Astronomy:Alpha Aquarii

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Short description: Star in the constellation Aquarius
Alpha Aquarii
Location of α Aquarii (circled)
Observation data
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[1] mas/yr
Dec.: −10.45[1] mas/yr
Parallax (π)4.9451 ± 0.4296[1] mas
Distance691.1+37.8
−56.1 ly
(211.9+11.6
−17.2 pc)
Absolute magnitude (MV)−3.882[5]
Details
Mass6.31[6] M☉
Radius70[7] R☉
Luminosity3,917[6] L☉
Surface gravity (log g)1.4[6] cgs
Temperature5,190±50[8] K
Metallicity [Fe/H]+0.17[5] dex
Rotational velocity (v sin i)6.7±1.5[9] 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, HD 209750, HIP 109074, HR 8414, SAO 145862[10][11][12][13]
Database references
SIMBADdata

Alpha Aquarii is a yellow supergiant star in the constellation of Aquarius. Its identifier is a Bayer designation that is Latinized from α Aquarii, and is abbreviated Alf Aqr or α Aqr, respectively. This star has the official name Sadalmelik, pronounced /ˌsædəlˈmɛlɪk/.[14] At an apparent visual magnitude of 2.94,[2] it is the second-brightest star in Aquarius, just marginally fainter than Beta Aquarii. Based upon parallax measurements made by the Gaia spacecraft, it is located at a distance of roughly 690 light-years (210 parsecs).[15] It is drifting further away from the Sun with a radial velocity of 7.5 km/s.[4]

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" or “arm/support of God”. The name Rucbah had also been applied to this star; though it shared that name with Delta Cassiopeiae.[13] 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.[16] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[17] 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).[14]

In Chinese, 危宿 (Wēi Xiù), meaning Rooftop (asterism), refers to an asterism consisting of Alpha Aquarii, Theta Pegasi and Epsilon Pegasi.[18] Consequently, the Chinese name for Alpha Aquarii itself is 危宿一 (Wēi Xiù yī, English: the First Star of Rooftop).[19]

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.[8] The star has a massive stellar wind that reaches supersonic velocity in the chromosphere.[20]

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.[21] However, the 2007 Hipparcos reduction give a parallax that implies a distance of 161±5 pc, or 520 light-years.[22] 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.[23] This diameter, at its estimated distance,[15] translates to a radius of 70 times the radius of the Sun.[7] With insufficient mass to explode as a supernova, it will most likely become a massive white dwarf similar to Sirius B.[16] It is radiating 3,900 times as much luminosity as the Sun from its outer atmosphere[6] at an effective temperature of 5,190 K.[8] At this heat, the star glows with the yellow hue of a G-type star.[24] 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]

Alpha Aquarii has a visual companion, UCAC2 31789179, of magnitude 12.2. It is at an angular separation of 110.4 arcseconds from Alpha Aquarii along a position angle of 40°.[12] However, the pair is only a visual double, with UCAC2 31789179 being a background star.[25]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars 8: 59, Bibcode: 1984SAAOC...8...59C. 
  3. ↑ 3.0 3.1 3.2 3.3 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, doi:10.1111/j.1365-2966.2009.15979.x, Bibcode: 2010MNRAS.402.1369L. 
  4. ↑ 4.0 4.1 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. ↑ 5.0 5.1 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, doi:10.1051/0004-6361:20078788, Bibcode: 2008A&A...480...91S. 
  6. ↑ 6.0 6.1 6.2 6.3 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, doi:10.3847/1538-4365/acb535, ISSN 0067-0049, Bibcode: 2023ApJS..266....6A.  Alpha Aquarii's database entry at VizieR.
  7. ↑ 7.0 7.1 Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1, https://books.google.com/books?id=OvTjLcQ4MCQC&pg=PA41. . The radius (R*) is given by:
    2⋅R*=(211.9⋅3.066⋅10−3) AU0.0046491 AU/R⨀≈140⋅R⨀
  8. ↑ 8.0 8.1 8.2 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, doi:10.1134/S1063773717110068, Bibcode: 2017AstL...43..751U. 
  9. ↑ 9.0 9.1 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, doi:10.1086/431977, Bibcode: 2005ApJ...627L..53A 
  10. ↑ Hoffleit, D.; Warren, Jr., W. H., "HR 8414, database entry", The Bright Star Catalogue (CDS), http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=V/50/catalog&recno=8414, retrieved 2008-10-03.  ID V/50. Accessed on line October 3, 2008.
  11. ↑ "Alpha Aquarii". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=Alpha+Aquarii. 
  12. ↑ 12.0 12.1 "Entry 22058-0019", The Washington Double Star Catalog (United States Naval Observatory), http://ad.usno.navy.mil/wds/Webtextfiles/wdsnewframe4.html, retrieved 2008-11-18. 
  13. ↑ 13.0 13.1 pp. 51, 148, Star-names and Their Meanings, Richard Hinckley Allen, New York: G. E. Stechert, 1899.
  14. ↑ 14.0 14.1 Naming Stars, IAU.org, https://www.iau.org/public/themes/naming_stars/, retrieved 25 February 2018. 
  15. ↑ 15.0 15.1 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, doi:10.3847/1538-3881/abd806, ISSN 0004-6256, Bibcode: 2021AJ....161..147B.  Data about this star can be seen here.
  16. ↑ 16.0 16.1 Kaler, James. "Sadalsuud". http://stars.astro.illinois.edu/sow/sadalsuud.html. 
  17. ↑ IAU Working Group on Star Names (WGSN), International Astronomical Union, https://www.iau.org/science/scientific_bodies/working_groups/280/, retrieved 22 May 2016. 
  18. ↑ (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.
  19. ↑ (in 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.
  20. ↑ 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, 18.07, Bibcode: 1993AAS...183.1807D. 
  21. ↑ 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, ISSN 1609-042X, Bibcode: 1997ESASP1200.....E, https://ui.adsabs.harvard.edu/abs/1997ESASP1200.....E. 
  22. ↑ van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V. 
  23. ↑ 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, doi:10.3847/1538-3881/ad08be, ISSN 0004-6256, Bibcode: 2023AJ....166..268B. 
  24. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16. 
  25. ↑ "UCAC2 31789179". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=UCAC2+31789179. 

Coordinates: Sky map 22h 05m 47.03593s, −00° 19′ 11.4568″



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