The Frequency Distribution of Major Semiaxes of Wide Binaries: Cosmogony and Dynamical Evolution

The frequency distribution f(a) of major semiaxes of double and multiple systems, and their eccentricities and mass ratios, contain valuable fossil information about the process of star formation and the dynamical history of the systems. In order to advance in the understanding of these questions, we made an extensive analysis of the frequency distribution f(a) for wide binaries (a > 25 AU) in various published catalogues, as well as in our own (Poveda et al. 1994; Allen et al. 2000; Poveda & Hernández-Alcántara 2003). Based upon all these studies we have established that the frequency distribution f(a) is function of the age of the system and follows Oepik’s distribution f(a) ∼ 1/a in the range of 100 AU < a < ac(t), where ac(t) critical major semiaxis beyond which binaries have been dissociated by encounters with massive objects. We argue that the physics behind the distribution f(a) ∼ 1/a is a process of energy relaxation, analogous to those present in stellar clusters (secular relaxation) or in the early stages of spherical galaxies (violent relaxation). The existence of runaway stars indicates that both types of relaxation are important in the process of binary and multiple star dynamical evolution.