  The herein presented analytical framework 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 behaviour. 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 (e_2<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 satellite. Our results suggest that the formation
history of the systems Kepler-34 and Kepler-413 has most likely been different
from the one 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.
