Poster abstract details

The analysis of surface lithium abundance in open clusters is an indirect method to investigate the time evolution of the extension of the stellar convective envelope; in fact during the pre-main sequence and main sequence evolution of low and intermediate mass stars the temperature at the base of the convective zone is high enough to burn lithium. In this work we re-analysed the well known problem of the disagreement between theoretical predictions and data for the surface 7Li in clusters of different chemical composition and ages. In our procedure we rely on homogeneous data of observed 7Li abundances for cluster of different ages and chemical composition making also use of accurate observational colour-magnitude diagrams; the cluster age is directly derived by means of our theoretical isochrones. We show that it is possible to reproduce the 7Li depletion profile for young clusters (age below 100-200 Myr) adopting a value of the pre-main sequence mixing length parameter that is almost independent on both the mass and the chemical composition. Moreover we confirm that the depletion on a time scale larger than 200 Myr is incompatible with the hypothesis of standard mixing and diffusion, within the theoretical uncertainties