Modeling Stellar Populations in Star Clusters and Galaxies

Combining population synthesis models with simple Montecarlo simulations of stochastic effects in the number of stars occupying sparsely populated stellar evolutionary phases in the HRD, I show that the scatter observed in the photometric magnitudes and colors of LMC and NGC 7252 star clusters can be understood in the framework of current stellar evolution theory. The use of a high resolution stellar spectral atlas in population synthesis models improves considerably the quality of the fits to observed galaxy SEDs, making the assignment of a spectroscopic age to stellar populations more reliable than with low spectral resolution models.