Zeta Pegasi

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

Location of ζ Pegasi (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Pegasus
Right ascension 22h 41m 27.72072s[1]
Declination +10° 49′ 52.9079″[1]
Apparent magnitude (V) +3.414[2]
Spectral type B8 V[3]
U−B color index –0.181[2]
B−V color index –0.088[2]
Variable type SPB[4]
Radial velocity (Rv) +7.0[5] km/s
Proper motion (μ) RA: +77.22[1] mas/yr
Dec.: –11.38[1] mas/yr
Parallax (π) 15.96 ± 0.19[1] mas
Distance 204 ± 2 ly
(62.7 ± 0.7 pc)
Radius 4.03 ± 0.22[6] R
Surface gravity (log g) 3.67 ± 0.05[6] cgs
Temperature 11,190 ± 55[6] K
Rotational velocity (v sin i) 140[7]–210[8] km/s
Age 120[8] Myr
Other designations
Homam, 42 Peg, BD+10 4797. FK5 855, HD 214923, HIP 112029, HR 8634, SAO 108103.[9]

Zeta Pegasi (ζ Peg) is a single[10] star in the northern constellation of Pegasus. It has the traditional name, Homam, meaning "Man of High Spirit" or "Lucky Star of High Minded". With an apparent visual magnitude of +3.4,[2] this star is bright enough to be seen with the naked eye and is one of the brighter members of Pegasus. Parallax measurements place it at a distance of around 204 light-years (63 parsecs) from Earth.[1]

This star has a stellar classification of B8 V,[3] which identifies it as a large B-type main sequence star that is generating energy through the nuclear fusion of hydrogen at its core. The radius of this star is about four times that of the Sun.[6] It is a slowly pulsating B star that varies slightly in luminosity with a period of 22.952 ± 0.804 hours, completing 1.04566 cycles per day.[4] Zeta Pegasi is about 120[8] million years old and is rotating rapidly with a projected rotational velocity in the range of 140[7]–210[8] km s−1. The effective temperature of its outer envelope is around 11,190 K,[6] giving it the characteristic blue-white glow of a B-type star.[11]

Zeta Pegasi has been examined for infrared excess that may indicate the presence of circumstellar matter, but none was found.[12] This star does have two optical companions. The first is a magnitude 11.6 star at an angular separation of 68 arcseconds along a position angle of 139°, as of 1997.[4] The second is an 11th magnitude star at a separation of 177 arcseconds with a position angle of 5°.[5] Zeta Pegasi is not known to be a member of a stellar association.[12]


  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 Gutierrez-Moreno, Adelina et al. (1966), A System of photometric standards 1, Publicaciones Universidad de Chile, Department de Astronomy, pp. 1–17, Bibcode:1966PDAUC...1....1G 
  3. ^ a b Palmer, D. R. et al. (1968), "The radial velocities spectral types and projected rotational velocities of 633 bright northern A stars", Royal Observatory Bulletin 135: 385, Bibcode:1968RGOB..135..385P 
  4. ^ a b c Goebel, John H. (May 2007), "Gravity Probe B Photometry and Observations of ζ Pegasi: An SPB Variable Star", The Publications of the Astronomical Society of the Pacific 119 (855): 483–493, Bibcode:2007PASP..119..483G, doi:10.1086/518618 
  5. ^ a b Wielen, R. et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W 
  6. ^ a b c d e Fitzpatrick, E. L.; Massa, D. (March 2005), "Determining the Physical Properties of the B Stars. II. Calibration of Synthetic Photometry", The Astronomical Journal 129 (3): 1642–1662, arXiv:astro-ph/0412542, Bibcode:2005AJ....129.1642F, doi:10.1086/427855 
  7. ^ a b Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590 
  8. ^ a b c d Rieke, G. H. et al. (February 2005), "Decay of Planetary Debris Disks", The Astrophysical Journal 620 (2): 1010–1026, Bibcode:2005ApJ...620.1010R, doi:10.1086/426937 
  9. ^ "zet Peg -- Star in double system", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-03-01 
  10. ^ Roberts, Lewis C., Jr.; Turner, Nils H.; ten Brummelaar, Theo A. (February 2007), "Adaptive Optics Photometry and Astrometry of Binary Stars. II. A Multiplicity Survey of B Stars", The Astronomical Journal 133 (2): 545–552, Bibcode:2007AJ....133..545R, doi:10.1086/510335 
  11. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16 
  12. ^ a b Su, K. Y. L. et al. (December 2006). "Debris Disk Evolution around A Stars". The Astrophysical Journal 653 (1): 675–689. arXiv:astro-ph/0608563. Bibcode:2006ApJ...653..675S. doi:10.1086/508649.