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Alpha Aquarii

α Aquarii
Aquarius constellation map.svg
Red circle.svg

Location of α Aquarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Aquarius
Right ascension 22h 05m 47.03593s
Declination −00° 19′ 11.4568″
Apparent magnitude (V) 2.942
Characteristics
Spectral type G2 Ib
U−B color index +0.699
B−V color index +0.971
R−I color index +0.49
Astrometry
Radial velocity (Rv) 7.5 km/s
Proper motion (μ) RA: +18.25 mas/yr
Dec.: −9.39 mas/yr
Parallax (π) 6.23 ± 0.19mas
Distance 520 ± 20 ly
(161 ± 5 pc)
Absolute magnitude (MV) –3.882
Details
Mass 6.5 ± 0.3 M
Radius 77 ± 15 R
Luminosity 3,000 L
Surface gravity (log g) 1.76 ± 0.04 cgs
Temperature 5,210 ± 100 K
Metallicity [Fe/H] +0.17 dex
Rotational velocity (v sin i) 6.7 ± 1.5 km/s
Age 53 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.
Database references
SIMBAD data

Alpha Aquarii (α Aquarii, abbreviated Alpha Aqr, α Aqr), also named Sadalmelik, is a single star in the constellation of Aquarius. The apparent visual magnitude of 2.94 makes this the second-brightest star in Aquarius. Based upon parallax measurements made during the Hipparcos mission, this star is located at a distance of roughly 520 light-years (160 parsecs) from the Sun.

α Aquarii (Latinised to Alpha Aquarii) is the star's Bayer designation.

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. 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 this star on 21 August 2016 and it is now so entered in the IAU Catalog of 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, Alpha Aquarii itself is known as 危宿一 (Wēi Xiù yī, English: the First Star of Rooftop.)


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