The following document lists the file abstract/RWATERS_CRYSTAL.abs
from catalogue VI/111.
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===================================================================== ==> In this proposal, more time is being requested for RWATERS.POSTAGB ===================================================================== ISO-SWS spectra of cool oxygen-rich dust shells reveal a wealth of solid state features which were previously not known. These features are narrow and are probably caused by new components in the circumstellar dust of evolved, oxygen-rich objects. We have identified crystalline silicates (Pyroxenes, Olivine) as one of the components. Several emission features are not yet identified. The spectra taken so far suggest that the new features occur in dust shells with colour temperatures less than about 300 K, i.e. in very red AGB stars, and in the detached envelopes of some post-AGB stars and planetary nebulae. The strength and shape of the features show large variations between objects. We propose to systematically investigate the new dust features with SWS (and LWS) by taking full scans at high S/N and high spectral resolution of a range of oxygen-rich objects with colour temperatures less than 500 K. This data set will allow us to make a comprehensive inventory of the spectral features, which is essential for a proper identification. Current observing programmes with ISO do not systematically obtain such high quality data for oxygen-rich sources. The new spectra will enable us to study the correlation between these features and properties such as mass loss rate, wind expansion velocity, the shape of amorphous dust features etc.. The new data will shed light on the dust formation processes in evolved stars with very high mass loss rates (the superwind). This is a very large observing programme, in which several groups are collaborating (see list of co-authors).