Roger A. Chevalier

Abstract: If we assume that type II supernovae result from the explosion of evolved massive stars, the structure of the presupernova star is expected to be as follows. At the center is a very dense core region of mass 1.4 90îo; its collapse gives rise to the supernova energy. Outside of this is a dense mantle of processed elements, and, finally, an extended envelope of radius —TO cm. Much of the envelope mass is at near constant density. Supernova models have been computed in which an energy of 10 ergs is deposited in the center of a mantle-envelope structure. This energy was chosen to give final velocities compatible with observations. After the deposition of energy, the mantle formed a dense shell which was decelerated by the envelope. The supernova energy was transferred to the envelope and a reverse shock wave drove the mantle material back toward the center while the envelope was expanding at high velocity. The envelope formed a shell which dominated the observable characteristics of the supernova around maximum light. The observed photometric properites of a supernova near maximum light (photospheric temperature — 10,000° K and radius —10 cm) were reproduced. The models showed that the gas velocity at the photosphere is a sensitive indicator of the outer density structure of the presupernova. The sharp de-