Epoch J2000.0 Equinox J2000.0
|Right ascension||00h 18m 19.65745s|
|Declination||+36° 47′ 06.8107″|
|Apparent magnitude (V)||+4.51|
|Spectral type||A2 V|
|U−B color index||+0.07|
|B−V color index||+0.05|
|Radial velocity (Rv)||–8.0 km/s|
|Proper motion (μ)||RA: –65.67 mas/yr
Dec.: -42.00 mas/yr
|Parallax (π)||24.20 ± 0.21 mas|
|Distance||135 ± 1 ly
(41.3 ± 0.4 pc)
|Absolute magnitude (MV)||1.33|
|Surface gravity (log g)||4.02 cgs|
|Rotational velocity (v sin i)||123 km/s|
Sigma Andromedae (σ And, σ Andromedae) is the Bayer designation for a star in the northern constellation of Andromeda. It has an apparent visual magnitude of +4.5, which is bright enough to be seen with the naked eye from most locations. Parallax measurements made during the Hipparcos mission place it at a distance of about 135 light-years (41 parsecs). The magnitude of the star is diminished by 0.08 from extinction caused by intervening gas and dust.
This star has a stellar classification of A2 V, which matches the spectrum of an A-type main sequence star. It is about 450 million years old and is spinning rapidly with a projected rotational velocity of 123 km/s. The interferometry-measured angular diameter of this star is 0.465 mas, which, at its estimated distance, equates to a physical radius of about 2.1 times the radius of the Sun. It is radiating 26 times the luminosity of the Sun from its outer atmosphere at a temperature of 8,929 K, giving it the white-hued glow of an A-type star.
In the past, radial velocity variations have been reported, but this remains unconfirmed. The star does not show any significant photometric variations and is used as a ubvy standard star. Sigma Andromedae is a candidate for membership in the stream of stars associated with the Ursa Major Moving Group. This is a set of stars that share a common motion through space, which suggests they originated together.
In Chinese, 天廄 (Tiān Jiù), meaning Celestial Stable, refers to an asterism consisting of σ Andromedae, θ Andromedae and ρ Andromedae. Consequently, σ Andromedae itself is known as 天廄三 (Tiān Jiù sān, English: the Third Star of Celestial Stable.)
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- (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 18 日