Nucleosynthetic Layers in the Shocked Ejecta of Cassiopeia A. (arXiv:1208.4034v1 [astro-ph.SR])

Nucleosynthetic Layers in the Shocked Ejecta of Cassiopeia A. (arXiv:1208.4034v1 [astro-ph.SR]):
We present a 3-dimensional analysis of the supernova remnant Cassiopeia A
using high resolution spectra from the Spitzer Space Telescope. We observe
supernova ejecta both immediately before and during the shock-ejecta
interaction. We determine that the reverse shock of the remnant is spherical to
within 7%, although the center of this sphere is offset from the geometric
center of the remnant by 810 km/s. We determine that the velocity width of the
nucleosynthetic layers is approximately 1000 km/s over 4000 square arcsecond
regions, although the velocity width of a layer along any individual line of
sight is <250 km/s. Si and O, which come from different nucleosynthetic layers
in the progenitor star, are observed to be coincident in velocity space in some
directions, but segregated by up to approximately 500 km/s in other directions.
We compare these observations of the nucleosynthetic layers to predictions from
supernova explosion models in an attempt to constrain such models. Finally, we
observe small-scale, corrugated velocity structures that are likely caused
during the supernova explosion itself, rather than hundreds of years later by
dynamical instabilities at the remnant's reverse shock.