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]

Gamma Aquarii (γ Aqr, γ Aquarii) is the Bayer designation for a star in the constellation Aquarius. It has the traditional name Sadachbia, from an Arabic expression سعد الأخبية sa‘d al-’axbiyah "luck of the homes (tents)". In Hindi it is also called Satabhishaj (a hundred physicians); Sadhayam in Tamil. This star 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.

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).[8] This star, along with π Aqr (Seat), ζ Aqr (Sadaltager / Achr al Achbiya) and η Aqr (Hydria), were al Aḣbiyah (الأخبية), the Tent.[9][10][11]

In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of γ Aquarii, ζ Aquarii, η Aquarii, π Aquarii.[12] Consequently, γ Aquarii itself is known as 墳墓二 (Fén Mù èr, English: the Second Star of Tomb).[13]

Gamma Aquarii is an A-type main sequence star with a stellar classification of A0 V,[3] making it both larger and more massive than the Sun. It is a candidate Lambda Boötis star, suggesting it may have accreted low-metallicity circumstellar gas some time in the past.[14] 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.[15]


  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:1953QB901.W495...... 
  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, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224. 
  7. ^ "gam Aqr -- Star in double system", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg). 
  8. ^ 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. 
  9. ^ 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 
  10. ^ 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. 
  11. ^ γ Aqr as Aoul al Achbiya or Prima Tabernaculorum (the first of luck of the homes or tents), π Aqr as Wasat al Achbiya or Media Tabernaculorum (the middle of luck of the homes or tents) and ζ Aqr as Achr al Achbiya or Postrema Tabernaculorum (the end of luck of the homes or tents). η Aqr should be designated as al Achbiya consistently, but it was not designated as the Arabic name except the name Hydria (Greek) or Deli (Hebrew)
  12. ^ (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.
  13. ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
  14. ^ 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. 
  15. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16. 

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