# Dusty wind envelopes

ISOPHOT Image at a wavelength of 90 microns of YCanum Venaticorum (This image was taken from the paper A detached dust shell surrounding the J-type carbon star Y Canum Venaticorum by Izumiura et al. 1996)

### Synthetic image (at 100 microns) computed from a two-component hydrodynamical simulation of a dusty AGB wind (Schoenberner, Steffen & Szczerba, 1998)

The expanding wind shells of very luminous and cool stars ("Red Giants") are cold and dense enough as to allow the formation of microscopic solid particles ("dust grains"), consisting mainly of silicates or carbon (soot). Due to their very large opacity, dust grains are efficient absorbers of radiative energy and momentum. Although only about 1% of the total mass is in the form of dust, it dominates the dynamics of the circumstellar shell once it has formed. For the highest mass loss rates, the central stars are completely obscured at visible wavelengths ("IR-stars"). Observationally, such objects are only detectable in the infrared due to emission originating from the cold circumstellar dust component. At radio wavelengths, the gas component radiates characteristic emission lines of different molecules (e.g. CO, OH). Modern infrared observations, in particular by the Infrared Space Observatory ISO, hold the key to clarify several hitherto unsolved problems and open questions of present day stellar astrophysics. A brief summary of the work on dusty AGB winds done by the "Stellar Physics" group at the AIP may be found in the documents Circumstellar Dust Shells and The puzzle of the circumstellar CO shells by M. Steffen & D. Schoenberner.

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