TANIA BOREALIS (Lambda Ursae Majoris). Three pairs of unrelated stars mark the feet of Ursa Major, the Great Bear. To the Arabs, they marked the "leaps of the gazelle," the first, second, and third leaps proceeding from east to west. Tania Borealis (Lambda Ursae Majoris) is the more northerly of the stars that make the "Second Leap," the name from a long phrase that means just that (plus the Latin for "northern"). The southern star of the pair is Tania Australis (Mu UMa), while the first leap is made by Alula Borealis and Australis (Nu and Xi), the third from Talitha (Iota) and Kappa UMa. Positioned just north of Leo Minor, faint-third-magnitude (3.45) Tania Bor is a class A2 subgiant that lies 134 light years away, 70 percent farther than the middle five Dipper stars that make the most notable portion of the Ursa Major Cluster. With a surface temperature of 8930 Kelvin, it radiates at a rate 59 times greater than does the Sun, which leads to a radius of 3.2 times solar, and from the theory of stellar structure and evolution, a mass of 2.5 times solar. Though nearing the end of its core hydrogen fusing lifetime, it seems not to be a subgiant (a star that has just given up such fusion), but an older dwarf with an age of 480 million years. Give it another 100 million and the formal class will finally apply. As do many stars of its kind, it appears to have an infrared enhancement (though quite mild) caused by some sort of dusty circumstellar debris. More significantly, Tania Bor is a "mild metallic line star" that (relative to hydrogen and compared to the Sun) is enriched in zinc and the rare earths (europium for example up from solar by a factor of 100) and deficient in calcium. The variations from solar are caused by gravity acting one way on some atoms, radiation acting the other, in a relatively quite atmosphere. And sure enough, compared with some, Tania Bor has a modest projected equatorial rotation speed of 50 kilometers per second, giving it a rotation period of under 3.2 days. The metallic differences are not enough, however, to give it an "Am" class like more extreme Xi Cephei or Mu Ori A. (Thanks to Jerry Diekmann, who suggested this star.)
Written by Jim Kaler 1/04/08. Return to STARS.