The mean surface density of companions in a stellar-dynamical context

¹ UCO/Lick Observatory, University of California, 499 Kerr Hall, Santa Cruz, CA 95064, USA
² Otto Hahn Fellow, Max-Planck-Institut für Astronomie, Königstuhl 17, 69917 Heidelberg, Germany
³ Sterrewacht Leiden, Postbus 9513, 2300-RA Leiden, The Netherlands
⁴ Institut für Theoretische Physik und Astrophysik, Universität Kiel, 24098 Kiel, Germany e-mail: pavel@astrophysik.uni-kiel.de

Corresponding author: R. S. Klessen, ralf@ucolick.org

Received: 11 July 2000
Accepted: 26 March 2001

Abstract

Applying the mean surface density of companions, , to the dynamical evolution of star clusters is an interesting approach to quantifying structural changes in a cluster. It has the advantage that the entire density structure, ranging from the closest binary separations, over the core-halo structure through to the density distribution in moving groups that originate from clusters, can be analysed coherently as one function of the stellar separation r. This contribution assesses the evolution of for clusters with different initial densities and binary populations. The changes in the binary, cluster and halo branches as the clusters evolve are documented using direct N-body calculations, and are correlated with the cluster core and half-mass radius. The location of breaks in the slope of and the possible occurrence of a binary gap can be used to infer dynamical cluster properties.