Mu Pegasi

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Mu Pegasi
Diagram showing star positions and boundaries of the Pegasus constellation and its surroundings
Cercle rouge 100%.svg

Location of μ Pegasi (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Pegasus
Right ascension 22h 50m 00.19315s[1]
Declination +24° 36′ 05.6984″[1]
Apparent magnitude (V) 3.514[2]
Spectral type G8 III[3]
U−B color index +0.674[2]
B−V color index +0.932[2]
Radial velocity (Rv) +13.54 ± 0.20[4] km/s
Proper motion (μ) RA: +144.70[1] mas/yr
Dec.: –41.87[1] mas/yr
Parallax (π) 30.74 ± 0.27[1] mas
Distance 106.1 ± 0.9 ly
(32.5 ± 0.3 pc)
Absolute magnitude (MV) 0.432[5]
Mass 1.3[6] M
Radius 9.6 ± 0.4[7] R
Surface gravity (log g) 2.50[3] cgs
Temperature 4,950[3] K
Metallicity [Fe/H] –0.03[3] dex
Rotational velocity (v sin i) 4.0[8] km/s
Other designations
μ Peg, 48 Peg, BD+23 4615, FK5 862, GJ 4298, HD 216131, HIP 112748, HR 8684, SAO 90816.[9]

Mu Pegasi (μ Peg, μ Pegasi) is a star in the northern constellation of Pegasus. It has the traditional name Sadalbari, which derives from the Arabic term for "luck star of the splendid one".[10] The apparent visual magnitude of this star is 3.5,[2] which is bright enough to be seen with the naked eye even on a moonlit night. The distance to this star can be determined with parallax measurements, which yields a value of 106.1 light-years (32.5 parsecs).[1]

The spectrum of this star matches a stellar classification of G8 III.[3] The luminosity class of 'III' means that it has exhausted the hydrogen fuel at its core and evolved into a giant star. It is slightly more massive than the Sun, but has expanded to nearly ten times the Sun's radius.[7] (Mishenina et al. (2006) list it with an estimated 2.7 times the mass of the Sun.[5]) The effective temperature of the outer atmosphere is about 4,950 K,[3] which is cooler than the Sun and gives it the yellow hue of a G-type star.[11][12] The abundance of elements other than hydrogen and helium, what astronomers term the metallicity, is similar to the abundance in the Sun.[3]


  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:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d Jennens, P. A.; Helfer, H. L. (September 1975), A new photometric metal abundance and luminosity calibration for field G and K giants., Monthly Notices of the Royal Astronomical Society 172: 667–679, Bibcode:1975MNRAS.172..667J 
  3. ^ a b c d e f g Frasca, A. et al. (December 2009), REM near-IR and optical photometric monitoring of pre-main sequence stars in Orion. Rotation periods and starspot parameters, Astronomy and Astrophysics 508 (3): 1313–1330, Bibcode:2009A&A...508.1313F, doi:10.1051/0004-6361/200913327 
  4. ^ Famaey, B. et al. (January 2005), Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters, Astronomy and Astrophysics 430 (1): 165–186, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272 
  5. ^ a b Mishenina, T. V. et al. (September 2006), Elemental abundances in the atmosphere of clump giants, Astronomy and Astrophysics 456 (3): 1109–1120, arXiv:astro-ph/0605615, Bibcode:2006A&A...456.1109M, doi:10.1051/0004-6361:20065141 
  6. ^ Smith, G. (November 1998), Stellar atmospheric parameters for the giant stars MU Pegasi and lambda Pegasi, Astronomy and Astrophysics 339: 531–536, Bibcode:1998A&A...339..531S 
  7. ^ a b Nordgren, Tyler E. et al. (December 1999), Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer, The Astronomical Journal 118 (6): 3032–3038, Bibcode:1999AJ....118.3032N, doi:10.1086/301114 
  8. ^ 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 
  9. ^ 48 Peg -- High proper-motion Star, SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2012-01-28 
  10. ^ Allen, Richard Hinckley, (1963) [1899]. Star Names: Their Lore and Meaning (rep. ed.). New York, NY: Dover Publications Inc. pp. 328–29. ISBN 0-486-21079-0. 
  11. ^ The Colour of Stars, Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16 
  12. ^ Kaler, James B., SADALBARI (Lambda and Mu Pegasi), Stars (University of Illinois), retrieved 2012-01-28