  Spectroscopic observations at 2.4 - 45 microns of the young supernova remnant
Cas A with the Infrared Space Observatory (ISO) Short Wavelength Spectrometer
(SWS) reveal strong emission lines of O, Ne, Si, S, and Ar. These lines are
observed at high velocities (several thousand km/s), and are therefore
associated with the supernova ejecta known as the fast-moving knots (FMKs).
Continuum emission from dust is also seen in the Cas A spectrum. The continuum
strength is spatially well correlated with the O and Ar line strengths,
indicating that the dust emission also arises from the FMKs. The dust continuum
has an emission feature at ~22 microns which cannot be fit by typical
astronomical silicates, but can be fit with a particular class of silicate
minerals. This suggests that the dust in Cas A is silicate material that has
freshly condensed from the Cas A ejecta into a mineral form that is
uncharacteristic of typical ISM dust grains.
