Die Lithiumhäufigkeit und die Struktur der äußeren Konvektionszone in sonnenähnlichen Sternen

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Abstract
The observations of the Lithium abundance and the isotope ratio Li6/Li7 in stars are briefly reviewed and some simple conclusions are drawn. It is emphasized that — in addition to the mechanism proposed by BODENHEIMER — a slow (timescale ≈ 109 years) mixing process in main sequence F and G stars is necessary to account for the observations. The present state of the theory of convective overshooting is reviewed in this context. Two new models of the outer solar convection zone are presented. The temperature at their lower boundaries are 2.04 x 106 °K and 2.27 x 106 °K, showing that only a rather small convective overshoot may be sufficient for mixing the matter in the convection zone with the layers, in which Li7 is burnt. Our models differ from earlier ones, because (when calculating the mean stratification) we take into account the condition that the mixing length can nowhere be larger than the distance from the nearest boundary of the convection zone. It is shown that this approach also leads to a slight change of the numerical factors in the formulae usually used.

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