⁷Li surface abundance in pre-main sequence stars

Testing theory against clusters and binary systems

¹ Physics Department “E. Fermi”University of Pisa, largo B. Pontecorvo 3, 56127 Pisa, Italy
e-mail: tognelli@df.unipi.it
² INFN, largo B. Pontecorvo 3, 56127 Pisa, Italy

Received: 24 February 2012
Accepted: 8 October 2012

Abstract

Context. 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 in both models and observations, it is interesting to analyse the situation to evaluate present uncertainties.

Aims. We present a consistent and quantitative analysis of the theoretical uncertainties affecting surface lithium abundance in the current generation of models.

Methods. By means of an up-to-date and well tested evolutionary code, FRANEC, theoretical errors on surface ⁷Li abundance predictions, during the pre-main sequence (pre-MS) and main sequence (MS) phases, are discussed in detail. Then, the predicted surface ⁷Li abundance was tested against observational data for five open clusters, namely Ic 2602, α Per, Blanco1, Pleiades, and NGC 2516, and for four detached double-lined eclipsing binary systems. Stellar models for the aforementioned clusters were computed by adopting suitable chemical composition, age, and mixing length parameter for MS stars determined from the analysis of the colour−magnitude diagram of each cluster. We restricted our analysis to young clusters, to avoid additional uncertainty sources such as diffusion and/or radiative levitation efficiency.

Results. We confirm the disagreement, within present uncertainties, between theoretical predictions and ⁷Li observations for standard models. However, we notice that a satisfactory agreement with observations for ⁷Li 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.