On the Significance of Population II6Li Abundances

We explore possible depletion factors for Li6 in the three stars where it hasbeen detected. To this end, we assume that 6Li/H scales as 16O/H throughout thegalactic evolution, an assumption motivated by the observations of a similarscaling for 9Be. We examine the uncertainties attached to this modeling of 6Ligalactic evolution; we also incorporate a recent evaluation of the primordialproduction of 6Li. The depletion factor D6, for 6Li, in HD84937, is constrainedto be less than 4 at 95% c.l.. This depletion factor is an extreme upper limiton the depletion factor for 7Li. We conclude that the primordial abundance of7Li cannot be higher that twice the observed value, since no current stellarmodel is able to reproduce the observed trends of 7Li with temperature andmetallicity, and yet deplete 7Li by more than a factor 2, while satisfyingD6<4. All three 6Li observations are in excellent agreement with all standardexpectations: Big-Bang nucleosynthesis with 2<$\eta_{10}$<6.5, and standardisochrones of 6Li survival. We discuss possible deviations from our assumptionof 6Li/H scaling with 16O/H, due to alpha-alpha creation of 6Li in varioussites. We notably reject stellar flares as a significant source of 6Li inHD84937.Comment: 19 pages, 4 figures, LaTeX. To appear in Ap