Beta Pegasi

Beta Pegasi
	Location of β Pegasi (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Pegasus
Right ascension	23h 03m 46.45746s
Declination	+28° 04′ 58.0336″
Apparent magnitude (V)	2.42 (2.31 – 2.74)
Characteristics
Spectral type	M2.5II–IIIe
U−B color index	+1.96
B−V color index	+1.67
Variable type	Semi-regular
Astrometry
Radial velocity (Rv)	+8.7 km/s
Proper motion (μ)	RA: +187.65 mas/yr ; Dec.: +136.93 mas/yr
Parallax (π)	16.64 ± 0.15 mas
Distance	196 ± 2 ly ; (60.1 ± 0.5 pc)
Absolute magnitude (MV)	−1.41
Details
Mass	1.7±0.3 M☉
Radius	104 R☉
Luminosity	1,644 L☉
Surface gravity (log g)	1.20 cgs
Temperature	3,606 K
Metallicity [Fe/H]	−0.11 dex
Rotational velocity (v sin i)	9.7 km/s
Other designations
	Scheat, 53 Pegasi, HR 8775, BD+27°4480, HD 217906, SAO 90981, FK5 870, HIP 113881
Database references
SIMBAD	data

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.

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 104 times as large, and has a total luminosity of 1,640 times that of the Sun.^[8] The effective temperature of the star's outer envelope is about 3,600 K,^[8] 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]

Notes

^ Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:
${\sqrt {{\biggl (}{\frac {5,772}{3,606}}{\biggr )}^{4}\cdot 1,644}}=103.9\ R_{\odot }$ .
^ Calculated from bolometric magnitude in the equation 10^{0.4(4.74-M_bol)}, where "M_bol" is the bolometric magnitude.

References

^ ^a ^b ^c ^d ^e ^f ^g 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
^ ^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.
^ ^a ^b "Query= bet Peg", General Catalogue of Variable Stars, Centre de Données astronomiques de Strasbourg, retrieved 2010-01-05
^ ^a ^b ^c "V* bet Peg -- Pulsating variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2010-01-05
^ ^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:0908.3228, Bibcode:2009MNRAS.400.1945T, doi:10.1111/j.1365-2966.2009.15588.x, S2CID 15358380
^ Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Washington, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W
^ 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.
^ ^a ^b ^c ^d ^e ^f Halabi, Ghina M.; Eid, Mounib El (2015-08-01). "Exploring masses and CNO surface abundances of red giant stars". Monthly Notices of the Royal Astronomical Society. 451: 2957–2967. arXiv:1507.01517. doi:10.1093/mnras/stv1141. ISSN 0035-8711.
^ ^a ^b 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
^ 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
^ 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.
^ ^a ^b "IAU Catalog of Star Names". Retrieved 28 July 2016.
^ ^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
^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
^ (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.
^ (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.
^ "Light Curve", Hipparcos ESA, ESA, retrieved 21 September 2022.
^ "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
^ 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
^ 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.