Rapid changes in the integrated light of young star clusters

Abstract

We discuss the occurrence of rapid red phases in the integrated colours of star clusters by comparing a colour evolution model with spectral and broad band UBVK observations in the LMC. The model is computed with a very small age step and a fine mass grid of stellar tracks which allow to study the importance of the red supergiant (RSG) phase to the integrated light. This study is based on classical evolutionary tracks for massive stars, but we also infer on the effects of stellar mass loss and internal mixing processes. Taking into account the RSG phase, we find that the model colours are consistent with the observed ones for young clusters (TG < 2 107 yr) if internai reddening in the range 0.1 < E(B- V)< 0.2 is considered.