Pre-Main-Sequence Stages of Stars

Evolutionary model sequences of gravitationally contracting stars were calculated for masses, 0.4, 0.6, 1.0, 1.5, 2.0 and 3.0M , by using the surface condition based on the conventional mixing length theory of convection and assuming the contraction to be homologous. The mixing length was assumed to be equal to 1-pressure scale height. The interpolation formula of opacity based on the table of KELLER and MEYERoTT was used for the radiative core. Evolutionary tracks are shown in the H-R diagram and loci of constant age are compared with the observational data. General features of models and evolutionary tracks are in agreement with those' of C. HAYASHI et al. For some models, mean life times of lithium were calculated and the results show that even Li6 can little be depleted during the pre-mainsequence stage of a star of one solar mass if the mixing length equals 1-pressure scale height.