Beta Pegasi

Beta Pegasi (β Pegasi, abbreviated Beta Peg, β Peg), formally named Scheat /ˈʃiːæt/,[11][12] is a red giant star and the second-brightest star (after Epsilon Pegasi) in the constellation of Pegasus. It forms the upper right corner of the Great Square of Pegasus,[13] a prominent rectangular asterism.

"Scheat" redirects here. For the star in Aquarius, see Delta Aquarii.
Beta Pegasi
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]
Characteristics
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]
Astrometry
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 mas[1]
Distance196 ± 2 ly
(60.1 ± 0.5 pc)
Absolute magnitude (MV)−1.41[7]
Details
Mass2.1[8] M☉
Radius95 R☉
Surface gravity (log g)1.20[9] cgs
Temperature3,689[9] K
Metallicity [Fe/H]−0.11[9] dex
Rotational velocity (v sin i)9.7[10] km/s
Other designations
Scheat, 53 Pegasi, HR 8775, BD+27°4480, HD 217906, SAO 90981, FK5 870, HIP 113881[4]
Database references
SIMBADdata

Nomenclature

β Pegasi (Latinised to Beta Pegasi) is the star's Bayer designation.

It bore the traditional name of Scheat, a name that had also been used for Delta Aquarii. The name was derived from the Arabic Al Sā'id "the upper arm", or from Sa'd.[13] In 2016, the International Astronomical Union organised a Working Group on Star Names (WGSN)[14] to catalog and standardise proper names for stars. The WGSN's first bulletin of July 2016[15] included a table of the first two batches of names approved by the WGSN; which included Scheat for this star (the name Skat was later approved for Delta Aquarii[12]).

In Chinese, 室宿 (Shì Xiù), meaning Encampment, refers to an asterism consisting β Pegasi and α Pegasi.[16] Consequently, the Chinese name for β Pegasi itself is 室宿二 (Shì Xiù èr), "the Second Star of Encampment".[17]

Distance and properties
A light curve for Beta Pegasi, plotted from Hipparcos data[18]

Based upon parallax measurements, Beta Pegasi is located about 196 light-years (60 parsecs) from the Sun.[1] It is unusual among bright stars in having a relatively cool surface temperature compared to stars like the Sun. 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 1,500 times that of the Sun. 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.[19] The photosphere is sufficiently cool for molecules of titanium oxide to form.[20]

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 (averaging 2.42).[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).[21]

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, S2CID 18759600
  2. 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. "Query= bet Peg", General Catalogue of Variable Stars, Centre de Données astronomiques de Strasbourg, retrieved 2010-01-05
  4. "V* bet Peg -- Pulsating variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2010-01-05
  5. 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:0908.3228, Bibcode:2009MNRAS.400.1945T, doi:10.1111/j.1365-2966.2009.15588.x, S2CID 15358380
  6. Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Washington, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W
  7. Huang, W.; et al. (2012), "A catalogue of Paschen-line profiles in standard stars", Astronomy & Astrophysics, 547: A62, arXiv:1210.7893, Bibcode:2012A&A...547A..62H, doi:10.1051/0004-6361/201219804, S2CID 119286159.
  8. Tsuji, Takashi (May 2007), Kupka, F.; Roxburgh, I.; Chan, K. (eds.), "Isotopic abundances of Carbon and Oxygen in Oxygen-rich giant stars", Convection in Astrophysics, Proceedings of the International Astronomical Union, 2 (S239): 307–310, arXiv:astro-ph/0610180, Bibcode:2007IAUS..239..307T, doi:10.1017/S1743921307000622, S2CID 119362842
  9. 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:0712.1370, Bibcode:2008A&A...480...91S, doi:10.1051/0004-6361:20078788, S2CID 16602121
  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, S2CID 121883397
  11. Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  12. "IAU Catalog of Star Names". Retrieved 28 July 2016.
  13. Allen, Richard Hinckley (1899), Star Names: Their Lore and Meaning, New York, NY: Dover Publications Inc., p. 325, ISBN 0-486-21079-0
  14. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  15. "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  16. (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  17. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  18. "Light Curve", Hipparcos ESA, ESA, retrieved 21 September 2022.
  19. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-18, retrieved 2012-01-16
  20. 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
  21. 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.
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