2013A&A...556A.134P

Several circumbinary planets have been detected by the Kepler mission. Recent work has emphasized the difficulty of forming these planets at their observed locations due to perturbations by the binary. It has been suggested that these planets formed further out in their discs in more quiescent environments and migrated in to locations where they are observed. We examine the orbital evolution of planets embedded in circumbinary disc models for the three systems Kepler-16, Kepler-34 and Kepler-35. The aims are: to explore the plausibility of a formation scenario in which cores form at large distances from the binaries and undergo inward migration and gas accretion as the gas disc disperses; to determine which sets of disc parameters lead to planets whose final orbits provide reasonable fits to the observed systems. Using a grid-based hydrodynamics code we performed simulations of a close binary system interacting with circumbinary discs with differing aspect ratios, h, and viscous stress parameters α. Once the binary+disc system reaches quasi-equilibrium we embed a planet in the disc and examine its evolution under the action of binary and disc forces. We consider fully-formed planets with masses equal to those inferred from Kepler data, and low-mass cores that migrate and accrete gas while the gas disc is being dispersed. A typical outcome for all systems is stalling of inward migration as the planet enters the tidally-truncated inner cavity formed by the binary system. The circumbinary disc becomes eccentric through interaction with the binary, and the disc eccentricity forces the planet into a non-circular orbit. For each of the Kepler-16b, Kepler-34b and Kepler-35b systems we obtain planets whose parameters agree reasonably well with the observational data, but none of our simulations are able to produce highly accurate fits for all orbital parameters. The final orbital configuration of a circumbinary planet is determined by a delicate interplay between the detailed stucture of the circumbinary disc and the orbital parameters of the planet as it migrates into the inner disc cavity. Simplified simulations such as those presented here provide support for a formation scenario in which a core forms, migrates inward and accretes gas, but accurate fitting of the observed Kepler systems is likely to require disc models that are significantly more sophisticated in terms of their input physics.