Orbital Eccentricity Distribution in Binary Systems

In this paper, we discuss the orbital eccentricity distribution for 143 early-type and 125 late-type binary systems. By dividing these samples into main-sequence, giant and particular binary groups, we find that the degree of orbital circularization in giant binaries is averagely higher than that in corresponding main-sequence systems, and that there exists a limiting orbital period below which orbital circularization(e≤0.05) can be regarded as a rule in each group. The limiting P is about 1.7d in early-type main-sequence binaries, 2.0d and 7.5d respectively for early-type giant and particular binary systems, whereas the late-type main-sequence and giant binary systems have the limiting P of about 7.0d and 10.0d respectively. Analyzing the obtained statistical relations and theoretical predictions on circularization, we find that the predictions of dynamically and equilibrium tidal mechanisms fit observational data better than that by using the purely hydrodynamic theory.