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==> In this proposal, more time is being requested for JHRON.VARLPV
==> This proposal requests an upgrade from Priority 3 for JHRON.VARLPV
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Variability is a characteristic feature of most AGB stars. Unfortunately,
spectroscopic time series covering many of the relevant molecular bands and
the dust emission simultaneously do not exist. Because of the different
sensitivity of various observable features to different parameters and
components of the atmosphere/envelope of an AGB variable (LPV) and because
of the strong and time dependent interplay of pulsation, dust and molecules,
such simultaneous and homogeneous data are the only way for a complete
understanding of the physical processes involved. From the theoretical side,
many of the tools for a quantitative interpretation of such complete
spectroscopic time series are available now. The SWS on board of ISO covers
the wavelength region where continuous dust emission starts to dominate and
most of the important features in the spectra of LPVs (molecular bands of CO,
SiO, H2O, CO2, HCN, C2H2 and C3, the solid state features of amorphous and
crystalline Silicates and SiC). While some of the mentioned bands and features
can be observed from the ground, this requires different instruments and
often excellent observing conditions. Other bands accesible with ISO are in
spectral regions where the Earth's atmosphere is completely opaque. Only ISO
can provide, probably for a long time, complete, homogeneous and simultaneous
data of the molecular features and the dust emission in the atmospheres and
envelopes of LPVs. Such data are a unique opportunity to test and improve
the time dependent models. For the proposal JHRON.VARLPV time series with SWS
have been started for four LPVs. However, in view of the many different
parameters influencing the time dependent models (C/O ratio, pulsational
properties, stellar temperature etc.) a larger set of stars is definitely
needed. We therefore propose to extend our ongoing ISO programme VARLPV.