Stability of circumbinary orbits in misaligned triple star systems

Abstract

We investigate the stability of circumbinary orbits in hierarchical triple star systems, focusing on the effects of a misaligned outer companion star. Test particles are subject to competing gravitational torques from the inner binary and the outer binary companion. With secular theory we estimate the outer radius of particle stability, where the torques balance. We find good agreement with $n$-body simulations across a wide range of triple star configurations. Stable circumbinary orbits can exist even in strongly misaligned triples. Polar and highly inclined orbits with respect to the inner binary can remain stable over a substantial radial range, which is insensitive to the triple star misalignment. Orbits that are close to coplanar or retrograde coplanar to the inner binary are more susceptible to instability when the mutual inclination between the binaries is large. These findings indicate that misaligned and polar circumbinary disks and planets can survive in triple star systems under a broad set of conditions. The analytic criterion identifies where stable material may exist, with implications for the formation and detection of circumbinary planets in multiple-star systems.

Accepted for ApJ