Beta Pegasi

Red giant star in the constellation Pegasus From Wikipedia, the free encyclopedia

Beta Pegasi

Beta Pegasi (β Pegasi, abbreviated Beta Peg, β Peg), formally named Scheat /ˈʃæt/,[12][13] 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,[14] a prominent rectangular asterism.

Quick Facts Observation data Epoch J2000 Equinox J2000, Constellation ...
Beta Pegasi
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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)[1]
Absolute magnitude (MV)−1.41[7]
Details
Mass1.7±0.3[8] M
Radius109±7[9] R
Luminosity1,644[8][a] L
Surface gravity (log g)1.20[10] cgs
Temperature3,606[8] K
Metallicity [Fe/H]−0.11[10] dex
Rotational velocity (v sin i)9.7[11] km/s
Other designations
Scheat, 53 Pegasi, HR 8775, BD+27°4480, HD 217906, SAO 90981, FK5 870, HIP 113881[4]
Database references
SIMBADdata
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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.[14] In 2016, the International Astronomical Union organised a Working Group on Star Names (WGSN)[15] to catalog and standardise proper names for stars. The WGSN's first bulletin of July 2016[16] 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[13]).

In Chinese, 室宿 (Shì Xiù), meaning Encampment, refers to an asterism consisting β Pegasi and α Pegasi.[17] Consequently, the Chinese name for β Pegasi itself is 室宿二 (Shì Xiù èr), "the Second Star of Encampment".[18]

Distance and properties

Summarize
Perspective
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A light curve for Beta Pegasi, plotted from Hipparcos data[19]

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 109 times as large,[9] 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.[20] The photosphere is sufficiently cool for molecules of titanium oxide to form.[21]

Johann Friedrich Julius Schmidt discovered that Beta Pegasi is a variable star, in 1847.[22] 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).[23]

Notes

  1. Calculated from bolometric magnitude in the equation 100.4(4.74-Mbol), where "Mbol" is the bolometric magnitude.

References

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