Metallicity calibration of theoretical stellar SEDs using UBVRIJHKL photometry of globular clusters

Abstract

Although stellar SED models are constantly improving and seem to show similar differential tendencies as measured spectra, their absolute properties (eg. absolute flux in different wavelength regions) can still differ significantly from the measured ones. Therefore, it is necessary to "color-calibrate" the theoretical spectra to obtain realistic model-based stellar spectra, which can then be used for many purposes, such as population synthesis models. In order to calibrate a hybrid library (consisting of the Kurucz -, the Allard and Hauschild -, and the Scholz-models) of theoretical SEDs, UBVRIJHKLM photometric data of solar neighborhood stars were collected from the literature, and the solar metallicity models were calibrated using an algorithm developed by Cuisinier et. al. The corrections were then propagated through the whole grid of models, resulting in the "semi-empirical" models (available on ftp from the university of Basel). In order to extend the calibration to non-solar abundances, we have collected UBVRIJHKL photometric data from well-known Galactic globular clusters, covering a wide range of metallicities. We shall present first results, using the metallicity-calibrated library for calculating isochrones of metal-poor clusters. In particular, the observed slope and/or curvature of the RGB appears to be reproducible in a systematically correct manner for the first time.