Institut fur Astronomie, ETH-Zentrum, CH-8092 Zurich, Switzerland
We obtained well exposed SWS and LWS spectra from the symbiotic red giant CH Cyg. This object is interesting because it is a nearby, very late and bright M giant. It is also part of a symbiotic binary system but the symbiotic activity is presently declining. Correspondingly an increased dust production is expected to take place.
We fitted dust models to the data and find good agreement for a silicate dust shell condensing at about 5 stellar radii and extending out to a few hundred stellar radii. The emission at short wavelengths up to 6 mum is dominated by photospheric emission and comparison with model atmospheres yields a stellar angular diameter which, with the HIPPARCOS parallax, yields a stellar radius of 280 solar radii.
The SWS spectrum shows a large number of molecular absorption lines of OH and CO and of (up to now) unidentified species. Some of the molecular features are seen in the continuum produced by dust and therefore are probably circumstellar in origin.