Penet : ration of Convective Envelope into Stellar Core and Existence of Neutrino Loss

Evolution of Stars of masses 60Me, 20Me and 12Me is computed mainly for a limiting case where neutrino loss due to the universal Fermi interaction is completely neglected. Convective envelope penetrates deeply into the highly evolved core, but the depth of penetration is found to depend on the stellar mass and the efficiency of convective energy transport_ When the mixing proceeds quickly, the core mass is reduced finally below the Chandrasekhar limit and electrons become degenerate. When the mixing is relatively slow, on the other hand, decomposition of iron takes place in the core. When the degenerate core is formed, hydrogen is depleted uniformly in the envelope and the lifetime of this phase is much longer than one in the helium-burning phase. Moreover, in the bulk of that lifetime, the star remains to be a red supergiant, which is a peculiar star in its chemical composition. Thus both observed number ratio of blue to red supergiants and relative paucity of peculiar red supergiants support the existence of the neutrino loss, under the condition that the mixing length of convection is not appreciably smaller than unit scale height of pressure in the convective envelope. When the, neutrino loss is included, on the other hand, only a star as massive as 60Me may become a peculiar star as a result of the deep convective mixing, while the star of mass smaller than 30Me does not. Discussion concerning an origin of highly luminous peculiar stars .is also given.