Newly synthesized elements and pristine dust in the Cassiopeia A supernova remnant

Spectroscopic observations at 2.4-45 mu m of the young supernova remnant Cas A with the Infrared Space Observatory (ISO) Short Wavelength Spectrometer reveal strong emission lines of O, Ne, Si, S, and Ar. These lines are observed at high velocities (several 10(3) km s(-1)) and are therefore associated with the supernova ejects 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, which indicates that the dust emission also arises from the FMKs. The dust continuum has an emission feature at similar to 22 mu m which cannot be fitted by typical astronomical silicates but can be fitted 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.