The Evolution of Li in Standard Cosmic-Ray Nucleosynthesis

We review the Galactic chemical evolution of Li and compare these results with recent observational determinations of the lithium isotopic ratio. In particular, we concentrate on so-called standard Galactic cosmic-ray nucleosynthesis in which Li, Be, and B are produced (predominantly) by the inelastic scattering of accelerated protons and α’s off of CNO nuclei in the ambient interstellar medium. If O/Fe is constant at low metallicities, then the Li vs Fe/H evolution–as well as Be and B vs Fe/H–has difficulty in matching the observations. However, recent determinations of Population II oxygen abundances, as measured via OH lines, indicate that O/Fe increases at lower metallicity; if this trend is confirmed, then the Li evolution in a standard model of cosmic-ray nucleosynthesis is consistent with the data. We also show that another key indicator of LiBeB origin is the Li/Be ratio which also fits the available data if O/Fe is not constant at low metallicity. Finally we note that Li evolution in this scenario can strongly constrain the degree to which Li and Li are depleted in halo stars. Subject headings: cosmic-rays – Galaxy :abundances – nuclear reactions, nucleosynthesis, abundances