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==> In this proposal, more time is being requested for FKERSCHB.ORICHSRV
==> Time for this proposal is to be transferred from FKERSCHB.ORICHSRV
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Systematic studies of the basic properties of type SRa and SRb Semiregular
variables (SRVs) have found that SRbs consist of a "blue" group without
circumstellar shells, short periods and higher temperatures and a "red" group
with temperatures and mass loss rates comparable to Miras but periods a factor
of 2 smaller. Near IR photometry shows that the "blue" SRVs are similar to
non-variable giants, while the "red" SRVs are intermediate objects between
Miras and normal giants. A subgroup of the Irregular variables of type Lb seem
to be very similar to the "red" SRVs except for their lightcurves.
The difference in atmospheric structure, most prominently seen in the strength
of the water bands, could be due to smaller pulsation amplitudes and weaker
shockfronts of the SRVs and Lbs. Thus, when compared to Miras and non-variable
giants, the "red" SRVs and Lbs can provide important clues for the influence of
the pulsational behaviour on the atmospheric structure and mass loss of AGB
stars. Many of the theoretical tools for interpreting the spectra of these
stars are available now. Since no detailed spectroscopic studies in the IR
exist, we propose SWS spectra of selected objects. These will be compared with
state of the art theoretical models. The SWS on board of ISO covers most of the
molecular bands of H2O, CO and SiO and the wavelength region where continuous
dust emission starts to dominate. While some of the mentioned bands can be
observed from the ground, this requires different instruments and often
excellent observing conditions. The use of different instruments generally
means that different molecular bands and the dust emission cannot be studied
at the same time, a severe disadvantage in view of the variability of AGB stars
and the pronounced coupling  between dust and different molecules.