Newly synthesized elements and pristine dust in the Cassiopeia A supernovaremnant

Spectroscopic observations at 2.4-45 mu m of the young supernova remnant Ca s A with the Infrared Space Observatory (ISO) Short Wavelength Spectrometer reveal strong emission lines of O, Ne, Si, S, and Ar. These lines are obse rved at high velocities (several 10(3) km s(-1)) and are therefore associat ed with the supernova ejects known as the fast-moving knots (FMKs). Continu um emission from dust is also seen in the Cas A spectrum. The continuum str ength is spatially well correlated with the O and Ar line strengths, which indicates that the dust emission also arises from the FMKs. The dust contin uum 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 o f silicate minerals. This suggests that the dust in Cas A is silicate mater ial that has freshly condensed from the Cas A ejecta into a mineral form th at is uncharacteristic of typical ISM dust grains.