GOMEISA (Beta Canis Minoris).
Carrying seemingly one of the odder star names, Gomeisa
(hard "G", the "ei" said as long "a" or short "i") comes from an
Arabic term that means "the little bleary-eyed one." Though the
Beta star of Canis Minor,
the smaller of Orion's two hunting dogs,
the name has no canine significance. The term was instead
transferred from Canis Minor's Procyon,
which now carries a Greek
name, and originally referred to the brighter star as a weeping
sister left behind when Sirius and Canopus ran to the south to save their
lives. Star names are nothing if not convoluted, even inscrutable.
At mid-third magnitude (2.90), the star is notable more for its proximity
to bright Procyon. Yet it is by far the
more glorious star, rendered apparently fainter only by its larger
distance of 170 light years, 15 times Procyon's distance. Gomeisa
is a blue-white class B (B8) star with a temperature of 11,500 Kelvin,
just a bit warmer than Orion's Rigel.
Unlike Rigel, Gomeisa is a main-sequence "dwarf" that, like the
Sun, is fusing hydrogen into helium in its core. Like the
Sun it
is also single, showing no evidence for any companion. However,
with a mass over three times the Sun's, Gomeisa radiates far more
furiously, shining with 250 solar luminosities, the star directly
measured to be four times larger than the Sun. Like most class B
stars (which range between about 10,000 and 30,000 Kelvin), Gomeisa
is a fast rotator, spinning at its equator with a speed of at least
250 kilometers per second, 125 times the solar rotation speed,
giving the star a rotation period of only about one day. Since we
may be looking more at the star's pole than at its equator, it may
be spinning much faster, and indeed is rotating so quickly that it
is surrounded by a disk of matter that emits radiation, rendering
Gomeisa a "B-emission" star rather like
Gamma Cassiopeiae and
Alcyone.
Like these two, Gomeisa is distinguished by having the
size of its disk directly measured, the disk's diameter almost four
times larger than the star. Like quite a number of hot stars
(including Adhara, Nunki, and many others), Gomeisa is also
surrounded by a thin cloud of dusty interstellar gas that it helps
to heat. (Thanks to Jason Pero, who helped research this star.)