Spectra of Cassiopeia A. II. Interpretation

The observations of Cas A presented in Paper I are discussed in the context of shock wave emission models computed by Raymond. The models for the brightest quasi-stationary flocculi indicate an overabundance of He and N relative to H by an order of magnitude. This implies that the gas was originally part of the H-burning core and that presupernova mass loss penetrated this region. The abundances of the fast-moving material support the hypothesis that this is uncontaminated material from the core of a massive star. Relative to O, we have abundance estimates for S, Ar, Ca, Fe, and Ne and have upper limits for H, He, N, Mg, and C. These results are compared to the stellar evolution calculations of Arnett and Schramm, and there is an indication that the presupernova star was very massive. Future searches for lines of He, Mg, and C will be of interest because they are predicted to be near the present detection limit