Sigma Andromedae
Star in the constellation Andromeda
From Wikipedia, the free encyclopedia
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]
 | |
| 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]