Lithium and Lithium Depletion in Halo Stars on Extreme Orbits

We have determined Li abundances in 55 metal-poor (3.6 < [Fe/H] < -0.7) starswith extreme orbital kinematics. We find the Li abundance in the Li-plateaustars and examine its decrease in low-temperature, low-mass stars. The Liobservations are primarily from the Keck I telescope with HIRES (spectralresolution of ~48,000 and median signal-to-noise per pixel of 140). Abundancesor upper limits were determined for Li for all the stars with typical errors of0.06 dex. Our 14 stars on the Li plateau give A(Li) = log N(Li)/N(H) + 12.00 of2.215 +-0.110, consistent with earlier results. We find a dependence of the Liabundance on metallicity as measured by [Fe/H] and the Fe-peak elements [Cr/H]and [Ni/H], with a slope of ~0.18. We also find dependences of A(Li) with thealpha elements, Mg, Ca, and Ti. For the n-capture element, Ba, the relationbetween A(Li) and [Ba/H] has a shallower slope of 0.13; over a range of 2.6 dexin [Ba/H], the Li abundance spans only a factor of two. We examined thepossible trends of A(Li) with the characteristics of the orbits of our halostars, but find no relationship with kinematic or dynamic properties. The starscooler than the Li plateau are separated into three metallicity subsets. Thedecrease in A(Li) sets in at hotter temperatures at high metallicities than atlow metallicities; this is in the opposite sense of the predictions for Lidepletion from standard and non-standard models.Comment: 29 pages including 3 tables and 12 figures Accepted by The Astrophysical Journal, for the 1 November 2005 issue, v. 63