Mixing of Ejected Material in Supernova Remnant Cas A

Cas A is the well known supernova remnant and detailed observational data have been accumulated. In particular, recent observations suggest that the element distributions for silicon (Si) and iron (Fe) are very peculiar: Fe locates in front of Si. On the other hand, the distribution has not been well studied in connection with supernova remnants. Therefore, we investigate the formation of the remnant of Cas A. Hydrodynamical calculations are performed from the beginning of explosion to the present stage. Before the explosion, models of circumstellar matter are constructed, where the matter is assumed to be ejected from a progenitor. As the supernova simulation of explosion, two dimensional hydrodynamical calculations are performed. It is found that the Rayleigh-Taylor instability is developed from the boundary between hydrogen and helium layers.The instability between Si and Fe layers is not grown enough to induce the observed matter mixing if only the mass loss is included during the red super giant stage. We suggest that an instability at the boundary between Si and Fe layers ascribed to the mass loss during the Wolf-Rayet stage could explain the observations