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==> In this proposal, more time is being requested for RWATERS.POSTAGB
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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).