Mergers and Obliquities in Stellar Triples

TL;DR

This study uses Monte-Carlo simulations to explore how the eccentric Kozai-Lidov mechanism influences the formation and characteristics of close binaries and mergers in stellar triple systems, highlighting secular dynamics as a key formation channel.

Contribution

It provides the first comprehensive analysis of the impact of EKL on the orbital and spin-orbit configurations of stellar triples, including the role of tides and relativistic effects.

Findings

Approximately 21% of systems form tight binaries via EKL.

About 4% of systems result in mergers, potentially forming blue stragglers.

Spin-orbit angles reflect initial system configurations.

Abstract

Many close stellar binaries are accompanied by a far-away star. The "eccentric Kozai-Lidov" (EKL) mechanism can cause dramatic inclination and eccentricity fluctuations, resulting in tidal tightening of inner binaries of triple stars. We run a large set of Monte-Carlo simulations including the secular evolution of the orbits, general relativistic precession and tides, and we determine the semimajor axis, eccentricity, inclination and spin-orbit angle distributions of the final configurations. We find that the efficiency of forming tight binaries (<~16 d) when taking the EKL mechanism into account is ~ 21%, and about 4% of all simulated systems ended up in a merger event. These merger events can lead to the formation of blue-stragglers. Furthermore, we find that the spin-orbit angle distribution of the inner binaries carries a signature of the initial setup of the system, thus observations can be used to disentangle close binaries' birth configuration. The resulting inner and outer final orbits' period distributions, and their estimated fraction, suggests secular dynamics may be a significant channel for the formation of close binaries in triples and even blue stragglers.