Sigma Andromedae

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]

Sigma Andromedae
Location of σ Andromedae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Andromeda
Right ascension  00h 18m 19.65745s[1]
Declination +36° 47′ 06.8107″[1]
Apparent magnitude (V) +4.51[2]
Characteristics
Spectral type A2 V[3]
U−B color index +0.07[4]
B−V color index +0.05[4]
Astrometry
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
Distance135 ± 1 ly
(41.3 ± 0.4 pc)
Absolute magnitude (MV)1.33[5]
Details
Radius2.1[6] R☉
Luminosity26[7] L☉
Surface gravity (log g)4.02[5] cgs
Temperature8,929[5] K
Rotational velocity (v sin i)123[8] km/s
Age450[9] Myr
Other designations
25 Andromeda, BD+35°44, FK5 1005, HD 1404, HIP 1473, HR 68, SAO 53798.[10]
Database references
SIMBADdata

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 an ubvy standard star.[12] A debris disk of warm dust around this star has been detected by Spitzer Space Telescope.[13]

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, the Chinese name for σ Andromedae itself is 天廄三 (Tiān Jiù sān, English: the Third Star of Celestial Stable.)[14]

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References
  1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg, Astronomisches Rechen-Institut Heidelberg, 35 (35): 1, Bibcode:1999VeARI..35....1W.
  3. 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. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 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. 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:
  7. van Belle, G. T.; et al. (May 2008), "The Palomar Testbed Interferometer Calibrator Catalog", The Astrophysical Journal Supplement Series, 176 (1): 276–292, arXiv:0711.4194, Bibcode:2008ApJS..176..276V, doi:10.1086/526548.
  8. 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:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224.
  9. Vican, Laura (June 2012), "Age Determination for 346 Nearby Stars in the Herschel DEBRIS Survey", The Astronomical Journal, 143 (6): 135, arXiv:1203.1966, Bibcode:2012AJ....143..135V, doi:10.1088/0004-6256/143/6/135.
  10. "sig And". SIMBAD. 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. Morales, F.Y.; et al. (July 2009), "Spitzer Mid-IR Spectra of Dust Debris Around A and Late B Type Stars: Asteroid Belt Analogs and Power-Law Dust Distributions" (PDF), The Astrophysical Journal, 699 (2): 1067–1086, Bibcode:2009ApJ...699.1067M, doi:10.1088/0004-637X/699/2/1067
  14. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 18 日
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