41 ARI (41 Arietis). Poor 41. In spite of it being the third brightest star (just over the line into fourth magnitude, 3.63) in its famous Zodiacal constellation, Aries (the Ram), not only has it no proper name, it even carries no Bayer Greek letter, the "41" a Flamsteed number. The most likely reason is the odd position of the star, which lies far to the east of the little triangle that represents the horns of the fabled Ram. 41 Ari, however, does have the distinction of being the brightest star within a small set of four that outline an even smaller triangle that hovers over the back of Aries and that represents the obsolete constellation of Musca Borealis, the "Northern Fly." Such defunct constellations abound, and many had good runs in various star atlases. The Fly, however, was finally swatted in the early twentieth century when the current 88 constellations were formally adopted. (Musca Australis, now known just as "Musca," still flits.) The small figure, easily found, serves nicely to represent the large set of modern constellations that are no longer recognized. Physically, 41 Ari is a rather hot blue-white class B (B8) dwarf star with a surface temperature estimated at around 12,000 Kelvin (no actual measures exist) that lies 160 light years away and that radiates 126 times as much energy as the Sun, from which we deduce a mass of around 3.2 solar, the star somewhere midway along its hydrogen-fusing 300 million year lifetime. Like most class B stars, 41 Ari is a fast rotator, spinning with an equatorial speed of at least 180 kilometers per second, 90 times faster than the Sun, which, given its radius of 2.6 times solar, translates into a rotation period of at most 17 hours. A host of lesser stars flock around 41, making it seem to be a multiple star. All but one, however, are line-of-sight accidents. The remaining one, a true companion, detected by both spectroscopy and interferometry (but about which nothing is known), lies only 0.2 seconds of arc from 41 itself. Orbiting perhaps 15 AU from 41, the companion would take some 30 years to make a full orbit. Though listed as "variable," modern observations suggest great stability, enough so that 41 Arietis could be used a standard against which to test real variables.
Written by Jim Kaler. Return to STARS.