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[43.12] Nucleosynthesis and Mixing in Cassiopeia A

C.E. Rakowski, J.P. Hughes (Rutgers, The State University of New Jersey), D.N. Burrows (Penn State University), P.O. Slane (CfA)

The power of the spatial and spectral resolution of the Chandra X-ray Observatory is evident in the first light observations of the Cassiopeia A (Cas A) supernova remnant (SNR). There are spectral variations with position in Cas A on all spatial scales down to the resolution limit of the detector, roughly 0.02 pc at the SNR. Here we present studies of the X-ray spectra from a few, arcsecond-scale regions, comparing them to nonequilibrium ionization plasma emission models using the abundances expected from different nucleosynthesis processes. We present the first clear identification of Fe-rich regions with abundances indicative of explosive Si-burning, as well as Si-rich knots produced by explosive O-burning. Remarkably, we find that the Fe-rich knots lie outside the Si-rich knots, which points to a massive overturning of the nucleosynthesis products, given that the Si-burning occurs deeper in the progenitor star than O-burning does. In light of this finding, we re-examine the angular expansion of the X-ray remnant, focusing on the motion of these knots by comparing the Chandra data to earlier ROSAT and Einstein observations. The spectral dimension of Chandra allows us to map the Chandra data directly onto the different spectral band passes of ROSAT and Einstein, thereby eliminating a major source of uncertainty in previous expansion studies.