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.)
- van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv: , Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
- Wielen, R.; et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W.
- Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819.
- Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J.
- King, Jeremy R.; et al. (April 2003), "Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group", The Astronomical Journal, 125 (4): 1980–2017, Bibcode:2003AJ....125.1980K, doi:10.1086/368241.
- Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
- van Belle, G. T.; et al. (May 2008), "The Palomar Testbed Interferometer Calibrator Catalog", The Astrophysical Journal Supplement Series, 176 (1): 276–292, arXiv: , Bibcode:2008ApJS..176..276V, doi:10.1086/526548.
- Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv: , Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224.
- Vican, Laura (June 2012), "Age Determination for 346 Nearby Stars in the Herschel DEBRIS Survey", The Astronomical Journal, 143 (6): 135, arXiv: , Bibcode:2012AJ....143..135V, doi:10.1088/0004-6256/143/6/135.
- "sig And -- Variable Star", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-06-24.
- "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-06-24.
- Lehmann, H.; et al. (August 1995), "Variability investigations of possible Maia stars", Astronomy and Astrophysics, 300: 783, Bibcode:1995A&A...300..783L
- (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 18 日