 min

Short description: Variable B-type star in the constellation Aquarius
Omicron Aquarii
Location of ο Aquarii (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Aquarius[1]
Right ascension  22h 03m 18.844s[2]
Declination −02° 09′ 19.31″[2]
Apparent magnitude (V) +4.71[3]
Characteristics
Spectral type B7 IVe[4]
U−B color index −0.39[3]
B−V color index −0.11[3]
Variable type γ Cas[5]
Astrometry
Radial velocity (Rv)+11.0[6] km/s
Proper motion (μ) RA: +24.593[2] mas/yr
Dec.: −11.720[2] mas/yr
Parallax (π)6.9984 ± 0.1424[2] mas
Distance466 ± 9 ly
(143 ± 3 pc)
Absolute magnitude (MV)−0.89[1]
Details
Mass4.2[7] M☉
Radius4.0±0.3[7] R☉
Luminosity340[1] L☉
Surface gravity (log g)3.13[8] cgs
Temperature11,145±498[9] K
Metallicity [Fe/H]−0.16[1] dex
Rotational velocity (v sin i)211±26[9] km/s
Other designations
ο Aqr, 31 Aquarii, BD−02 5681, FK5 3765, HD 209409, HIP 108874, HR 8402, SAO 145837[10]
Database references
SIMBADdata

Omicron Aquarii is a variable star in the equatorial constellation of Aquarius. Its name is a Bayer designation that is Latinized from ο Aquarii, and abbreviated Omicron Aqr or ο Aqr. Visible to the naked eye, it has an apparent visual magnitude of +4.71.[3] Parallax measurements put it at a distance of roughly 466 light-years (143 parsecs) from Earth.[2] It is drifting further away with a radial velocity of +11 km/s.[6] The star is a candidate member of the Pisces-Eridanus stellar stream of co-moving stars.[11]

It has the traditional star name Kae Uh, from the Chinese 蓋屋 (Mandarin pronunciation Gài Wū).[12] In Chinese astronomy, 蓋屋 is the rooftop, an asterism consisting of ο Aquarii and 32 Aquarii.[13] Consequently, the Chinese name for ο Aquarii itself is 蓋屋一 (Gài Wū yī, English: the First Star of Roofing.)[14]

Properties

A light curve for Omicron Aquarii, plotted from TESS data[15]

The spectrum of Omicron Aquarii fits a stellar classification of B7 IVe;[4] 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 has 4.2 times the mass of the Sun and four[7] times the Sun's radius. It is radiating 340[1] times the luminosity of the Sun from its photosphere at an effective temperature of 11,145 K.[9] This is classified as a Gamma Cassiopeiae type[5] variable star and its brightness varies from magnitude +4.68 down to +4.89.[16] It is likely a single star, with no stellar companions.[17]

This star is spinning 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] This is creating an equatorial bulge with a radius of 6.8±1.0 R☉ compared to a polar radius of 6.0±0.8 R☉. As a result, the polar temperature 11,500±578 K; higher than the equator.[9]

The emission lines are being generated by a circumstellar disk of hot hydrogen gas.[18] This disk has been globally stable for at least twenty years, as of 2020.[7] It is inclined at an angle of 75°±3° to the plane of the sky. 90% of the hydrogen emission comes from within 9.5 stellar radii of the host star, and the disk has an estimated mass of ∼1.8×10−10 of the star's mass.[19]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  3. ↑ 3.0 3.1 3.2 3.3 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. 
  4. ↑ 4.0 4.1 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. 
  5. ↑ 5.0 5.1 "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.
  6. ↑ 6.0 6.1 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. 
  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. et al. (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 9.2 9.3 Turis-Gallo, D. et al. (March 2025), "Unveiling stellar spin: Determining inclination angles in Be stars", Astronomy & Astrophysics 695: id. A129, doi:10.1051/0004-6361/202452825, Bibcode: 2025A&A...695A.129T. 
  10. ↑ "omi Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=omi+Aqr. 
  11. ↑ 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. 
  12. ↑ 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. 
  13. ↑ (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.
  14. ↑ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 日
  15. ↑ 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. 
  16. ↑ Ruban, E. V. et al. (September 2006), "Spectrophotometric observations of variable stars", Astronomy Letters 32 (9): 604–607, doi:10.1134/S1063773706090052R, Bibcode: 2006AstL...32..604R. 
  17. ↑ Hutter, D. J. et al. (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. ↑ Meilland, A. et al. (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. 
  19. ↑ Sigut, T. A. A. et al. (December 2015), "The Circumstellar Disk of the Be Star o Aquarii as Constrained by Simultaneous Spectroscopy and Optical Interferometry", The Astrophysical Journal 814 (2): id. 159, doi:10.1088/0004-637X/814/2/159, Bibcode: 2015ApJ...814..159S. 



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