RIJL AL AWWA (Mu Virginis). Many constellations are hosts to informal figures, to various "asterisms." Some, like the Big and Little Dippers (which belong to Ursa Major and Minor), Orion's Belt, and Pegasus's Great Square, are famed and beloved. Many, however, particularly those belonging to the ancient Arabic culture that has played such a strong role in the history of our constellations and star names, are remarkably obscure. To Virgo belongs one of the latter, one made of the five stars of the Arabs' "Awwa," or "Barker." To the northwest of Spica, Al Awwa relates to a "Kennel," and consists of Porrima (Gamma Virginis), Vindemiatrix (Epsilon), Delta Virginis, Zaniah (Eta), and Zavijava (Beta). Almost as an afterthought, fourth magnitude (3.88) Mu Virginis (way on the other side of Spica in eastern Virgo) gets included as "Rijl al Awwa," the "Foot of the Barker." While serving as a window to another long-gone culture, it is known today only by its Greek letter name, not to mention also by a long list of catalogue names. All that said, the star itself, while formally listed as a class F (F2) giant, actually has all the characteristics of a mid-temperature (6730 Kelvin) hydrogen-fusing dwarf, and quite a close one too, just 60 light years away with an uncertainty of less than 1 l-y. Mu's luminosity (the vast majority in the visual spectrum, where we can actually see it) of 7.5 times that of the Sun leads to a radius of 2.0 times solar (close to the value of 2.1 solar radii used as a secondary calibrator for interferometry measures). A projected equatorial rotation velocity of 54 kilometers per second (27 times that of the Sun, but still not all that high) yields a rotation period of under 1.9 days. Theory then gives us a mass of 1.55 Suns and clearly shows Mu Virginis to be a dwarf about in the middle of its hydrogen-fusing lifetime of 2.5 billion years. Such "misdiagnoses," warmer dwarfs classified as giants, are not all that uncommon since for such stars the differences in the spectra are not all that great. Later classification indeed put it into the ranks of true dwarfs. The star's metal content relative to the Sun is slightly low, while the velocity is a bit high (about double the average). There is some indication that Mu has a spectroscopic companion with a roughly-determined period of 358 days, which given low mass would imply a separation of around three-quarters of an Astronomical Unit, but it has never been confirmed and may well not exist. So far as we know, there are no planets, nor even any indication of a surrounding dusty disk that might imply a planetary system, Mu Vir then fading into the obscurity implied by its even more obscure proper name.
Written by Jim Kaler 5/06/11. Return to STARS.