A Turbulent Interstellar Medium Origin of the Binary Period Distribution

Abstract

We present a semiempirical model of isolated binary star formation. This model includes the effects of turbulence in the initial state of the gas and has binary orbital parameters consistent with observation. This model therefore provides a framework with which to examine the relative importance of turbulence in the context of isolated binary star formation and to make quantitative predictions to compare against observation. The primary results of this model are as follows: (1) a quantitative prediction of the initial width of the binary period distribution (σlog Pd= 1.6-2.1 for a star formation efficiency in the range ε* = 0.1-0.9), (2) a robust anticorrelation of binary period and mass ratio, (3) a robust, positive correlation of binary period and eccentricity, and (4) a robust prediction that the binary separation of low-mass systems should be less than that of solar-mass or larger systems. These predictions are in good agreement with observations of pre-main-sequence binary systems with periods of P > 10 3 days, which account for the majority of all binaries. We conclude with a brief discussion of the implications of our results for observational and theoretical studies of multiple star formation.