Alpha Aquarii

Quality 0.50 · 1 view · Updated 2 months ago

Star in the constellation Aquarius

title: "Alpha Aquarii" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["g-type-supergiants", "double-stars", "aquarius-(constellation)", "bayer-objects", "bright-star-catalogue-objects", "durchmusterung-objects", "flamsteed-objects", "henry-draper-catalogue-objects", "hipparcos-objects", "stars-with-proper-names", "population-i-stars"] description: "Star in the constellation Aquarius" topic_path: "science/astronomy" source: "https://en.wikipedia.org/wiki/Alpha_Aquarii" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Star in the constellation Aquarius ::

| image= |image=Aquarius constellation map.svg|alt=|float=center|width=280 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=α Aqr |x=555|y=302 |caption=Location of α Aquarii (circled) | epoch = J2000 | constell = Aquarius | ra = | dec = | appmag_v = 2.942 | class = G2 Ib | u-b = +0.699 | b-v = +0.971 | r-i = +0.49 |type=Yellow supergiant}} | radial_v = 7.5 | prop_mo_ra = +18.59 | prop_mo_dec = | pm_footnote = | parallax = 4.9451 | p_error = 0.4296 | parallax_footnote = | dist_pc = | dist_ly = | dist_footnote = | absmag_v = | mass = 6.31 | radius = | luminosity = 3,917 | gravity = 1.4 | temperature = | metal_fe = +0.17 | rotational_velocity = | age_myr = 53 | names = | Simbad = alpha+aquarii

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 . At an apparent visual magnitude of 2.94, 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 ly. It is drifting further away from the Sun with a radial velocity of 7.5 km/s.

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 "the lucky [star] of the king". The name Rucbah had also been applied to this star; though it shared that 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 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) 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).

In Chinese, 危宿 (Wēi Xiù), meaning Rooftop (asterism), refers to an asterism consisting of Alpha Aquarii, Theta Pegasi and Epsilon Pegasi. Consequently, the Chinese name for Alpha Aquarii itself is 危宿一 (Wēi Xiù yī, ).

Properties

With an age of 53 million years, Alpha Aquarii has evolved into a supergiant with a stellar classification of G2 Ib. 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. The star has a massive stellar wind that reaches supersonic velocity in the chromosphere.

There is some uncertainty about Alpha Aquarii's distance. The original Hipparcos catalog gave a parallax of , which translates to a distance of , or 760 light-years. However, the 2007 Hipparcos reduction give a parallax that implies a distance of , or 520 light-years. The third Gaia data release (Gaia DR3) give a parallax of , translating to a distance of , or 660 light-years.

Alpha Aquarii's angular diameter has been measured at . This diameter, at its estimated distance, translates to a radius of times the radius of the Sun. With insufficient mass to explode as a supernova, it will most likely become a massive white dwarf similar to Sirius B. It is radiating 3,900 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of . 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.

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°. However, the pair is only a visual double, with UCAC2 31789179 being a background star.

References

References

  1. pp. 51, 148, [https://books.google.com/books?id=5xQuAAAAIAAJ ''Star-names and Their Meanings''], Richard Hinckley Allen, New York: G. E. Stechert, 1899.
  2. {{in lang. zh ''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.
  3. {{in lang. zh [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_s.htm 香港太空館 - 研究資源 - 亮星中英對照表] {{webarchive. link. (2010-08-18 , Hong Kong Space Museum. Accessed on line November 23, 2010.)
  4. (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.
  5. {{Cite DR3. 2680356911816018048
  6. van Leeuwen, F.. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics.
  7. (February 2010). "Accurate fundamental parameters for A-, F- and G-type Supergiants in the solar neighbourhood". [[Monthly Notices of the Royal Astronomical Society]].
  8. (1999). "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions". Astronomisches Rechen-Institut Heidelberg.
  9. (1984). "Standardization of Broadband Photometry of Equatorial Standards". South African Astronomical Observatory Circulars.
  10. "Alpha Aquarii".
  11. "UCAC2 31789179".
  12. Ayres, Thomas. (2023-05-01). "In the Trenches of the Solar-Stellar Connection. VII. Wilson-Bappu 2022". The Astrophysical Journal Supplement Series.
  13. (December 21, 2004). "The Colour of Stars". [[Commonwealth Scientific and Industrial Research Organisation]].
  14. (2008). "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants". Astronomy and Astrophysics.
  15. (July 2005). "Chandra Observations of Coronal Emission from the Early G Supergiants α and β Aquarii". The Astrophysical Journal.
  16. 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.
  17. (2023-12-01). "33 New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble". The Astronomical Journal.

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::

g-type-supergiantsdouble-starsaquarius-(constellation)bayer-objectsbright-star-catalogue-objectsdurchmusterung-objectsflamsteed-objectshenry-draper-catalogue-objectshipparcos-objectsstars-with-proper-namespopulation-i-stars