Alpha Aquarii
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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 Template:IPAc-en.[1] 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 Template:Convert.[3] 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 "the lucky [star] of the king". The name Rucbah had also been applied to this star; though it shared that name with Delta Cassiopeiae.[5] 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.[6] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[7] 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).[1]
In Chinese, Template:Lang (Template:Lang), meaning Rooftop (asterism), refers to an asterism consisting of Alpha Aquarii, Theta Pegasi and Epsilon Pegasi.[8] Consequently, the Chinese name for Alpha Aquarii itself is Template:Lang (Template:Lang, Template:Langx).[9]
Properties
With an age of 53 million years,[10] Alpha Aquarii has evolved into a supergiant with a stellar classification of G2 Ib.[10] 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.[11] The star has a massive stellar wind that reaches supersonic velocity in the chromosphere.[12]
There is some uncertainty about Alpha Aquarii's distance. The original Hipparcos catalog gave a parallax of Template:Val, which translates to a distance of Template:Val, or 760 light-years.[13] However, the 2007 Hipparcos reduction give a parallax that implies a distance of Template:Val, or 520 light-years.[14] The third Gaia data release (Gaia DR3) give a parallax of Template:Val, translating to a distance of Template:Val, or 660 light-years.[15]
Alpha Aquarii's angular diameter has been measured at Template:Val.[16] This diameter, at its estimated distance,[3] translates to a radius of Template:Solar radius calculator times the radius of the Sun.[17] With insufficient mass to explode as a supernova, it will most likely become a massive white dwarf similar to Sirius B.[6] It is radiating 3,900 times as much luminosity as the Sun from its outer atmosphere[18] at an effective temperature of Template:Val.[11] At this heat, the star glows with the yellow hue of a G-type star.[19] 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.[20]
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°.[21] However, the pair is only a visual double, with UCAC2 31789179 being a background star.[22]
References
External links
- Alpha Aquarii Aladin image viewer
Template:Sky Template:Stars of Aquarius
- ↑ 1.0 1.1 Cite error: Invalid
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<ref>tag; no text was provided for refs named "scfs". - ↑ pp. 51, 148, Star-names and Their Meanings, Richard Hinckley Allen, New York: G. E. Stechert, 1899.
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- ↑ Template:In lang 香港太空館 - 研究資源 - 亮星中英對照表 Template:Webarchive, Hong Kong Space Museum. Accessed on line November 23, 2010.
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