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
Distance204 ± 2 ly
(62.7 ± 0.7 pc)
Mass3.22[6] M
Radius4.03 ± 0.22[7] R
Luminosity224[6] L
Surface gravity (log g)3.67 ± 0.05[7] cgs
Temperature11,190 ± 55[7] K
Metallicity [Fe/H]+0.06[6] dex
Rotational velocity (v sin i)140[8]–210[9] km/s
Age120[9] Myr
Other designations
Homam, 42 Peg, BD+10° 4797, FK5 855, HD 214923, HIP 112029, HR 8634, SAO 108103.[10]
Database references

Zeta Pegasi (ζ Pegasi, abbreviated Zeta Peg, ζ Peg), formally named Homam /ˈhmæm/,[11][12] is a single[13] star in the northern constellation of Pegasus. 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 the Sun.[1]


ζ Pegasi (Latinised to Zeta Pegasi) is the star's Bayer designation.

It bore the traditional name Homam, meaning "Man of High Spirit" or "Lucky Star of High Minded". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalogue and standardize proper names for stars; the WGSN approved the name Homam for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[12]

In Chinese, 雷電 (Léi Diàn), meaning Thunder and Lightning, refers to an asterism consisting ζ Pegasi, ξ Pegasi, σ Pegasi, 55 Pegasi, 66 Pegasi and 70 Pegasi.[15] Consequently, the Chinese name for ζ Pegasi itself is 雷電一 (Léi Diàn yī), "the First Star of Thunder and Lightning".[16]


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.[7] 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[9] million years old and is rotating rapidly with a projected rotational velocity in the range of 140[8]–210[9] km s−1. The effective temperature of its outer envelope is around 11,190 K,[7] giving it the characteristic blue-white glow of a B-type star.[17]

Zeta Pegasi has been examined for infrared excess that may indicate the presence of circumstellar matter, but none was found;[18] 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.[18]


  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", Publications of the Department of Astronomy University of Chile, 1: 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", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg, 35 (35): 1, Bibcode:1999VeARI..35....1W
  6. ^ a b c Challouf, M.; et al. (2014), "Improving the surface brightness-color relation for early-type stars using optical interferometry⋆", Astronomy & Astrophysics, 570: A104, arXiv:1409.1351, Bibcode:2014A&A...570A.104C, doi:10.1051/0004-6361/201423772.
  7. ^ 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
  8. ^ 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
  9. ^ 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, CiteSeerX, doi:10.1086/426937
  10. ^ "zet Peg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-03-01.
  11. ^ 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.
  12. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016.
  13. ^ 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, CiteSeerX, doi:10.1086/510335
  14. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  15. ^ (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.
  16. ^ (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.
  17. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16
  18. ^ 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.