Gamma Aquarii

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γ Aquarii
Aquarius constellation map.svg
Red circle.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
Distance164 ± 9 ly
(50 ± 3 pc)
Absolute magnitude (MV)+0.10[5]
Surface gravity (log g)4.0[6] cgs
Temperature10,500[6] K
Metallicity [Fe/H]+0.30[6] dex
Rotational velocity (v sin i)80[7] km/s
Other designations
Sadalachbia, Sadachbia, 48 Aquarii, ADS 15864, BD-02°5741, FK5 842, HD 212061, HIP 110395, HR 8518, SAO 146044, WDS J22217-0123A.[8]
Database references

Gamma Aquarii (γ Aquarii, abbreviated Gamma Aqr, γ Aqr) 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 taken during the Hipparcos mission, this star is located at a distance of approximately 164 light-years (50 parsecs) from the Sun.[1]

Gamma Aquarii is the primary or 'A' component of a double star designated WDS J22217-0123.[9] The secondary or 'B' component is UCAC2 31430071.[10] Gamma Aquarii A's two components are therefore designated WDS J22217-0123 Aa and Ab. Gamma Aquarii is traditionally also called Sadachbia /səˈdækbiə/,[11] a name now formally restricted to γ Aqr Aa.[12]


γ Aquarii (Latinised to Gamma Aquarii) is the system's Bayer designation. WDS J22217-0123 A is its designation in the Washington Double Star Catalog.

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).[13] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalogue and standardize proper names for stars. The WGSN approved the name Sadachbia for the component WDS J22217-0123 Aa on 21 August 2016, and it is now so included in the List of IAU-approved Star Names.[12]

This star, along with Pi Aquarii (Seat), Zeta Aquarii (Sadaltager / Achr al Achbiya) and Eta Aquarii (Hydria), were al Aḣbiyah الأخبية "the Tent".[15][16][17]

In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of Gamma Aquarii, Zeta Aquarii, Eta Aquarii and Pi Aquarii.[18] Consequently, the Chinese name for Gamma Aquarii itself is 墳墓二 (Fén Mù èr, English: the Second Star of Tomb).[19]


Gamma Aquarii is a spectroscopic binary with a period of 58.1 days.

It presents as 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.[20] It is a candidate Lambda Boötis star, suggesting it may have accreted low-metallicity circumstellar gas some time in the past.[21] It is spinning relatively rapidly with a projected rotational velocity of 80 km s−1.[7] 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,[6] 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.[22]


  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. arXiv:0708.1752. Bibcode:2007A&A...474..653V. 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. ^ Eggen, Olin J. (July 1998), "The Age Range of Hyades Stars", The Astronomical Journal, 116 (1): 284–292, Bibcode:1998AJ....116..284E, doi:10.1086/300413.
  6. ^ 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.
  7. ^ 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, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224.
  8. ^ "gam Aqr". SIMBAD. Centre de données astronomiques de Strasbourg.
  9. ^ "Washington Double Star Catalog". United States Naval Observatory. Retrieved 26 February 2018.
  10. ^ "UCAC2 31430071 -- Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2018-02-26
  11. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  12. ^ a b "Naming Stars". Retrieved 26 February 2018.
  13. ^ 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.
  14. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  15. ^ 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
  16. ^ 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.
  17. ^ Gamma 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)
  18. ^ (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.
  19. ^ (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.
  20. ^ 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. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146. Vizier catalog entry
  21. ^ 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.
  22. ^ "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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