We have presented digital spectra covering the spectral range from 0.5 to
2.5 m for a large sample luminous cool stars. The amazing variety
of spectral properties found in the sample and the strong variations seen with
phase in variable stars illustrate the sensitivity of many
molecular features to the detailed structure of the atmosphere.
Features such as the water vapour bands are particularly strong
in variable stars, as compared to (quasi-)static giants, because
of the atmospheric extension pulsation leads to. Frequent cycle-to-cycle
variations make it compulsory to obtain complete data sets simultaneously,
as it was done here, if the data are to be compared with model
predictions or used for classification.
Although correlations exist between spectral properties and dynamical properties such as period and amplitude, they show a large dispersion. A more complete phase coverage of the pulsation cycle and, simply, a better phase and instantaneous luminosity information for the available data would help clarifying these relationships. The work of amateur astronomers in organisations such as the AAVSO and AFOEV will hopefully continue to provide such invaluable information.
The spectra of this paper may be used for population synthesis purposes. Methods, predictions and the necessary empirical calibration of the model predictions are discussed elsewhere (Lançon et al. 1999; Mouhcine & Lançon 2000; Mouhcine et al., in preparation).
Acknowledgements
This work made extensive use of the Simbad and Vizier literature search tools, operated at CDS, Strasbourg. We sincerely thank P. McGregor for invaluable help with IR observations in general and the analysis of CASPIR data in particular; we have also greatly appreciated the help of the MSSSO observer support team and computing section. A.L. thanks L. d'Hendécourt for helpful discussions on candidate chemical species for the 1.53m feature in RLep.
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