Alpha Aquarii

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

Location of α Aquarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Aquarius
Right ascension 22h 05m 47.03593s[1]
Declination −00° 19′ 11.4568″[1]
Apparent magnitude (V) 2.942[2]
Spectral type G2 Ib[3]
U−B color index +0.699[2]
B−V color index +0.971[2]
R−I color index +0.49[4]
Radial velocity (Rv) 7.5[5] km/s
Proper motion (μ) RA: +18.25[1] mas/yr
Dec.: −9.39[1] mas/yr
Parallax (π) 6.23 ± 0.19[1] mas
Distance 520 ± 20 ly
(161 ± 5 pc)
Absolute magnitude (MV) –3.882[6]
Mass 6.5 ± 0.3[3] M
Radius 77 ± 15[7] R
Luminosity 3000[8] L
Surface gravity (log g) 1.76 ± 0.04[3] cgs
Temperature 5,210 ± 100[3] K
Rotational velocity (v sin i) 6.7 ± 1.5[9] km/s
Age 53[3] Myr
Other designations
El Melik, Rucbah, Saad el Melik, Sadalmelek, Sadalmelik, Sadlamulk, α Aqr, Alpha Aquarii, Alpha Aqr, 34 Aquarii, 34 Aqr, BD−01 4246, FK5 827, HD 209750, HIP 109074, HR 8414, SAO 145862.[4][10][11][12]
Database references

Alpha Aquarii (Alpha Aqr, α Aquarii, α Aqr) is a single star in the Aquarius. It has the traditional name Sadalmelik, which is derived from Arabic for "Luck of the king". The apparent visual magnitude of 2.94[2] makes this the second-brightest star in Aquarius. Based upon parallax measurements made during the Hipparcos mission, this star is located at a distance of roughly 520 light-years (160 parsecs) from Earth.[1]

With an age of 53 million years,[3] this star has evolved into a supergiant with a stellar classification of G2 Ib.[3] It has 6.5[3] times as much mass as the Sun and has expanded to around 77[7] times the Sun's radius. It is radiating 3,000[8] times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 5,210 K.[3] At this heat, the star glows with the yellow hue of a G-type star.[13] Examination of this star with the Chandra X-ray Observatory shows it to be significantly X-ray deficient compared to G-type main sequence stars. This deficit is a common feature of early G-type giant stars.[9]

Sadalmelik has a visual companion, designated CCDM J22058-0019B, with an apparent visual magnitude of approximately 12.2. It is at an angular separation of 110.4 arcseconds from Sadalmelik along a position angle of 40°.[11]

The name Sadalmelik derives from an Arabic expression سعد الملك sa‘d al-malik meaning "Luck of the king". The name Rucbah has also been applied to this star; it shares this name with Delta Cassiopeiae.[12] It is only one of two stars with ancient proper names to lie within a degree of the celestial equator. The origin of the Arabic name is lost to history.[8]

In Chinese, 危宿 (Wēi Xiù), meaning Rooftop (asterism), refers to an asterism consisting of α Aquarii, θ Pegasi and ε Pegasi.[14] Consequently, α Aquarii itself is known as 危宿一 (Wēi Xiù yī, English: the First Star of Rooftop.)[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 c d e f g h i Lyubimkov, Leonid S.; et al. (February 2010), "Accurate fundamental parameters for A-, F- and G-type Supergiants in the solar neighbourhood", Monthly Notices of the Royal Astronomical Society 402 (2): 1369–1379, arXiv:0911.1335, Bibcode:2010MNRAS.402.1369L, doi:10.1111/j.1365-2966.2009.15979.x 
  4. ^ a b HR 8414, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line October 3, 2008.
  5. ^ Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb (Astronomisches Rechen-Institut Heidelberg) 35 (35): 1, Bibcode:1999VeARI..35....1W 
  6. ^ Soubiran, C.; et al. (2008). "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants". Astronomy and Astrophysics 480 (1): 91–101. arXiv:0712.1370. Bibcode:2008A&A...480...91S. doi:10.1051/0004-6361:20078788. 
  7. ^ a b Nordgren, Tyler E.; et al. (December 1999), "Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer", The Astronomical Journal 118 (6): 3032–3038, Bibcode:1999AJ....118.3032N, doi:10.1086/301114 
  8. ^ a b c Sadalmelik, Stars, Jim Kaler. Accessed on line October 3, 2008.
  9. ^ a b Ayres, Thomas R.; Brown, Alexander; Harper, Graham M. (July 2005), "Chandra Observations of Coronal Emission from the Early G Supergiants α and β Aquarii", The Astrophysical Journal 627 (1): L53–L56, Bibcode:2005ApJ...627L..53A, doi:10.1086/431977 
  10. ^ NAME SADALMELIK -- Star in double system, database entry, SIMBAD. Accessed on line October 3, 2008.
  11. ^ a b Entry 22058-0019, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line November 18, 2008.
  12. ^ a b pp. 51, 148, Star-names and Their Meanings, Richard Hinckley Allen, New York: G. E. Stechert, 1899.
  13. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16 
  14. ^ (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. ^ (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.

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