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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 anArabic term that means "the little bleary-eyed one." Though theBeta star ofCanis Minor, the smaller ofOrion's two hunting dogs,the name has no canine significance. The term was insteadtransferred from Canis Minor'sProcyon, which now carries a Greekname, and originally referred to the brighter star as a weepingsister left behind whenSirius andCanopus ran to the south to save theirlives. Star names are nothing if not convoluted, even inscrutable. At mid-third magnitude (2.90), the star is notable more for its proximityto bright Procyon. Yet it is by far themore glorious star, rendered apparently fainter only by its largerdistance of 170 light years, 15 times Procyon's distance. Gomeisais a blue-white class B (B8) star with a temperature of 11,500 Kelvin,just a bit warmer than Orion'sRigel. Unlike Rigel, Gomeisa is a main-sequence "dwarf" that, like theSun, is fusing hydrogen into helium in its core. Like theSun itis also single, showing no evidence for any companion. However,with a mass over three times the Sun's, Gomeisa radiates far morefuriously, shining with 250 solar luminosities, the star directlymeasured to be four times larger than the Sun. Like most class Bstars (which range between about 10,000 and 30,000 Kelvin), Gomeisais a fast rotator, spinning at its equator with a speed of at least250 kilometers per second, 125 times the solar rotation speed,giving the star a rotation period of only about one day. Since wemay be looking more at the star's pole than at its equator, it maybe spinning much faster, and indeed is rotating so quickly that itis surrounded by a disk of matter that emits radiation, renderingGomeisa a "B-emission" star rather likeGamma Cassiopeiae andAlcyone. Like these two, Gomeisa is distinguished by having thesize of its disk directly measured, the disk's diameter almost fourtimes larger than the star. Like quite a number of hot stars(includingAdhara,Nunki, and many others), Gomeisa is alsosurrounded by a thin cloud of dusty interstellar gas that it helpsto heat. (Thanks to Jason Pero, who helped research this star.)
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