Alpha Pegasi - Markab

At magnitude 2.49, Alpha Pegasi is the third brightest star in the constellation Pegasus, despite its α designation. It lies at the southwestern corner of the the asterism known as the Great Square of Pegasus, which it makes along with β Peg (Scheat), γ Peg (Algenib), and α And (Alpheratz). α Peg has the traditional name Markab (or Marchab), which comes from the Arabic word for "saddle" (of the horse). Markab may also be a mistranscription of Mankib, from an Arabic phrase "Mankib al-Faras", meaning "the shoulder of the Horse."

Properties

Markab itself is a relatively hot class B9 III giant, similar to Regulus in Leo. Its distance of 140 light years implies a total luminosity of 205 suns, including ultraviolet radiation. With the star's temperature (10500 K), this yields a radius 4.3 times solar. Just a hair over three solar masses, and still spinning fairly rapidly with a rotation period under 1.5 days, Markab has just begun to evolve to a red giant. It is very close to ceasing hydrogen fusion in its core. It will expand, slow its rotation, and become a much cooler orange giant, many times its current luminosity, then finally die finally as a massive white dwarf.

There is some evidence from Markab's motion for a small stellar companion. Markab is noted for its normality, as it provides a standard against which to measure other stars.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]