Observation data Epoch J2000.0 Equinox J2000.0 ( ICRS) | |
---|---|
Constellation | Aquarius |
Right ascension | 22h 05m 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 | |
Database references | |
SIMBAD | data |
Alpha Aquarii, officially named Sadalmelik ( /ˌsædəlˈmɛlɪk/), [12] is a single 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 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 ( 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". 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]
In Chinese, 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 temperature of 5,383 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]
Observation data Epoch J2000.0 Equinox J2000.0 ( ICRS) | |
---|---|
Constellation | Aquarius |
Right ascension | 22h 05m 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 | |
Database references | |
SIMBAD | data |
Alpha Aquarii, officially named Sadalmelik ( /ˌsædəlˈmɛlɪk/), [12] is a single 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 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 ( 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". 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]
In Chinese, 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 temperature of 5,383 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]