Propagation of shock waves in type-II presupernovae

We explore the reliability of the approximate methods which are used to est imate the velocity and temperature at the front of a shock wave that passes in a type-II presupernova successively through the carbon-oxygen shell, th e helium shell, and the base of the hydrogen-helium envelope. This issue de serves a special consideration, because the attendant nucleosynthesis depen ds on the shock-front temperature and on other hydrodynamic parameters. The temperature of the shock-heated matter in the carbon-oxygen and silicon sh ells is shown to be so high that the contribution of electron-positron pair s to the equation of state becomes appreciable.