To appear in The Astrophysical Journal, 1996
We model the Cassiopeia A supernova remnant in the framework of the circumstellar medium (CSM) interaction picture (Chevalier & Liang 1989). In this model, the slow red supergiant wind of the supernova (SN) progenitor was swept into a dense shell by a fast stellar wind in the subsequent blue supergiant stage of the progenitor star. The supernova blast wave propagated quickly (less than 100 years) through the tenuous wind-blown bubble located within this shell, and then slowed down in the dense (n_H approximately 15/cm3) CSM shell. The shell was impulsively accelerated during this interaction stage; during the subsequent interaction with SN ejecta, the shell has been further accelerated to approximately 2000 km/s, the currently observed expansion rate. The comparison of our X-ray emission calculations with the ASCA spectrum suggests that about 8 solar masses of X-ray emitting material is present in Cas A. Most of this mass is located in the CSM shell and in the outlying red supergiant wind. The X-ray continuum and the Fe K alpha line are dominated by the shell emission, but prominent K alpha complexes of Mg, Si and S must be produced by SN ejecta with strongly enhanced abundances of these elements. Our hydrodynamical models indicate that about two solar masses of ejecta have been shocked. An explosion of a stellar He core is consistent with these findings.
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