Kinematics of X-ray-emitting components in cassiopeia a

We present high-resolution X-ray proper-motion measurements of Cassiopeia A using Chandra X-Ray Observatory observations from 2000 and 2002. We separate the emission into four spectrally distinct classes: Si-dominated, Fe-dominated, low-energy-enhanced, and continuum-dominated. These classes also represent distinct spatial and kinematic components. The Si- and Fe-dominated classes are ejecta and have a mean expansion rate of 0.2% yr^-1. This is the same as for the forward shock filaments but less than the 0.3% yr^-1 characteristic of optical ejecta. The low-energy-enhanced spectral class possibly illuminates a clumpy circumstellar component and has a mean expansion rate of 0.05% yr^-1. The continuum-dominated emission likely represents the forward shock and consists of diffuse circumstellar material, which is seen as a circular ring around the periphery of the remnant as well as projected across the center.