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Alpha Aquarii

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Alpha Aquarii, officially named Sadalmelik (/ˌsædəlˈmɛlɪk/),[15] is a single yellow supergiant 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 by the Gaia spacecraft, it is located at a distance of roughly 690 light-years (210 parsecs) from the Sun.[5] It is drifting further away from the Sun with a radial velocity of 7.5 km/s.[4]

Alpha Aquarii
Location of α Aquarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Aquarius
Right ascension 22h 05m 47.03555s[1]
Declination −00° 19′ 11.4634″[1]
Apparent magnitude (V) 2.942[2]
Characteristics
Evolutionary stage Yellow supergiant
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: +18.59 mas/yr[1]
Dec.: −10.45 mas/yr[1]
Parallax (π)4.9451 ± 0.4296 mas[1]
Distance690.8+37.8
−56.1 ly
(211.9+11.6
−17.2 pc)[5]
Absolute magnitude (MV)−3.882[6]
Details
Mass6.31[7] M☉
Radius70[8] R☉
Luminosity3,917[7] L☉
Surface gravity (log g)1.4[7] cgs
Temperature5,190±50[9] K
Metallicity [Fe/H]+0.17[6] dex
Rotational velocity (v sin i)6.7±1.5[10] 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[11][12][13][14]
Database references
SIMBADdata

It forms the primary or 'A' component of a double star designated WDS J22058-0019; the secondary or 'B' component is UCAC2 31789179.[16] However, the pair is only an optical binary, with UCAC2 31789179 being a background star.[16]

Nomenclature

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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" or “arm/support of God”. The name Rucbah had also been applied to this star; though it shared that name with Delta Cassiopeiae.[14] 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.[17] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[18] 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).[15]

In Chinese, 危宿 (Wēi Xiù), meaning Rooftop (asterism), refers to an asterism consisting of Alpha Aquarii, Theta Pegasi and Epsilon Pegasi.[19] Consequently, the Chinese name for Alpha Aquarii itself is 危宿一 (Wēi Xiù yī, English: the First Star of Rooftop).[20]

Properties

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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.[9] The star has a massive stellar wind that reaches supersonic velocity in the chromosphere.[21]

There is some uncertainty about Alpha Aquarii's distance. The original Hipparcos catalog gave a parallax of 4.3±0.83 mas, which translates to a distance of 233±45 parsecs, or 760 light-years.[22] However, the 2007 Hipparcos reduction give a parallax that implies a distance of 161±5 pc, or 520 light-years.[23] The third Gaia data release (Gaia DR3) give a parallax of 4.94±0.43 mas, translating to a distance of 202±17 pc, or 660 light-years.[1]

Alpha Aquarii's angular diameter has been measured at 3.066±0.036 mas.[24] At its estimated distance,[5] it translates to a radius of 70 times the radius of the Sun.[8] With insufficient mass to explode as a supernova, it will most likely become a massive white dwarf similar to Sirius B.[25] It is radiating 3,900 times as much luminosity as the Sun from its outer atmosphere[7] at an effective temperature of 5,190 K.[9] At this heat, the star glows with the yellow hue of a G-type star.[26] 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.[10]

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°.[13]

References

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  1. ^ a b c d e Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ a b c d e 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 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. ^ a b Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, 35 (35), Astronomisches Rechen-Institut Heidelberg: 1, Bibcode:1999VeARI..35....1W
  5. ^ a b c Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Demleitner, M.; Andrae, R. (2021-03-01). "Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3". The Astronomical Journal. 161 (3): 147. arXiv:2012.05220. Bibcode:2021AJ....161..147B. doi:10.3847/1538-3881/abd806. ISSN 0004-6256. Data about this star can be seen here.
  6. ^ a b 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.
  7. ^ a b c d Ayres, Thomas (2023-05-01). "In the Trenches of the Solar-Stellar Connection. VII. Wilson-Bappu 2022". The Astrophysical Journal Supplement Series. 266 (1): 6. Bibcode:2023ApJS..266....6A. doi:10.3847/1538-4365/acb535. ISSN 0067-0049. Alpha Aquarii's database entry at VizieR.
  8. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
     
  9. ^ a b c 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.
  10. ^ 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, S2CID 122519436
  11. ^ 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.
  12. ^ "Alpha Aquarii". SIMBAD. Centre de données astronomiques de Strasbourg.
  13. ^ a b 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.
  14. ^ a b pp. 51, 148, Star-names and Their Meanings, Richard Hinckley Allen, New York: G. E. Stechert, 1899.
  15. ^ a b "Naming Stars". IAU.org. Retrieved 25 February 2018.
  16. ^ a b "UCAC2 31789179 -- Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2018-02-25
  17. ^ Sadalmelik, Stars, Jim Kaler. Accessed on line October 3, 2008.
  18. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  19. ^ (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.
  20. ^ (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.
  21. ^ Dupree, A. K.; et al. (December 1993), "HST/GHRS Spectroscopy of the Hybrid Star Alpha Aquarii", Bulletin of the American Astronomical Society, 25, American Astronomical Society, 183rd AAS Meeting: 1321, Bibcode:1993AAS...183.1807D, 18.07.
  22. ^ ESA (1997-01-01). "The HIPPARCOS and TYCHO catalogues. Astrometric and photometric star catalogues derived from the ESA HIPPARCOS Space Astrometry Mission". ESA Special Publication. 1200. Bibcode:1997ESASP1200.....E. ISSN 1609-042X.
  23. ^ 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
  24. ^ Baines, Ellyn K.; Clark III, James H.; Schmitt, Henrique R.; Stone, Jordan M.; von Braun, Kaspar (2023-12-01). "33 New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble". The Astronomical Journal. 166 (6): 268. Bibcode:2023AJ....166..268B. doi:10.3847/1538-3881/ad08be. ISSN 0004-6256.
  25. ^ "Sadalsuud". stars.astro.illinois.edu. Retrieved 2024-08-04.
  26. ^ "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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