Evolu.tion of Carbon StarsQ II --Carbon Burning Phase--

The stage of the zero-age carbon main-sequence and the subsequent evolution due to the depletion of carbon are studied for carbon-oxygen stars, which are regarded as representing the carbon-oxygen cores of ordinary stars having hydrogen and helium envelopes. The structure in the zero-age stage is computed for several stellar masses between a minimum value and 401\118 , and the evolution is computed for the masses, 1.0, 2.6 and 1O.OMCO). These computations are made for the two alternative cases, with and without neutrino loss. It is found that the neutrino loss reduces the lifetime of the carbon-burning phase at least by a factor of 30. By reference to the preceding study of the gravitational contraction phase, the lifecime of an ordinary star of 15.62\10 as a red supergiant is obtained. The time of evolution without neutrino loss is consistent with the observed numbers of red supergiants in the star clusters, h+x Persei and NGC 330, but the evolution with neutrinos is faster by a factor of 20. Finally, discussions are made of the effects of rotation, helium flicker and mass loss on the lifetime. It seems unlikely that these effects are large enough to increase the lifetime by a factor as large as 20.