Lithium Depletion in Pre-Mainsequence Solar-Like Stars

Abstract

We examine the internal structure of solar-like stars in detail between 0.8 and 1.4M Sun and during pre-main sequence phase. Recent opacity computations of OPAL along with a new hydrodynamical mixing process have been considered. We also introduce up-to-date nuclear reaction rates and explore the impact of accretion, mixing-length parameter, non-solar distributions among metals and realistic rotation history. We compare models predictions of lithium depletion to the $^7Li$ content observations of the Sun and to 4 young clusters of different metallicities and ages. We show that we can distinguish two phases in lithium depletion: 1- a rapid nuclear destruction in the T-Tauri phase before 20 Myrs : this is independent of the mass used within our range but largely dependent on the extension and temperature of the convective zone, 2- a second phase where the destruction is slow and moderate and which is largely dependent on the (magneto)hydrodynamic instability located at the base of the convective zone. In terms of composition, we show the interest on considering helium and especially the mixture of heavy elements : carbon, oxygen, silicium and iron. We outline the importance of O/Fe ratio. We note a reasonable agreement on lithium depletion for the two best known cases, the Sun and the Hyades cluster for solar-like stars. Other clusters suggest that processes which may partly inhibit the predicted premainsequence depletion cannot be excluded, in particular for stars below ~ 0.9M Sun. Finally we suggest different research areas such as initial stellar models and more realistic atmospheres which could contribute to a better understanding of this early phase of evolution and which should become the object of subsequent research.