Newly Synthesized Elements and Pristine Dust in the Cassiopeia A Supernova Remnant

Abstract

Spectroscopic observations at 2.4È45 km 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 103 km s~1) 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, which indicates that the dust emission also arises from the FMKs. The dust continuum has an emission feature at D22 km which cannot be Ðtted by typical astronomical silicates but can be Ðtted 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. Subject headings : dust, extinction È infrared : ISM : continuum È infrared : ISM : lines and bands È ISM : individual (Cassiopeia A) È supernova remnants