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TANIA BOREALIS (Lambda Ursae Majoris). Three pairs of unrelatedstars mark the feet ofUrsa Major, theGreat 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 thestars that make the "Second Leap," the name from a long phrase thatmeans just that (plus the Latin for "northern"). The southern starof the pair isTania Australis (MuUMa), while the first leap is made by Alula Borealis andAustralis (Nu and Xi), the third fromTalitha (Iota) andKappa UMa. Positioned just north ofLeo Minor, faint-third-magnitude (3.45) TaniaBor is a class A2 subgiant that lies 134 light years away, 70percent farther than the middle fiveDipper stars that make the most notable portion of theUrsa Major Cluster. With a surfacetemperature of 8930 Kelvin, it radiates at a rate 59 times greaterthan does theSun, which leads to a radiusof 3.2 times solar, and from the theory of stellar structure andevolution, a mass of 2.5 times solar. Though nearing the end ofits core hydrogen fusing lifetime, it seems not to be a subgiant (astar that has just given up such fusion), but an older dwarf withan age of 480 million years. Give it another 100 million and theformal class will finally apply. As do many stars of its kind, itappears to have an infrared enhancement (though quite mild) causedby some sort of dusty circumstellar debris. More significantly,Tania Bor is a "mild metallic line star" that (relative to hydrogenand compared to the Sun) is enriched in zinc and the rare earths(europium for example up from solar by a factor of 100) anddeficient in calcium. The variations from solar are caused bygravity acting one way on some atoms, radiation acting the other,in a relatively quite atmosphere. And sure enough, compared withsome, Tania Bor has a modest projected equatorial rotation speed of50 kilometers per second, giving it a rotation period of under 3.2days. The metallic differences are not enough, however, to give itan "Am" class like more extremeXi CepheiorMu Ori A. (Thanks to Jerry Diekmann,who suggested this star.) Written byJim Kaler 1/04/08. Return toSTARS.
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