Star Cluster Analyses from Multi-Band Photometry: the Key Advantage of SALT's U-band Sensitivity
U. Fritze - v. Alvensleben, P. Anders, T. Lilly
Institute for Astrophysics, Universität Göttingen, Germany
Conventionally, CMD analyses of nearby star clusters are based on observations in 2 passbands. They are plagued by considerable degeneracies between age, metallicity, distance (and extinction) that can largely be resolved by including additional passbands with U being most appropriate for young SCs and I or a NIR band for old globular clusters. For star clusters that cannot be resolved, integrated photometry in useful passbands was shown to be as accurate as spectroscopy in independently revealing ages, metallicities, internal extinction, and photometric masses and their respective 1s uncertainties, when analysed with a dedicated analysis tool for their Spectral Energy Distributions (=SED) (cf. Anders et al. 2003, MN 347, 196+17, de Grijs et al. 2005, MN 359, 874). For external galaxies, rich star cluster populations can thus be imaged and analysed in 4 deep exposures in suitable filters. Again, the inclusion of the U-band significantly reduces the uncertainties in the cluster parameters. The age and metallicity distributions of star cluster systems yields valuable information about the formation history of their parent galaxies (Fritze - v. A. 2004, A&A 414, 515). We present our GALEV evolutionary synthesis models for star clusters of various metallicties (Anders & Fritze - v. A. 2003, A&A 401, 1063), recently extended to include the time evolution of CMDs, the dedicated SED Analysis Tool AnalySED we developed. We show results on the basis of HST data and, hopefully, first results from our SALT PVP projects on young star clusters in starburst and interacting galaxies and on globular clusters in elliptical galaxies.

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