New Astronomy, 4, 255-263 (1999/July-0)
The evolution of ^6Li in standard cosmic-ray nucleosynthesis.
FIELDS B.D. and OLIVE K.A.
Abstract (from CDS):
We review the Galactic chemical evolution of ^6Li 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 alpha off of CNO nuclei in the ambient interstellar medium. If O/Fe is constant at low metallicities, then the ^6Li versus Fe/H evolution - as well as Be and B versus 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 ^6Li evolution in a standard model of cosmic-ray nucleosynthesis is consistent with the data. We also show that another key indicator of ^6LiBeB origin is the ^6Li/Be ratio which also fits the available data if O/Fe is not constant at low metallicity. Finally we note that ^6Li evolution in this scenario can strongly constrain the degree to which ^6Li and ^7Li are depleted in halo stars.