New light on the old problem of lithium pre-main sequence depletion: models with 2D radiative-hydrodynamical convection

Abstract

The T eff location of pre-main sequence (PMS) evolutionary tracks depends on the treatment of overadiabaticity. We present here the PMS evolutionary tracks computed by using the mixing length theory (MLT) of convection in which the α MLT = l/H p parameter calibration is based on 2D hydrodynamical models by Ludwig et al. These MLT-α 2D stellar models and tracks are very similar to those computed with non-grey ATLAS9 atmospheric boundary conditions and full spectrum of turbulence (FST) convection model both in the atmosphere and in the interior. The comparison of the new tracks with the location on the Hertzsprung-Russell (HR) diagram of PMS binaries is not completely satisfactory, as some binary components are located at too low T eff . Besides, the PMS lithium depletion in the MLT-α 2D tracks is still much larger than that expected from the observations of lithium in young open clusters. This result is similar to that of FST models. Thus, in spite of the fact that 2D radiative-hydrodynamical models should provide a better convection description than any local model, their introduction is not sufficient to reconcile theory and observations. Lithium depletion in young clusters points towards a convection efficiency which, in PMS, should be smaller than in the MS. The PMS lithium depletion decreases significantly in FST models if we reduce the solar metallicity down to the value suggested by Asplund et al., but the corresponding solar model does not reproduce the depth of the convective zone as determined by helioseismology.