ALKALUROPS (Mu Bootis). The naming of stars sometimes seems random. Some bright stars within a constellation will carry no proper names, while other much fainter ones do (the classic case that of Gamma Cassiopeiae). In Bootes, the Herdsman, the Alpha, Beta, and Gamma stars carry the proper names Arcturus, Nekkar, and Seginus. Third magnitude Delta has none, but then we can reach all the way to fourth magnitude (4.31) Mu Bootis, which is called by the jaw-breaking name Alkalurops. Once we get away from the first magnitude stars, naming has more to do with position than brightness. "Alkalurops" actually derives from Greek, and means "club." But the original, going from Greek to Arabic to Latin to Greek to Latin and thence made to sound Arabic, came to mean "shepherd's staff," more fitting for the Herdsman. Alkalurops is a wonderful triple star. Lying 1.8 minutes of arc away from the star is a sixth (6.50) magnitude companion technically visible to the naked eye. The principal star, Alkalurops proper (Alkalurops A), is a mid-temperature (7195 Kelvin) class F(F0) dwarf. At a distance of 120 light years, it radiates 20 solar luminosities, which makes it too bright for its class, implying that it is either starting to evolve or that it too is double. The spectrum suggests an unresolved companion with a period near 300 days (making the system quadruple). The star may also be a subtle variable. The easily-visible companion (Alkalurops BC), however, is clearly double, and consists of a pair of sunlike (class G1) dwarf stars that average 1.5 seconds of arc apart. The seventh magnitude (6.98) brighter star (Alkalurops B) has double the solar luminosity, whereas the fainter seventh magnitude companion (Alkalurops C, 7.63) is almost a solar clone. The two orbit each other every 260 years at an average distance of 54 Astronomical Units (35 percent farther than Pluto is from the Sun). The smaller pair lies at least 4000 AU distant from two- solar mass (or so) Alkalurops A and takes at least 125,000 years to make a full circuit. From Alkalurops A, the BC pair would appear as a brilliant "double sun" (at that distance, however, starlike) 100 times or so brighter than our Venus, separated by up to a degree apart. Alkalurops A lies near a critical stellar transition point. Hotter stars fuse hydrogen to helium through the carbon cycle (in which carbon is used as a nuclear catalyst) rather than directly, have no circulating convective outer layers, and also tend to rotate much faster (Alkalurops spinning at least 40 times faster than the Sun).
Written by Jim Kaler. Return to STARS.