Analytic orbit propagation for transiting circumbinary planets

The analytical framework presented herein fully describes the motion of coplanar systems consisting of a stellar binary and a planet orbiting both stars on orbital as well as secular timescales. Perturbations of the Runge-Lenz vector are used to derive short-period evolution of the system, while octupole secular theory is applied to describe its long-term behavior. A post-Newtonian correction on the stellar orbit is included. The planetary orbit is initially circular and the theory developed here assumes that the planetary eccentricity remains relatively small (e₂ < 0.2). Our model is tested against results from numerical integrations of the full equations of motion and is then applied to investigate the dynamical history of some of the circumbinary planetary systems discovered by NASA's Kepler spacecraft. Our results suggest that the formation history of the systems Kepler-34 and Kepler-413 has most likely been different from that of Kepler-16, Kepler-35, Kepler-38 and Kepler-64, since the observed planetary eccentricities for those systems are not compatible with the assumption of initially circular orbits.