MUHLIFAIN (Gamma Centauri). Lying in east-central Centaurus, the name Muhlifain refers to "two things" and to the "swearing of an oath," hardly appropriate for a Centaur. No wonder, as the name is not at all representative of the star, but was given by mistake, taken from a star all the way around the sky, Muliphein, the Gamma star in Canis Major. No one seems to know why, though such name- transference is rather common. Seen below 40 degrees north latitude, this star follows the order of the Greek alphabet, and is in fact the third brightest in the constellation. At mid-second magnitude (2.17) it is commonly ignored in favor of the constellation's pair of first magnitude stars, Rigil Kentaurus (Alpha Centauri) and Hadar (Beta). Muhlifain deserves more respect than it gets. Classed singly as a warm A (A1) subgiant, the telescope shows it to be a pair of identical white A stars (that are sometimes classed as A1 giants). At a distance of 130 light years, the twins are separated by under a second of arc, each shining with the light of 95 Suns from surfaces heated to about 9300 Kelvin. Luminosity and temperature indicate masses 2.8 times solar. Though close together, their mutual orbit has been well-mapped. They circuit each other every 84.5 years (coincidentally about the same as the period of Rigil Kent's pair) at an average distance of 37 Astronomical Units (just short of the distance between Pluto and the Sun), but in elliptical paths that take them as close as 8 Astronomical Units and as far apart as 67 AU. Under such conditions, no planetary systems seem likely. The orbit tells of stars with masses of 3.7 solar, greater than that derived from luminosity and temperature, suggesting that one or both stars may have a low mass orbiting companion (for which, however, there is no spectroscopic evidence). The stars are so close in character that they are evolving at the same time, producing rather a rather rare combination of two subgiants (stars that have either just given up their hydrogen fusion or are preparing to do so) that will produce a pair of giants -- and maybe even (as they lose mass together) a unique double planetary nebula as their outer envelopes flee into space before the twins turn into identical white dwarfs.
Written by Jim Kaler. Return to STARS.