Stellar Evolution toward Pre-Supernova Stage. I: Carbon and Oxygen Stars of 5M , 10M and 30M

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Abstract
The evolution of carbon-oxygen stars of 5M⊙, 10M⊙ and 30M⊙ is computed from a pre-carbon-burning contraction stage to a pre-supernova stage through the phases of central burning of C, Ne, O, Mg, Si and Ni. These stars are regarded as representing the cross inside the helium shell-source of ordinary evolved stars. The computation is made for the two alternative cases, with and without neutrino production by electron-neutrino interaction. It is found that in the case without neutrinos the stars contract nearly homologously with structure almost similar to the polytrope of index 3 and each central burning begins gently. Finally, the stars of 5M⊙ and 10M⊙ become unstable on account of the photo-disintegration of iron, while the star of 30M⊙ becomes unstable in a central neon-burning phase by electron pair production. In the case with neutrinos, energy loss through neutrinos accelerates the evolution and, at the same time, gives rise to a deviation from the homologous contraction. The stars tend to be centrally condensed with evolution and both O and Si begin to burn at the center as strong flashes. Finally, all of the stars become unstable after the formation of an iron core.

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