The 9Be Abundances of alpha Centauri A and B and the Sun: Implications for Stellar Evolution and MixingThe Astrophysical Journal
PublisherThe American Astronomical Society
AbstractWe present high-resolution, high signal-to-noise ratio spectra, obtained at the Cerro Tololo Inter-American Observatory 4 m telescope, of the Be II 3131 Å region in the metal-rich solar analog α Centauri A and its companion α Centauri B. Be abundances are derived relative to the Sun in a consistent fashion via spectrum synthesis. For α Cen A, we find [Be/H] = +0.20 ± 0.15, where the error reflects random uncertainties at the 1 σ confidence level; systematic errors of ~0.1 dex are also possible. The analysis of α Cen B is more uncertain since inadequacies in the line list, which was calibrated with solar data, may manifest themselves in cool metal-rich dwarfs. Our analysis suggests [Be/H] +0.05, which is lower than the value of A, but not significantly so given the uncertainties in the A determination alone. In order to derive a conservatively probable and larger extreme range for the solar photospheric Be abundance, we consider various uncertainties (including those in the gf-values, continuum location, non-LTE effects, model atmospheres, analysis codes, and contaminating blends) in its determination. We conclude that the probable range of depletion of photospheric Be from the meteoritic value is 0.16-0.50 dex. Our larger extreme range is 0.05-0.62 dex. Even a slight real depletion in solar photospheric Be itself would strongly contradict the standard solar model (as does the Sun's Li depletion), suggesting the action of additional mechanisms. When coupled with the solar Li depletion of only ~2 dex, Be depletion would point to mixing mechanisms (possibly rotationally induced) below the surface convection zone acting on a timescale that is much longer than the convective timescale. If the difference in the Be abundances of α Cen A and B is real, it too would strongly suggest the action of additional mixing mechanisms. The study of both stars with higher resolution data and improved atomic and molecular data is clearly important. We conclude that the light-element abundances of the Sun and α Cen A (and other solar analogs) are not grossly dissimilar. 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 also have considered the issue of the unidentified blending feature(s) in the Be II 3131.065 Å region. While a putative Mn I λ3131.037 feature has several favorable characteristics, we suggest that a single significant blending feature likely lies ~0.02 Å blueward of this position.
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