Properties of unresolved star clusters: the effect of Stochastic Fluctuations

by Morgan Fouesneau (Strasbourg Observatory)

Friday 20 Nov 2009, 10:30 → 12:00 Europe/Stockholm

Star clusters have become our main tracer of the histories of galaxies while providing precious constraints on stellar physics. It has become clear that a significant fraction of stars form in clusters, and that events such as galaxy interactions can trigger their formation. Resolved observations of individual stars remain the most precise ways of investigating the nature of stellar clusters out to distances of 10Mpc (next generation telescopes). However measurements of the integrated light of unresolved star clusters reach far beyond and remain the path of choice for studying large samples. All our studies of cluster populations in galaxies rest on our ability to estimate their current ages, masses and metallicities. During this presentation, I will discuss the current commonly used estimation method, limited in particular because they do not account for the fact that cluster light is dominated by a relatively small number of bright stars. Comparing this method to a Bayesian approach, which account for the fluctuations of this number of bright dominant stars, I will present some systematics introduced by the classical method.