A two-step initial mass function:

Consequences of clustered star formation for binary properties

¹ Max-Planck-Institut für extraterrestrische Physik, 85740 Garching bei München, Germany
² Department of Astronomy, SW319, Indiana University, Bloomington, Indiana 47405, USA
³ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
⁴ Department of Physics and Astronomy, Neils Science Center, Valparaiso University, Valparaiso, Indiana 46383, USA
⁵ Department of Chemistry and Physics, Purdue University Calumet, 2200 169th Street, Hammond, Indiana 46323, USA

Corresponding author: R. H. Durisen, durisen@astro.indiana.edu

Received: 4 September 2000
Accepted: 9 March 2001

Abstract

If stars originate in transient bound clusters of moderate size, these clusters will decay due to dynamic interactions in which a hard binary forms and ejects most or all the other stars. When the cluster members are chosen at random from a reasonable initial mass function (IMF), the resulting binary characteristics do not match current observations. We find a significant improvement in the trends of binary properties from this scenario when an additional constraint is taken into account, namely that there is a distribution of total cluster masses set by the masses of the cloud cores from which 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 from dynamic few-body system decay, tends to give better agreement between computed binary characteristics and observations than a one-step mass selection process.