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, including a gaseous component and varying assumptions about the distribution function for the stellar component. The parameters of these models are informed by observed open clusters and general theoretical considerations regarding 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 function of the star formation efficiency, epsilon (*), and depends on the distribution function of the stars. We calculate the function F-*(epsilon (*)) for this class of open cluster models and provide fitting formulae for representative cases.