Comparison of Observed and Synthetic Spectra of AGB-Stars: A Progress Report

We have calculated a set of synthetic spectra for AGB-stars using the MARCS-code (Gustafsson et al., 1975) and improved spectral synthesis. Here we investigate the spectral changes as a function of the stellar parameters and we show a comparison of observed high resolution UVES spectra of galactic disk and bulge AGB-stars with calculated synthetic spectra. Using our set of synthetic spectra, we try to determine the stellar parameters using only these and (J - K) data (Schultheis 1998). To achieve this, we use a minimal-distance method and search for spectral features which can be used as indicators that are sensitive either only to a change in Teff or only to a change in metallicity [M/H] (where M are all metals from Li to U). In a later stage of the project, we will focus on selected lines of s-process elements in an attempt to achieve a more accurate abundance determination leading to a better understanding of nucleosynthesis and dredge-up processes in these stars.