The Distribution of Separations of Wide Binaries of Different Ages

Abstract

AbstractFor the purpose of understanding how the distribution of major semiaxes of double and multiple stars has evolved from the earliest ages up to the ages of the oldest systems, we have studied a number of different groups of such systems. We review and expand our previous work on the following groups of stars: (a) The wide binaries in the IDS; (b) Luyten’s common proper motion pairs (the LDS catalogue), (c) Our catalogue of nearby wide binaries divided into two groups: the youngest and the oldest; (d) The common proper motion pairs in the Orion Nebula cluster; (e) Our sample of high velocity, low metallicity binaries that represents a population of very old systems. From the very young binaries (Orion Nebula Cluster) to the oldest (thick disk and halo), all groups show a distribution of major semiaxes following Oepik, i.e., f(a) da ∝ da/a (where a is the major semiaxis), valid over an interval of a between 60 AU and am(t), am(t) being a maximum semiaxis which depends on the age of the binaries as well as on the number density and velocities of the massive objects they encounter as they travel in the Galaxy. Strong gravitational encounters in recently formed multiple systems were found to produce an Oepik distribution, which at small separations (a ≤ 40 − 60 AU) gets truncated by circumstellar disks and close binaries, and at large separations gets depleted by encounters with massive objects.