5 Summary

In this work we present Monte-Carlo evolutionary synthesis models for SSPs which cover a wide range in metallicity, from Z=0.0001 to Z=0.05, using most recent and complete sets of input physics: stellar evolutionary tracks for stellar masses from $0.08\ M_\odot$ to $120\ M_\odot$, including post - helium flash evolution and mass loss, model atmosphere libraries also covering late stellar types and giving colours from U to K in agreement with observations and empirical calibrations for a series of absorption indices.

We obtain theoretical calibrations of colours and indices in terms of metallicity which for model ages of 10-15 Gys agree closely with observations of GCs. The theoretical calibrations extend beyond the range of observed GCs, i.e. to a metallicity up to $[M/H] \leq 0.4$.Moreover, our models provide these theoretical calibrations for all ages from cluster formation to 15 Gyrs and thus can also be applied in the interpretation of young star cluster systems observed in many interacting and starburst galaxies.

The complete model files are available via WWW on http://www.uni-sw.gwdg.de/õkurth/ssp.html. There are also models with different parameters for the IMF and for mass loss available.

Acknowledgements

We thank Thibault Lejeune for providing us his library of theoretical stellar spectra, Isabelle Baraffe for providing us with her tracks for the low mass stars and our anonymous referee for valuable and instructive suggestions. This work was supported by the German Deutsche Forschungsgemeinschaft, DFG project number FR 916/3-1.