Beta Canis Minoris - Gomeisa

At magnitude 2.90, β CMi is the second-brightest star in Canis Minor, the smaller of Orion's two hunting dogs. It is noted mostly for its proximity to bright Procyon.

The star's traditional name, Gomeisa, comes from an Arabic term that means "the little bleary-eyed one." The term was transferred from Canis Minor's Procyon (which now carries a Greek name), and originally referred to Procyon as a weeping sister of Sirius, stranded from her by the "river" of the Milky Way.

Properties

Gomeisa is in fact far more luminous than Procyon, rendered apparently fainter only by its larger distance of 170 light years - 15 times Procyon's distance. Gomeisa is a blue-white class B8 V main sequence star with a temperature of 11,500 K, fusing hydrogen into helium in its core. However, with a mass over three times the Sun's, Gomeisa is far more luminous, shining as brightly as 250 suns. Its diameter has been directly measured to be four times larger than the Sun's.

Like most class B stars, Gomeisa is a fast rotator, spinning at its equator with a speed of at least 250 km/sec, giving the star a rotation period of only about one day - 25 times faster than the Sun. It is rotating so quickly that it is surrounded by a disk of radiation-emitting matter, making Gomeisa a "B-emission" star like Gamma Cassiopeiae. It is also slightly variable, and belongs to the γ Cas category of variable stars. Gomeisa is also surrounded by a thin cloud of dusty interstellar gas that it helps to heat.

β CMi is single, like the Sun, and shows no evidence of any companion.

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