ALPHA CAE (Alpha Caeli). Of the 38 recognized modern constellations, those invented between about 1600 and 1800, Caelum, the Engraving Tool, is among the dimmest, the figure (which hardly looks its name) lying southwest of Columba, the Dove, a much finer pattern. Consistent with its name, Alpha Caeli (no proper name) is Caelum's brightest star, though not by much. At the low-brightness edge of fourth magnitude (4.46), it just beats Beta Caeli by a tenth of a magnitude. Dim as it is, however, the star has its draw. A double star, it consists of a somewhat solar-like class F (F2) dwarf coupled with a much fainter class M (M0.5) dwarf at the top edge of thirteenth magnitude (12.5), the dimness and separation of 6 seconds of arc making it a very difficult observation for the small telescope. Fairly nearby, 66 light years away, the 7100 Kelvin brighter F star shines with the light of 5.2 Suns, the radius only 1.5 times solar. Rotating with an equatorial speed of at least 52 kilometers per second, the star spins with a period of at most 1.4 days, much less than the Sun and typical of the hotter F stars that lie near (or hotter than) the so-called "rotation break," that divides slower rotating stars like the Sun from the faster rotating hotter ones. Though this star -- Alpha Caeli A -- has a mass of only 1.5 solar, it is much greater than that of the companion, Alpha Caeli B, which weighs in at but 0.3 solar. The low mass gives "B" a miserable luminosity of only a percent that of the Sun, this red dwarf having a surface temperature only 3800 Kelvin. Both temperatures are averages for stars of these classes, Alpha Cae so neglected that they have never actually been measured. Alpha Caeli B makes up for that by being a "flare star," one that (much like Proxima Centauri) can unpredictably brighten by a magnitude or more as a result of the release of magnetic energy. Alpha Caeli A may be a subtly-varying " Delta Scuti star" rather like much brighter Caph (Beta Cassiopeiae). The separation of Alpha Caeli A and B is not really known. They were 3 seconds of arc apart in 1896, 6.3 seconds in 1933, and the binary has not been visited since! Assuming 6.3, the two are at least 1000 Astronomical Units apart, and take at least 130 years to orbit each other. From B, A would shine 360 times brighter than our full Moon, while from A, B would glow redly with the light of over 100 of our Venuses.
Written by Jim Kaler. Return to STARS.