BETA EQU (Beta Equulei). Among the only reasons to tout this star is Bayer's Beta designation, as we try to accommodate all the Beta stars. As is fairly common, the constellation of Equuleus, the Little Horse, is dominated by the Alpha star, fourth magnitude Kitalpha, while Beta does not come up to par. Number two is Delta Equ, followed by Gamma, and then in fourth place, up comes fifth magnitude (5.16) Beta. If you thought (if anybody thinks to think it) that Beta Piscis Austrini was neglected, try this one, with a sad 27 professional references over the past century or so. On the surface, it's just another class A (A3) dwarf, yet one with its own small interest. At roughly 9000 Kelvin, Beta Equulei shines at us from a distance of 101 light years (give or take 3) with a luminosity of 75 times that of the Sun -- nice and bright for its class. That gives us a radius of 3.6 solar and (given an equatorial rotation velocity of at least 49 kilometers per second) a rotation period under four days. The mass falls between 2.4 and 2.5 times that of the Sun depending on the exact state of evolution, which in any case is near the end of the hydrogen-fusing line, really rendering the star a subgiant, the age about 600 million years. In spite of the pathetic number of references, Beta Equ has two things to recommend it. First, like Vega and Fomalhaut, it's surrounded by a dusty disk that by itself suggests planets (though none have been found). Second it has a swarm of faint (12th-14th magnitude) companions, Beta- B through E, whose separations range from 39 seconds of arc to 94 seconds away. All of them, however, are moving too fast relative to Beta-A, and are thus clearly just line-of-sight coincidences. Curiously the CD pair may indeed be a real binary, though little is known, and nobody seems to care -- in line with Beta Equulei proper.
Written by Jim Kaler 12/18/09. Return to STARS.