Omicron Aquarii

Omicron Aquarii
Location of ο Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius[1]
Right ascension 22h 03m 18.844s[2]
Declination −02° 09′ 19.31″[2]
Apparent magnitude (V) +4.71[3]
Characteristics
Evolutionary stage main sequence[4]
Spectral type B5V[5]
U−B color index −0.39[3]
B−V color index −0.11[3]
Variable type γ Cas[6]
Astrometry
Radial velocity (Rv)+11.0[7] km/s
Proper motion (μ) RA: +24.593 mas/yr[2]
Dec.: −11.720 mas/yr[2]
Parallax (π)6.9984±0.1424 mas[2]
Distance466 ± 9 ly
(143 ± 3 pc)
Absolute magnitude (MV)−0.89[1]
Details
Mass4.2[8] M☉
Radius4.0±0.3[8] R☉
Luminosity644[9] L☉
Surface gravity (log g)3.51[9] cgs
Temperature11,145±498[10] K
Metallicity [Fe/H]−0.16[1] dex
Rotational velocity (v sin i)211±26[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 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.[7] The star is a candidate member of the Pisces-Eridanus stellar stream of co-moving stars.[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]

Properties

The spectrum of Omicron Aquarii fits a stellar classification of B5V, indicating that this is a main sequence star.[5]

Omicron Aquarii has 4.2 times the mass of the Sun and four[8] times the Sun's radius. It is radiating 644 times the luminosity of the Sun[9] from its photosphere at an effective temperature of 11,145 K.[10] This is classified as a Gamma Cassiopeiae type[6] variable star and its brightness varies from magnitude +4.68 down to +4.89.[17] It is likely a single star, with no stellar companions.[18]

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.[8] 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.[10]

The emission lines are being generated by a decreted circumstellar disk of hot hydrogen gas.[19] This disk has been globally stable for at least twenty years, as of 2020.[8] 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.[20]

References

  1. ^ a b c Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. XHIP record for this object at VizieR.
  2. ^ a b c d e 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.
  3. ^ 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.
  4. ^ Zorec, J.; Royer, F. (2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities". Astronomy and Astrophysics. 537: A120. arXiv:1201.2052. Bibcode:2012A&A...537A.120Z. doi:10.1051/0004-6361/201117691.
  5. ^ a b Arcos, C.; Kanaan, S.; Chávez, J.; Vanzi, L.; Araya, I.; Curé, M. (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. arXiv:1711.08675. Bibcode:2018MNRAS.474.5287A. doi:10.1093/mnras/stx3075.
  6. ^ a b "omi Aqr", General Catalogue of Variable Stars, Sternberg Astronomical Institute, retrieved 2012-07-03. Note: type = GCAS.
  7. ^ a b 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, 35 (35), Astronomisches Rechen-Institut Heidelberg: 1, Bibcode:1999VeARI..35....1W.
  8. ^ a b c d e 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, arXiv:2002.09552, Bibcode:2020A&A...636A.110D, doi:10.1051/0004-6361/201936039, S2CID 211258993, A110.
  9. ^ a b c Zorec, J.; Frémat, Y.; Domiciano De Souza, A.; Royer, F.; Cidale, L.; Hubert, A.-M.; Semaan, T.; Martayan, C.; Cochetti, Y. R.; Arias, M. L.; Aidelman, Y.; Stee, P. (2016). "Critical study of the distribution of rotational velocities of be stars. I. Deconvolution methods, effects due to gravity darkening, macroturbulence, and binarity". Astronomy and Astrophysics. 595: A132. Bibcode:2016A&A...595A.132Z. doi:10.1051/0004-6361/201628760.
  10. ^ a b c d Turis-Gallo, D.; et al. (March 2025), "Unveiling stellar spin: Determining inclination angles in Be stars", Astronomy & Astrophysics, 695, id. A129, arXiv:2503.07754, Bibcode:2025A&A...695A.129T, doi:10.1051/0004-6361/202452825.
  11. ^ "omi Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-07-03.
  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, arXiv:1905.10588, Bibcode:2019AJ....158...77C, doi:10.3847/1538-3881/ab2899, S2CID 166228270, 77.
  13. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 53, ISBN 0-486-21079-0, retrieved 2010-12-12. {{citation}}: ISBN / Date incompatibility (help)
  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 Archived 2011-05-22 at the Wayback Machine
  16. ^ MAST: Barbara A. Mikulski Archive for Space Telescopes, Space Telescope Science Institute, retrieved 8 December 2021.
  17. ^ 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/S1063773706090052R, S2CID 121747360.
  18. ^ 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, arXiv:2109.06839, Bibcode:2021ApJS..257...69H, doi:10.3847/1538-4365/ac23cb, S2CID 237503492.
  19. ^ 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, arXiv:1111.2487, Bibcode:2012A&A...538A.110M, doi:10.1051/0004-6361/201117955, S2CID 64777633.
  20. ^ 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, arXiv:1510.01980, Bibcode:2015ApJ...814..159S, doi:10.1088/0004-637X/814/2/159.
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