Gamma Aquarii

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

Location of γ Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 22h 21m 39.37542s[1]
Declination –01° 23′ 14.4031″[1]
Apparent magnitude (V) 3.849[2]
Spectral type A0 V[3]
U−B color index –0.092[2]
B−V color index –0.060[2]
Radial velocity (Rv) –15[4] km/s
Proper motion (μ) RA: +129.53[1] mas/yr
Dec.: +7.77[1] mas/yr
Parallax (π) 19.92 ± 1.04[1] mas
Distance 164 ± 9 ly
(50 ± 3 pc)
Surface gravity (log g) 4.0[5] cgs
Temperature 10,500[5] K
Metallicity [Fe/H] +0.30[5] dex
Rotational velocity (v sin i) 80[6] km/s
Other designations
Sadalachbia, Sadachbia, 48 Aquarii, ADS 15864, BD-02°5741, FK5 842, HD 212061, HIP 110395, HR 8518, SAO 146044.[7]
Database references

Gamma Aquarii (γ Aquarii, abbreviated Gamma Aqr, γ Aqr), also named Sadachbia,[8] is a binary star in the constellation of Aquarius. It has an apparent visual magnitude of 3.849,[2] making it one of the brighter members of the constellation. Based upon parallax measurements, this star is located at a distance of roughly 164 light-years (50 parsecs) from the Sun, with an error margin of 5%.[1] The star is a spectroscopic binary with a period of 58.1 days.


γ Aquarii (Latinised to Gamma Aquarii) is the system's Bayer designation.

It bore the traditional name Sadachbia, from an Arabic expression سعد الأخبية (sa‘d al-’axbiyah), meaning "luck of the homes (tents)". In Hindi it is also called Satabhishaj (a hundred physicians); it is called Sadhayam in Tamil. In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Aoul al Achbiya (أول ألأجبية - awwil al ahbiyah), which was translated into Latin as Prima Tabernaculorum, meaning the first of luck of the homes (tents).[9] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[10] to catalogue and standardize proper names for stars. The WGSN approved the name Sadachbia for this star on 21 August 2016, and it is now so entered in the IAU Catalog of Star Names.[8]

This star, along with Pi Aquarii (Seat), Zeta Aquarii (Sadaltager / Achr al Achbiya) and Eta Aquarii (Hydria), were al Aḣbiyah (الأخبية), "the Tent".[11][12][13]

In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of Gamma Aquarii, Zeta Aquarii, Eta Aquarii and Pi Aquarii.[14] Consequently, Gamma Aquarii itself is known as 墳墓二 (Fén Mù èr, English: the Second Star of Tomb).[15]


Gamma Aquarii is an A-type main sequence star with a stellar classification of A0 V,[3] around two and a half times more massive than the Sun.[16] It is a candidate Lambda Boötis star, suggesting it may have accreted low-metallicity circumstellar gas some time in the past.[17] It is spinning relatively rapidly with a projected rotational velocity of 80 km s−1.[6] This value gives a lower bound on the actual azimuthal velocity along the star's equator. The outer atmosphere of Gamma Aquarii is radiating energy at an effective temperature of 10,500 K,[5] which is nearly double the temperature at the surface of the Sun. This heat is what gives Gamma Aquarii the white-hot glow of an A-type star.[18]


  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 Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars, 8: 59, Bibcode:1984SAAOC...8...59C. 
  3. ^ a b Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819. 
  4. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W. 
  5. ^ a b c d Baschek, Bodo; Searle, Leonard (February 1969), "The Chemical Composition of the Lambda Bootis Stars", Astrophysical Journal, 155: 537, Bibcode:1969ApJ...155..537B, doi:10.1086/149890. 
  6. ^ a b Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, Bibcode:2007A&A...463..671R, arXiv:astro-ph/0610785Freely accessible, doi:10.1051/0004-6361:20065224. 
  7. ^ "gam Aqr -- Star in double system", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg. 
  8. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  9. ^ Knobel, E. B. (June 1895), "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket", Monthly Notices of the Royal Astronomical Society, 55: 429–438, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429. 
  10. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 
  11. ^ Davis Jr., G. A. (October 1944), "The Pronunciations, Derivations, and Meanings of a Selected List of Star Names", Popular Astronomy, 52 (3): 12, Bibcode:1944PA.....52....8D 
  12. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 52, ISBN 0-486-21079-0, retrieved 2010-12-12. 
  13. ^ γ Aqr as Aoul al Achbiya or Prima Tabernaculorum (the first of luck of the homes or tents), Pi Aquarii as Wasat al Achbiya or Media Tabernaculorum (the middle of luck of the homes or tents) and Zeta Aquarii as Achr al Achbiya or Postrema Tabernaculorum (the end of luck of the homes or tents). Eta Aquarii should be designated as al Achbiya consistently, but it was not designated as the Arabic name except the name Hydria (Greek) or Deli (Hebrew)
  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) 香港太空館 - 研究資源 - 亮星中英對照表 Archived August 18, 2010, at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.
  16. ^ David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146. Bibcode:2015ApJ...804..146D. arXiv:1501.03154Freely accessible. doi:10.1088/0004-637X/804/2/146.  Vizier catalog entry
  17. ^ King, J. R. (July 1994), "Accretion from Circumstellar Discs and the Lambda-Bootis Phenomenon", Monthly Notices of the Royal Astronomical Society, 269 (1): 209–217, Bibcode:1994MNRAS.269..209K, doi:10.1093/mnras/269.1.209. 
  18. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-10, retrieved 2012-01-16. 

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