Theoretical models of young open star clusters: Effects of a gaseous component and gas removal

We construct a family of semianalytic models for young open clusters, inclu ding a gaseous component and varying assumptions about the distribution fun ction for the stellar component. The parameters of these models are informe d by observed open clusters and general theoretical considerations regardin g cluster formation. We use this framework to estimate the fraction F-* of the stellar component that remains gravitationally bound after the gaseous component disperses. The remaining stellar fraction F-* is a smooth functio n of the star formation efficiency, epsilon (*), and depends on the distrib ution function of the stars. We calculate the function F-*(epsilon (*)) for this class of open cluster models and provide fitting formulae for represe ntative cases.