PRIMORDIAL LITHIUM - KECK OBSERVATIONS IN M92 TURNOFF STARS

We present new Keck I/HIRES observations at R = 45,000 (=3 pixels) of seven stars near the turnoff of the old, metal-poor globular cluster M 92. In three of these stars, we have signal-to-noise ratios (S/Ns) of 40 pixel(-1), and in the other four, the S/N is near 20. The Li abunda nce in star 18 is high compared with the halo held-star plateau and is similar to that in the remarkable Li-rich halo field star ED +23 degr ees 3912. In addition to the high Li abundance in star 18, there is a dispersion in Li abundance in our seven stars covering the full range of a factor of 3. We have attempted to determine whether the excess Li in star 18 is due to less than average Li depletion in this star from an even higher initial abundance, as predicted by the Yale rotational models, or whether it is due to the extraordinary action of Li produc tion mechanisms in the material that formed this star. We have found n o convincing evidence that favors Li production: (1) Stars 18, 21, and 46 have identical Ba abundances, which argues against Li production c arrying an s-process signature. (2) These three stars have indistingui shable Ca, Cr, Fe, and Ti, which argues against supernova Li productio n. (3) We discuss v-process production of Li and find no convincing ob servational evidence for this from the strengths of the Mg, Ca, and Fe lines. (4) The similarity in age of these cluster stars argues agains t cosmic-ray Li production that requires age differences of gigayears. The most likely explanation for the Li dispersion is differential Li depletion from a (possibly significantly) higher primordial Li abundan ce due to differences in the initial angular momentum in each star fol lowed by spin-down; the most rapid rotators destroy the most Li, where as the initially slower rotators preserve more Li.