Beta Pegasi

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Beta Pegasi
Pegasus constellation map.svg
Red circle.svg

Location of β Pegasi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Pegasus
Right ascension 23h 03m 46.45746s[1]
Declination +28° 04′ 58.0336″[1]
Apparent magnitude (V) 2.42[2] (2.31 - 2.74[3]
Spectral type M2.5II–IIIe[4]
U−B color index +1.96[2]
B−V color index +1.67[2]
Variable type Semi-regular[5]
Radial velocity (Rv) +8.7[6] km/s
Proper motion (μ) RA: +187.65[1] mas/yr
Dec.: +136.93[1] mas/yr
Parallax (π) 16.64 ± 0.15[1] mas
Distance 196 ± 2 ly
(60.1 ± 0.5 pc)
Absolute magnitude (MV) -1.49
Mass 2.1[7] M
Radius 95[8] R
Surface gravity (log g) 1.20[9] cgs
Temperature 3,689[9] K
Metallicity [Fe/H] –0.11[9] dex
Rotational velocity (v sin i) 9.7[10] km/s
Other designations
Scheat, 53 Peg, HR 8775, BD +27°4480, HD 217906, SAO 90981, FK5 870, HIP 113881.[4]
Database references

Beta Pegasi (β Peg, β Pegasi) is a red giant star in the constellation Pegasus. The apparent visual magnitude of this star averages 2.42, making it the second brightest star in the constellation after Epsilon Pegasi. Its traditional name is Scheat,[11] a name that has also been used for Delta Aquarii. According to Richard H. Allen, this name comes from the Arabic Al Sā'id for "the upper arm", or from Sa'd. Arabian astronomers named it Mankib al Faras, meaning the "Horse's shoulder". It forms the upper right corner of the Great Square of Pegasus,[11] a prominent rectangular asterism.

Based upon parallax measurements, Beta Pegasi is located about 196 light-years (60 parsecs) from the Earth.[1] It is unusual among bright stars in having a relatively cool surface temperature compared to stars like the Sun.[8] This star has a stellar classification of M2.3 II–III,[4] which indicates the spectrum has characteristics partway between a bright giant and a giant star. It has expanded until it is some 95 times as large, and has a total luminosity of 1500 times that of the Sun.[8] The effective temperature of the star's outer envelope is about 3,700 K,[9] giving the star the characteristic orange-red hue of an M-type star.[12] The photosphere is sufficiently cool for molecules of titanium oxide to form.[13]

Beta Pegasi is a semi-regular variable with a period of 43.3 days[5] and a brightness that varies from magnitude +2.31 to +2.74.[3] It is losing mass at a rate at or below 10−8 times the Sun's mass per year, which is creating an expanding shell of gas and dust with a radius of about 3,500 times the Sun's radius (16 Astronomical Units).[14]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752free to read, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c 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. 
  3. ^ a b "Query= bet Peg", General Catalogue of Variable Stars, Centre de Données astronomiques de Strasbourg, retrieved 2010-01-05 
  4. ^ a b c "V* bet Peg -- Pulsating variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2010-01-05 
  5. ^ a b Tabur, V.; et al. (December 2009), "Long-term photometry and periods for 261 nearby pulsating M giants", Monthly Notices of the Royal Astronomical Society, 400 (4): 1945–1961, arXiv:0908.3228free to read, Bibcode:2009MNRAS.400.1945T, doi:10.1111/j.1365-2966.2009.15588.x 
  6. ^ Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Washington, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W 
  7. ^ Tsuji, Takashi (May 2007). "Isotopic abundances of Carbon and Oxygen in Oxygen-rich giant stars". In Kupka, F.; Roxburgh, I.; Chan, K. Convection in Astrophysics, Proceedings of IAU Symposium #239 held 21-25 August, 2006 in Prague, Czech Republic. Proceedings of the International Astronomical Union. 2. pp. 307–310. arXiv:astro-ph/0610180free to read. Bibcode:2007IAUS..239..307T. doi:10.1017/S1743921307000622. 
  8. ^ a b c Kaler, James B. (May 22, 2009), "SCHEAT (Beta Pegasi)", Stars, University of Illinois, retrieved 2010-01-05 
  9. ^ a b c d Soubiran, C.; et al. (2008), "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants", Astronomy and Astrophysics, 480 (1): 91–101, arXiv:0712.1370free to read, Bibcode:2008A&A...480...91S, doi:10.1051/0004-6361:20078788 
  10. ^ Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209 
  11. ^ a b Allen, Richard Hinckley (1899), Star Names: Their Lore and Meaning, New York, NY: Dover Publications Inc., p. 325, ISBN 0-486-21079-0 
  12. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16 
  13. ^ Gavin, M. (February 1996), "Stellar spectroscopy with CCDs - some preliminary results", Journal of the British Astronomical Association, 106 (1): 11–15, Bibcode:1996JBAA..106...11G 
  14. ^ Mauron, N.; Caux, E. (November 1992), "K I/Na I scattering observations in circumstellar envelopes - Alpha(1) Herculis, Omicron Ceti, TX PISCIUM and Beta Pegasi", Astronomy and Astrophysics, 265 (2): 711–725, Bibcode:1992A&A...265..711M . Solar Radius = 0.0046491 AU.

Coordinates: Sky map 23h 03m 46.458s, +28° 04′ 58.04″