PMS evolution of standard non-accreting models with masses M = 0.7 and 0.8 M_⊙, and Z = 0.0001. Left panel: evolution in the HR diagram. We marked the position of the models at 1 Myr (filled triangles) and 10 Myr (filled squares). Right panel: evolution of the temperature at the base of the convective envelope as a function of age. The yellow shaded zone shows the Li-burning temperature range (T_Li = 2.5−3.2 × 10⁶ K, see text). We also marked the region where the deuterium burning supplies more than 50% of the total luminosity (thick magenta line).