Statistical dynamics of solar-like binaries

A statistical study has been made of dynamic properties of nearby binaries with solar-like primaries, based largely on the 1991 survey of Duquennoy & Mayor. Emphasis is placed on those quantities likely to serve as observational constraints on binary star formation: mass ratios, semimajor axes, orbital angular momenta, and binding energies. Nonparametric statistical models have been employed to deduce statistical distributions of these quantities for those classes of binaries for which individual values cannot be inferred from the observations. There is little correlation observed between semimajor axes and mass ratios or eccentricities, aside from a slight tendency for wide binaries to have low-mass companions and for circularization of close binary orbits. The mass ratio distribution for all binaries in the program is significantly weighted toward low values, with a possible secondary maximum near unity. The distributions of semimajor axes, orbital periods, orbital angular momenta, and binding energies (and their specific forms) all show approximately the same nearly featureless, monotonically decreasing, scale-free form spanning several orders of magnitude; there is no evidence for the presence of more than one population of binaries or of multiple formation mechanisms. The specific angular momenta of binary systems are approximately 2 orders of magnitude less than those of the smallest dense cloud cores from which they presumably form. This, and the distributional form of orbital dynamics, are suggestive of dissipative loss of angular momentum and binding energy, either prior to or after binary formation. Binaries apparently either form by a single mechanism capable of producing orbital scales spanning several orders of magnitude, or are subject to substantial postformation orbital evolution, or both.