Origin of the Break and Mass-Dependence in the Wide-Binary Projected-Separation Distribution

Abstract

The distribution of Galactic-disk wide binaries shows a clear break in slope at projected separations of about r_\perp ~ 2500 AU in two basically independent surveys by Chaname & Gould and Lepine & Bongiorno. The latter also showed that the frequency of wide-binary companions to G-star primaries declines monotonically as a function of companion mass. We show that both effects can be explained by the operation of Heggie's law in the typical open-cluster environments where binaries form. One immediate conclusion is that most Galactic-disk stars formed in open clusters with internal dispersions of a few hundred meters per second and disruption times of a few hundred million years.

submitted to ApJ Letters, 4 pages + 1 figure