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Session 58 - Stellar Modelling/Abundances.
Display session, Wednesday, June 12
We present high resolution high S/N spectra, obtained at the CTIO 4-m, of the Be II 3131 Åregion in the metal-rich solar analog \alpha Cen A and its companion \alpha Cen B. Be abundances are derived relative to the Sun in a consistent fashion via spectrum synthesis. For \alpha Cen A, we find [Be/H]=+0.20\pm0.15 where the error reflects random uncertainties at the 1\sigma confidence level; systematic errors of \sim0.1 dex are also possible. Analysis of \alpha Cen B is more uncertain since inadequacies in the linelist, which was calibrated with Solar data, may manifest themselves in cool metal-rich dwarfs. Our analysis suggests [Be/H]\la+0.05. We also consider numerous uncertainties in the Solar photospheric and meteoritic Be abundances and conclude that it is likely the former value is depleted relative to the latter by 0.1-0.5 dex. Even a slight real depletion in solar photospheric Be coupled with the observed Li depletion of only \sim2 dex would favor a slow (possibly rotationally-induced) mixing mechanism in addition to standard model burning at the base of the convection zone. If the difference in the Be abundances of \alpha Cen A and B is real, it too would strongly suggest the action of additional mixing mechanisms. The light element abundances of the Sun and \alpha Cen A (and other Solar analogs) are not grossly dissimilar. Thus, the idea that standard models and the current solar photospheric Li and Be abundance are discrepant because the Sun is a lone ``oddball'' is doubtful. We consider the issue of the unidentified blending feature(s) in the 3131.065 ÅBe II region: a single significant blending feature could possibly fit the solar spectrum if it lies near \lambda3131.02.
Program listing for Wednesday