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AUVA

(Delta Virginis). The proper name, which from Arabic means "the Barker," does not really belong to the star, but to a group of stars in Virgo to the west of Spica that represent a kennel for dogs: Beta, Gamma, Epsilon, Eta, and Delta. But since all but poor Delta already have other proper names (the first four respectively Zavijava, Porrima, Vindemiatrix, and Zaniah), the name of the group rather naturally, though informally, falls onto Delta itself. Auva is one of the sky's rather few naked-eye class M red giants, and a coolish one (class M3) at that. Appropriately ranking in brightness (though named "Delta" more for position), the star shines toward the faint end of third magnitude (3.38) from a distance of 202 light years. With a temperature of only 3720 Kelvin, Auva radiates much of its light in the infrared where it cannot be seen with the eye. When that is taken into account, the star is calculated to be 630 times more luminous than the Sun, which with temperature gives it a radius 61 times solar, or a quarter of the radius of the Earth's orbit. The star's measured angular diameter of 0.0098 seconds of arc gives a similar value of 65 solar radii, showing that all the measures are closely self-consistent. Though Auva is certainly evolved and dying, it is not possible to delineate its exact nature. The star, with a mass near 1.5 to 2 times that of the Sun, is near the tip of the so-called "red giant branch" or stars (where lower mass stars reach their maximum brightness as their dead helium cores turn on to fuse helium to carbon). Auva could be brightening with a dead helium core, it could be starting to dim some as it fuses its newly-awakened helium, or it could even be brightening with a dead carbon core. Auva may or may not have a companion. An 11th magnitude star lies 80 seconds of arc away, but its distance and motion remain unmeasured. If it is a true companion, its brightness suggests that it is a class K dwarf that lies at least 5000 Astronomical Units from Auva proper and takes over 200,000 years to orbit. If true neighbors, from Auva, the little one would shine over twice as bright as our Venus, while from the companion, reddish Auva would appear four times as bright as our full Moon. On the other hand, the alignment of the two may be mere coincidence. It has not been important enough to anyone to find out.