A Robust Measure of Tidal Circularization in Coeval Binary Populations: the Solar-Type Spectroscopic Binary Population in the Open Cluster M35

摘要

We propose a new and robust diagnostic of the degree of tidal circularization in a binary population based on a functional fit to the distribution of orbital eccentricity vs. orbital period (e — log(P)). We call this new measure the tidal circularization period. The tidal circularization period of a binary population represents the orbital period at which a binary orbit with the most frequent initial orbital eccentricity circularizes (defined as e = 0.01) at the age of the population. We present the e — log(P) distribution for a new homogeneous sample of 32 spectroscopic binary orbits in the young 150 Myr) main-sequence open cluster M35. The distribution displays a distinct transition from eccentric to circular orbits that provide a significantly improved constraint on the rate of tidal circularization at an age of 150 Myr. We determine the tidal circularization period for M35 as well as for 7 additional binary populations spanning ages from the pre main-sequence 3 Myr) to late main-sequence (-10 Gyr), and use Monte Carlo error analysis to determine the uncertainties on the derived circularization periods. We conclude that current theories of tidal circularization cannot account for the distribution of tidal circularization periods with population age.