A two-step initial mass function: Consequences of clustered star formationfor binary properties

If stars originate in transient bound clusters of moderate size, these clus ters will decay due to dynamic interactions in which a hard binary forms an d ejects most or all the other stars. When the cluster members are chosen a t random from a reasonable initial mass function (IMF), the resulting binar y characteristics do not match current observations. We find a significant improvement in the trends of binary properties from this scenario when an a dditional constraint is taken into account, namely that there is a distribu tion of total cluster masses set by the masses of the cloud cores from whic h the clusters form. Two distinct steps then determine final stellar masses - the choice of a cluster mass and the formation of the individual stars. We refer to this as a "two-step" IMF. Simple statistical arguments are used in this paper to show that a two-step IMF, combined with typical results f rom dynamic few-body system decay, tends to give better agreement between c omputed binary characteristics and observations than a one-step mass select ion process.