Location of β Pegasi (circled) | |
Observation data Epoch J2000 Equinox J2000 | |
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Constellation | Pegasus |
Right ascension | 23 03 46.45746 |
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 | 109±7 R☉ |
Luminosity | 1,644 L☉ |
Surface gravity (log g) | 1.20 cgs |
Temperature | 3,606 K |
Metallicity | −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/, 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, 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. In 2016, the International Astronomical Union organised a Working Group on Star Names (WGSN) to catalog and standardise proper names for stars. The WGSN's first bulletin of July 2016 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).
In Chinese, 室宿 (Shì Xiù), meaning Encampment, refers to an asterism consisting β Pegasi and α Pegasi. Consequently, the Chinese name for β Pegasi itself is 室宿二 (Shì Xiù èr), "the Second Star of Encampment".
Distance and properties
Based upon parallax measurements, Beta Pegasi is located about 196 light-years (60 parsecs) from the Sun. 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, which indicates the spectrum has characteristics partway between a bright giant and a giant star. It has expanded until it is 109 times as large, and has a total luminosity of 1,640 times that of the Sun. The effective temperature of the star's outer envelope is about 3,600 K, giving the star the characteristic orange-red hue of an M-type star. The photosphere is sufficiently cool for molecules of titanium oxide to form.
Johann Friedrich Julius Schmidt discovered that Beta Pegasi is a variable star, in 1847. Beta Pegasi is a semi-regular variable with a period of 43.3 days and a brightness that varies from magnitude +2.31 to +2.74 (averaging 2.42). It is losing mass at a rate at or below 10 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).
Notes
- Calculated from bolometric magnitude in the equation 10, where "Mbol" is the bolometric magnitude.
References
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- ^ 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.
- ^ "Query= bet Peg", General Catalogue of Variable Stars, Centre de Données astronomiques de Strasbourg, retrieved 2010-01-05
- ^ "V* bet Peg -- Pulsating variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2010-01-05
- ^ 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
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- ^ 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 (3): 2957–2967. arXiv:1507.01517. Bibcode:2015MNRAS.451.2957H. doi:10.1093/mnras/stv1141. ISSN 0035-8711.
- ^ Arroyo-Torres, B.; et al. (June 2014). "VLTI/AMBER observations of cold giant stars: atmospheric structures and fundamental parameters". Astronomy & Astrophysics. 566: 11. arXiv:1404.7384. Bibcode:2014A&A...566A..88A. doi:10.1051/0004-6361/201323264. S2CID 16778588. A88.
{{cite journal}}
: CS1 maint: postscript (link) - ^ 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
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- 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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