Just as comprehensive stellar models are essential for calibrating the ISO instruments, so also are reliable calibrations essential for understanding the spectra of stars with dynamic atmospheres. Josef Hron and Bernhard Aringer showed us how difficult it is to account for the atmospheres of Asymptotic Giant Branch (AGB) stars, where theoretical models would require a detailed understanding of the properties of dust, stellar pulsations, winds, mass loss, and shocks. Here, well-calibrated spectra from ISO are in strong demand for more sophisticated atmospheric modeling.
Takashi Onaka showed us spectra and photometric observations of two oxygen-rich Mira variables obtained over an entire cycle of light variations. A great deal of work remains to be done before we fully understand these complex stars. Their mass loss rates remain uncertain by at least an order of magnitude, and these loss rates will need to be understood if we are to determine the relative extent to which variable stars, as contrasted to novae and supernovae, enrich the interstellar medium with heavy nuclear species. ISO's spectral resolution may not suffice to provide all the information that will ultimately be needed to fully model atmospheric dynamics, wind velocities at different distances from the star, the chemical species at these distances, the radial distances at which dust grains first nucleate, and the rates at which grains subsequently grow, but data obtained to date are already providing new insights.