Zeta Pegasi is a star of magnitude 3.40 in Pegasus, the Winged Horse. Its traditional name, Homam, originally belonged to a pair of stars, Zeta and Xi Pegasi, known together to the ancient Arabs as the "lucky stars of the hero". The name then devolved specifically to ζ Peg, leaving ξ Peg nameless.
Properties
Homam is a class B8 V star with a temperature of 11200 K that lies 209 light years away. From that, it has a luminosity of 227 suns, and a radius 4.0 times solar. The star's luminosity and temperature imply a mass between 3.3 and 3.5 suns. The star is finishing up core hydrogen fusion, with an age around 260 million years.
Like many young class B stars, ζ Peg is a fast rotator, spinning with an equatorial speed of at least 140 km/sec, which gives it a rotation period under 1.4 days (as opposed to the Sun's 25 day period). One classification lists ζ Peg as an emission star, suggesting an equatorial gas disk related to the high rotation. Typical of local class B stars, ζ Peg's metal abundance compared to hydrogen is a bit low, some 40% of the Sun's. ζ Peg also seems to be a "slowly pulsating B star", varying by merely 0.00049 magnitudes over a 22.95 hour period.
Companions
ζ Peg appears to have two companions. ζ Peg B is a magnitude 11.6 star at a current separation of 59". Given that in 1879 the separation was 64", this companion is clearly a line-of-sight coincidence; the change is much too great to be orbital motion.
Eleventh magnitude ζ Peg C seems real, however, since its separation has stayed constant at 177" over more than a century. If a real companion at the same distance as ζ Peg A, then ζ Peg C is a K6 V dwarf with a mass of around 0.6 suns. At a minimum distance of 11,000 AU, its orbital period would be at least 600,000 years.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]