22h05m47.03593s, −00° 19′ 11.4568″
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| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 22h05m 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] |
| Distance | 520 ± 20 ly (161 ± 5 pc) |
| Absolute magnitude (MV) | −3.882[5] |
| Details | |
| Mass | 5.13±0.06[6] M☉ |
| Radius | 52.89+1.68 −1.78[6] R☉ |
| Luminosity | 2,120±167[6] L☉ |
| Surface gravity (log g) | 1.76±0.04[3] cgs |
| Temperature | 5,383±74[6] K |
| Metallicity [Fe/H] | +0.17[5] dex |
| Rotational velocity (v sin i) | 6.7±1.5[7] km/s |
| Age | 53[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 | |
| SIMBAD | data |
Alpha Aquarii, officially named Sadalmelik (/ˌsædəlˈmɛlɪk/),[12] is a single star in the constellationofAquarius. 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]
α Aquarii (LatinisedtoAlpha 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]
InChinese, 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]
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 temperatureof5,383 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]
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