The properties of open cluster binaries based on high-resolution imaging surveys

With known properties such as age, distance and stellar density, young clusters provide ideal samples for binary star studies. We summarize recent results from high-resolution multiplicity surveys of IC 348, a Per, the Pleiades, the Hyades, and Praesepe. The statistics of the resolved companions are used to address binary star formation and evolution in clusters. Over the ranges of ages, densities and stellar masses covered by the clusters, it is found that the binary fraction is correlated with stellar density rather than age, and that both the binary fraction and binary mass ratio distribution depend upon mass. The impact of companions on X-ray emission and stellar rotation is also discussed.