Alpha Aquarii
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]
Characteristics
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[2]
Astrometry
Radial velocity (Rv)7.5[4] km/s
Proper motion (μ) RA: +18.25[1] mas/yr
Dec.: −9.39[1] mas/yr
Parallax (π)6.23 ± 0.19 mas[1]
Distance520 ± 20 ly
(161 ± 5 pc)
Absolute magnitude (MV)−3.882[5]
Details
Mass5.13±0.06[6] M☉
Radius52.89+1.68
−1.78[6] R☉
Luminosity2,120±167[6] L☉
Surface gravity (log g)1.76±0.04[3] cgs
Temperature5,383±74[6] K
Metallicity [Fe/H]+0.17[5] dex
Rotational velocity (v sin i)6.7±1.5[7] km/s
Age53[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, Gaia DR2 2680356911815074432, HD 209750, HIP 109074, HR 8414, SAO 145862, WDS 22058-0019, 2MASS J22054703-0019114[8][9][10][11]
Database references
SIMBADdata

Alpha Aquarii, officially named Sadalmelik (/ˌsædəlˈmɛlɪk/),[12] is a single star in the constellation of Aquarius. 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, it is located at a distance of roughly 520 light-years (160 parsecs) from the Sun.[1] It is drifting further away from the Sun with a radial velocity of 7.5 km/s.[4]

It forms the primary or 'A' component of a double star designated WDS J22058-0019; the secondary or 'B' component is UCAC2 31789179.[13]

Nomenclature

α Aquarii (Latinised to Alpha Aquarii) is the star's Bayer designation. WDS J22058-0019 A is its designation in the Washington Double Star Catalog.

It bore the traditional name Sadalmelik, which derived from an Arabic expression سعد الملك (sa‘d al-malik), meaning "Luck of the king". The name Rucbah had also been applied to this star; though it shared that name with Delta Cassiopeiae.[11] 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.[14] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[15] to catalogue and standardize proper names for stars. The WGSN approved the name Sadalmelik for Alpha Aquarii (WDS J22058-0019 A) on 21 August 2016, and it is now so included in the List of IAU-approved Star Names (Delta Cassiopeiae was given the name Ruchbah).[12]

In Chinese, 危宿 (Wēi Xiù), meaning Rooftop (asterism), refers to an asterism consisting of Alpha Aquarii, Theta Pegasi and Epsilon Pegasi.[16] Consequently, the Chinese name for Alpha Aquarii itself is 危宿一 (Wēi Xiù yī, English: the First Star of Rooftop).[17]

Properties

With an age of 53 million years,[3] Alpha Aquarii has evolved into a supergiant with a stellar classification of G2 Ib.[3] It lies within the Cepheid instability strip of the Hertzsprung–Russell diagram, near the red (cooler) edge, but is not classified as a variable star. However, variable cores have been detected in the hydrogen lines, which are originating in a circumstellar envelope.[18] The star has a massive stellar wind that reaches supersonic velocity in the chromosphere.[19]

Alpha Aquarii has 5.1[6] times as much mass as the Sun and has expanded to around 53[6] times the Sun's radius. It is radiating 2,100[6] times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 5,383 K.[6] At this heat, the star glows with the yellow hue of a G-type star.[20] 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.[7]

The visual companion (UCAC2 31789179) has an apparent visual magnitude of approximately 12.2. It is at an angular separation of 110.4 arcseconds from Alpha Aquarii along a position angle of 40°.[10]

References

  1. 1 2 3 4 5 6 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, S2CID 18759600
  2. 1 2 3 4 5 Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars, 8: 59, Bibcode:1984SAAOC...8...59C
  3. 1 2 3 4 5 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, S2CID 119096173
  4. 1 2 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
  5. 1 2 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. S2CID 16602121.
  6. 1 2 3 4 5 6 7 8 Baines, Ellyn K.; et al. (2018). "Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer". The Astronomical Journal. 155 (1). 30. arXiv:1712.08109. Bibcode:2018AJ....155...30B. doi:10.3847/1538-3881/aa9d8b.
  7. 1 2 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, S2CID 122519436
  8. ↑ 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.
  9. ↑ NAME SADALMELIK -- Star in double system, database entry, SIMBAD. Accessed on line October 3, 2008.
  10. 1 2 Entry 22058-0019, The Washington Double Star Catalog Archived 2009-01-31 at the Wayback Machine, United States Naval Observatory. Accessed on line November 18, 2008.
  11. 1 2 pp. 51, 148, Star-names and Their Meanings, Richard Hinckley Allen, New York: G. E. Stechert, 1899.
  12. 1 2 "Naming Stars". IAU.org. Retrieved 25 February 2018.
  13. ↑ "UCAC2 31789179 -- Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2018-02-25
  14. ↑ Sadalmelik, Stars, Jim Kaler. Accessed on line October 3, 2008.
  15. ↑ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  16. ↑ (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.
  17. ↑ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2010-08-18 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  18. ↑ Usenko, I. A.; et al. (November 2017), "Spectroscopic studies of the unique yellow supergiant α Aqr in the Cepheid instability strip", Astronomy Letters, 43 (11): 751–767, Bibcode:2017AstL...43..751U, doi:10.1134/S1063773717110068, S2CID 41734976.
  19. ↑ Dupree, A. K.; et al. (December 1993), "HST/GHRS Spectroscopy of the Hybrid Star Alpha Aquarii", Bulletin of the American Astronomical Society, American Astronomical Society, 183rd AAS Meeting, 25: 1321, Bibcode:1993AAS...183.1807D, 18.07.
  20. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on February 22, 2012, retrieved 2012-01-16
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