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L.J. Hainline, C.P. Deliyannis (Indiana U.)
Halo dwarfs exhibit a plateau of lithium abundances near 12 + log [ N(Li)/N(H) ] = A(Li) = 2.1-2.3, whereas young open cluster stars that are minimally depleted in lithium and the meteoritic abundance are A(Li) = 3.2-3.4. Although the amount of depletion of the halo star Li abundances is still vigorously debated, it is generally agreed that their initial abundances were not as high as A(Li) = 3.2-3.4; therefore, lithium production processes in the Galaxy raised the ambient Li abundance from its Big Bang value (whatever that may be) to about A(Li) = 3.2-3.4. In a plot of [Fe/H] vs. Li, one sees a rather flat plateau of Li abundances from the lowest metallicities near [Fe/H] = -3.5, all the way up to [Fe/H] = -0.3 or so, then a very steep rise to A(Li) = 3.2-3.4 at solar metallicity. Attempts to explain this steep rise in Li have invoked models using lithium production from a) cosmic rays, b) supernovae (neutrino process), c) novae, and d) the 7Be-transport mechanism in AGB stars, in various combinations, and have met various degrees of success; a possible slight rise in the Li abundances with [Fe/H] at [Fe/H] < -1, if real, is adequately matched by models of cosmic ray Li production. However, regardless of whether comsic ray models are trying to explain a completely flat halo Li plateau, or are trying to reproduce a possible slight rise, these models invariably produce a factor of 2-4 more Li at intermediate metallicities ([Fe/H] -1 to -0.3) than is observed. To help ascertain whether this is a deficiency in the models, or an artifact of the small number of observations available at intermediate metallicity, we present observations of Li in 118 stars with [Fe/H] mostly in the range -0.6 to -0.4, taken at the WIYN 3.5m telescope at KPNO, with high signal-to-noise (about 200) and high resolution (about 15,000). This work is supported by NSF Grant AST-9812735.