# Sigma Andromedae

Observation data Constellation Epoch J2000.0      Equinox J2000.0 Location of σ Andromedae (circled) Andromeda 00h 18m 19.65745s[1] +36° 47′ 06.8107″[1] +4.51[2] A2 V[3] +0.07[4] +0.05[4] Radial velocity (Rv) –8.0[2] km/s Proper motion (μ) RA: –65.67[1] mas/yr Dec.: -42.00[1] mas/yr Parallax (π) 24.20 ± 0.21[1] mas Distance 135 ± 1 ly (41.3 ± 0.4 pc) Absolute magnitude (MV) 1.33[5] Radius 2.1[6] R☉ Luminosity 26[7] L☉ Surface gravity (log g) 4.02[5] cgs Temperature 8,929[5] K Rotational velocity (v sin i) 123[8] km/s Age 450[9] Myr 25 Andromeda, BD+35°44, FK5 1005, HD 1404, HIP 1473, HR 68, SAO 53798.[10] SIMBAD data

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,[2] 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).[1] The magnitude of the star is diminished by 0.08 from extinction caused by intervening gas and dust.[7]

This star has a stellar classification of A2 V,[3] which matches the spectrum of an A-type main sequence star. It is about 450 million years old[9] and is spinning rapidly with a projected rotational velocity of 123 km/s.[8] The interferometry-measured angular diameter of this star is 0.465 mas,[7] which, at its estimated distance, equates to a physical radius of about 2.1 times the radius of the Sun.[6] It is radiating 26[7] times the luminosity of the Sun from its outer atmosphere at a temperature of 8,929 K,[5] giving it the white-hued glow of an A-type star.[11]

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.[12] 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.[5]

## Naming

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.)[13]

## References

1. 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.
2. ^ a b c 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.
3. ^ a b 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.
4. ^ a b 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.
5. 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.
6. ^ a b 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:
{\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(41.3\cdot 0.465\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 4.13\cdot R_{\bigodot }\end{aligned}}}
7. ^ a b c d 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.
8. ^ a b 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.
9. ^ a b 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.
10. ^ "sig And -- Variable Star", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-06-24.
11. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-06-24.
12. ^ Lehmann, H.; et al. (August 1995), "Variability investigations of possible Maia stars", Astronomy and Astrophysics, 300: 783, Bibcode:1995A&A...300..783L
13. ^