Sigma Andromedae

Sigma Andromedae is a single^[10] star in the northern constellation of Andromeda. Its Bayer designation is Latinized from σ Andromedae, and abbreviated Sig And or σ And, respectively. The star has an apparent visual magnitude of +4.5,^[2] which is bright enough to be seen with the naked eye from most locations. Parallax measurements made during the Gaia mission place it at a distance of about 140 light-years (43 parsecs).^[1] The magnitude of the star is diminished by 0.08 from extinction caused by intervening gas and dust.^[11] It is drifting closer to the Sun with a radial velocity of –8 km/s.^[2]

Sigma Andromedae

Location of σ Andromedae (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Andromeda
Right ascension	00h 18m 19.65737s[1]
Declination	+36° 47′ 06.8085″[1]
Apparent magnitude (V)	+4.51[2]
Characteristics
Evolutionary stage	main sequence[3]
Spectral type	A2 V[4]
U−B color index	+0.07[5]
B−V color index	+0.05[5]
Astrometry
Radial velocity (Rv)	–8.0[2] km/s
Proper motion (μ)	RA: −65.212(153)[1] mas/yr Dec.: −42.221(124)[1] mas/yr
Parallax (π)	23.2542±0.1809 mas[1]
Distance	140 ± 1 ly (43.0 ± 0.3 pc)
Absolute magnitude (MV)	1.33[6]
Details
Mass	2.12±0.01[3] M☉
Radius	2.13[7] R☉
Luminosity	21.23[7] L☉
Surface gravity (log g)	4.02[6] cgs
Temperature	8,929[6] K
Rotational velocity (v sin i)	123[8] km/s
Age	450[7] Myr
Other designations
σ And, 25 Andromedae, BD+35°44, FK5 1005, HD 1404, HIP 1473, HR 68, SAO 53798, PPM 65183[9]
Database references
SIMBAD	data

This star has a stellar classification of A2 V,^[4] which matches the spectrum of an A-type main sequence star. It is about 450 million years old^[12] and is spinning rapidly with a projected rotational velocity of 123 km/s.^[8] The star has 2.12^[3] times the mass of the Sun and 2.13^[7] times the Sun's girth. It is radiating 21^[7] times the luminosity of the Sun from its photosphere at an effective temperature of 8,929 K,^[6] giving it the white-hued glow of an A-type star.^[13]

In the past, radial velocity variations have been reported,^[14] but this remains unconfirmed.^[10] The star does not show any significant photometric variations and is used as an ubvy standard star.^[15] A debris disk of warm dust around this star has been detected by Spitzer Space Telescope.^[16][17] A model fit to the data yields an orbital distance of 20.3 AU from the host star with a mean temperature of 132.9 K.^[7]

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.^[6]

Naming

In Chinese, 天廄 (Tiān Jiù), meaning Celestial Stable, refers to an asterism consisting of σ Andromedae, θ Andromedae, ρ Andromedae and seven other fainter, unidentified stars. Consequently, the Chinese name for σ Andromedae itself is 天廄三 (Tiān Jiù sān, English: the Third Star of Celestial Stable.)^[18]