Lithium Abundances of the Most Metal Poor Stars

Abstract

Recent studies of halo main-sequence turnoff stars with [Fe/H] < −3.0 have yielded some lower Li abundances than are normally associated with Population II dwarfs, by 0.10 to 0.15 dex. Two possibilities are considered: (i) that the most metal poor stars have depleted their surface Li relative to higher metallicity halo dwarfs, or (ii) that some non-primordial production of Li is evident in halo dwarfs. It may be difficult to reconcile (ii) with galactic chemical evolution models, and there is no prediction in stellar evolution calculations that (i) would occur; the correct explanation for the observations remains unclear. It is unclear whether studying the most metal poor stars leads one closer towards or further away from the primordial Li abundance. Current NLTE calculations for the Li resonance doublet do not significantly affect the arguments.