Epoch J2000.0 Equinox J2000.0 (ICRS)
|Right ascension||22h 05m 47.03593s|
|Declination||−00° 19′ 11.4568″|
|Apparent magnitude (V)||2.942|
|Spectral type||G2 Ib|
|U−B color index||+0.699|
|B−V color index||+0.971|
|R−I color index||+0.49|
|Radial velocity (Rv)||7.5 km/s|
|Proper motion (μ)||RA: +18.25 mas/yr
Dec.: −9.39 mas/yr
|Parallax (π)||6.23 ± 0.19 mas|
|Distance||520 ± 20 ly
(161 ± 5 pc)
|Absolute magnitude (MV)||–3.882|
|Mass||6.5 ± 0.3 M☉|
|Radius||77 ± 15 R☉|
|Surface gravity (log g)||1.76 ± 0.04 cgs|
|Temperature||5,210 ± 100 K|
|Rotational velocity (v sin i)||6.7 ± 1.5 km/s|
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 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.
With an age of 53 million years, this star has evolved into a supergiant with a stellar classification of G2 Ib. It has 6.5 as much mass as the Sun and has expanded to around 77 times the Sun's radius. It is radiating 3,000 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 5,210 K. At this heat, the star glows with the yellow hue of a G-type star. 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.
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°.
The name Sadalmelik derives from an Arabic expression سعد الملك sa‘d al-malik meaning "Luck of the king". Ulug Beg was combined the name with ο Aqr. The name Rucbah has also been applied to this star; it shares this name with Delta Cassiopeiae. 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.
In Chinese, 危宿 (Wēi Xiù), meaning Rooftop (asterism), refers to an asterism consisting of α Aquarii, θ Pegasi and ε Pegasi. Consequently, α Aquarii itself is known as 危宿一 (Wēi Xiù yī, English: the First Star of Rooftop.)
- 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
- A. W. J. (1984), Standardization of Broadband Photometry of Equatorial Standards, South African Astronomical Observatory Circulars 8: 59, Bibcode:1984SAAOC...8...59C Unknown parameter
- 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
- 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.
- 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
- 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.
- 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
- Sadalmelik, Stars, Jim Kaler. Accessed on line October 3, 2008.
- 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
- NAME SADALMELIK -- Star in double system, database entry, SIMBAD. Accessed on line October 3, 2008.
- Entry 22058-0019, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line November 18, 2008.
- pp. 51, 148, Star-names and Their Meanings, Richard Hinckley Allen, New York: G. E. Stechert, 1899.
- The Colour of Stars, Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16
- (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.
- (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.