E. Tognelli, S. Degl'Innocenti, P. G. Prada Moroni
The disagreement between theoretical predictions and observations for surface lithium abundance in stars is a long-standing problem which indicates that the adopted physical treatment is still lacking in some points. However, thanks to the recent improvements both in models and observations, it is interesting to analyse the situation to evaluate present uncertainties. We thus present a consistent and quantitative analysis of the theoretical uncertainties affecting the current generation of models. Theoretical predictions have been tested against observational data for five open clusters, namely Ic 2602, \alpha Per, Blanco1, Pleiades, and Ngc 2516, and four detached double-lined eclipsing binary systems. We restrict our analysis to young clusters, to avoid additional uncertainty sources such as diffusion and/or radiative levitation efficiency. By means of an up-to-date and well tested evolutionary code, i.e. FRANEC, theoretical uncertainties on surface lithium abundance predictions, during the pre-main sequence (pre-MS) and main sequence (MS) phase, are discussed in detail. Stellar models for the aforementioned clusters are computed by adopting suitable chemical composition, age and mixing length parameter for MS stars determined from the analysis of color-magnitude diagram of each cluster. Then, the surface lithium abundances obtained from these computations are compared with the data made available by a recent and homogeneous lithium-7 database. We confirm the disagreement, within present uncertainties, between theoretical predictions and lithium-7 observations for standard models. However, we notice that a satisfactory agreement with observations for lithium-7 abundance in both young open clusters and binary systems can be achieved if a lower convection efficiency is adopted during the pre-MS phase with respect to the MS one.
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http://arxiv.org/abs/1210.4134
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