The following document lists the file abstract/RARENDT_CASA_SWS.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
Observations of the Cas A supernova remnant in the 16 - 49 micron range with the KAO have revealed a stong continuum with a broad emission feature at 22 microns and a strong line at 26 microns (Moseley et al. in preparation). However, the KAO data lack the sensitivity and spectral resolution to clearly identify the nature of these features. The 26 micron line could potentially be either [O IV] or [Fe II]. The broad feature in the continuum spectrum is displaced to slightly longer wavelengths than the 20 micron feature found in most common silicate minerals. The position and shape of this emission feature are clearly unlike those previously observed in any astronomical source. The SWS observations we propose will have enough sensitivity and spectral resolution to allow more precise fitting of the continuum, and determination of the emissivity and nature of dust in Cas A. This unusual dust feature could either reflect the change in the optical properties of regular astrophysical silicates as they are exposed to the harsh post shock environment, or it could reflect the optical properties of pristine dust that has formed in the supernova ejecta. The wavelengths of the oxygen and iron lines are close enough and the range of velocities in the Cas A ejecta is high enough that spectral resolution alone will not allow unambiguous identification of the 26 micron line. The full spectral coverage of the SWS data should reveal the presence of another iron line at 35.4 microns, or other lines that were only hinted at in the KAO data ([S III] 18.7 microns, [Si II] 34.8 microns, and [Ne III] 36.0 microns). If the 26 micron line is iron it samples some of the heaviest ejecta (previously unseen) of the Cas A supernova. If the line is oxygen, then we have a new tracer of oxygen sampling hotter material than that observed at visual wavelengths and unobservable in the UV (where other O IV lines are found) due to the high extinction towards Cas A.