Pre-main sequence evolutionary tracks and lithium burning

Abstract

A review about the main physical uncertainties still weighing upon the computation of Pre Main Sequence (PMS) evolutionary tracks is given, in order to evaluate (at least qualitatively) their possible influences upon the surface stellar parameters. It is shown that we are not yet able to reliably compare observations with theoretical luminosities and colours, and also the correlation between initial stellar parameters (mass and chemical composition) and expected lithium depletion in PMS is not very sound. In particular, even if updated evolutionary models seem to show that Li-depletion in the Sun during PMS can be marginally consistent with the observations, several problems still remain unsolved. In this framework, the observed spread of Li-abundances among Main Sequence (MS) stars belonging to a given young cluster, is attributed to the influence of rotation and magnetic fields (and perhaps accretion), which largely affect Li-depletion. The spread observed among different young clusters is instead likely to be due to intrinsic differences, mainly in the chemical compositions.