Decoupling of a giant planet from its disk in an inclined binary system

¹ Institut für Astronomie und Astrophysik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
e-mail: giovanni.picogna@uni-tuebingen.de
² Dipartimento di Fisica, University of Padova, via Marzolo 8, 35131 Padova, Italy

Received: 23 March 2015
Accepted: 20 August 2015

Abstract

Context. We explore the dynamical evolution of a planet that is embedded in a circumstellar disk, as part of a binary system where the orbital plane of the companion star is significantly tilted with respect to the initial disk plane.

Aims. Our aim is to test whether the planet remains within the disk and continues to migrate towards the star in a Type I/II mode, in spite of the secular perturbations of the companion star. Our findings, could explain why observed exoplanets have significant inclination in relation to the equatorial plane of their host star.

Methods. We used two different smoothed particle hydrodynamic codes, VINE and PHANTOM, to model the evolution of a star+disk+planet system with a companion star over time.

Results. After an initial coupled evolution, the inclinations of the disk and the planet begin to differ significantly. The period of oscillation of the disk inclination, in relation to the initial plane, becomes shorter for the planet, which evolves independently after about 10⁴ yr, following a perturbed N-body behaviour. However, the planet continues to migrate towards the star because, during its orbital motion, it crosses the disk plane, and friction with the gas causes angular momentum loss.

Conclusions. In a significantly inclined binary system, disks and planets are not dynamically coupled for small binary separations but evolve almost independently. The planet abandons the disk, and because of the onset of a significant mutual inclination, it interacts with the gas only when its orbit intersects the disk plane. The drift of the planet towards the star is not due to Type I/II, where the planet is embedded in the disk, but to the friction with the gas while crossing the disk.