Effects of Galactic tide on the formation of hot-Jupiters

High eccentricity migration induced by a distant perturber is one of the most promising pathways to the formation of hot Jupiters. In one of the possible scenarios, a distant misaligned stellar companion can excite the eccentricity and inclination of a Jupiter-mass planet through von-Zeipel Kozai Lidov (vZLK) mechanism. The eccentricity excitation allows tidal interactions between the planet and the host star to circularize and shrink the planetary orbit. vZLK mechanism also induces chaotic spin dynamics which produces a broad distribution of spin-orbit misalignment, with peaks at 30 and 130 degrees. Most studies in literature focus on systems in which the stellar companion is on a fixed orbit. In this study, we relax that assumption, and include perturbations due to galactic tides. We study the long term dynamics of such a system under the framework of an adiabatically perturbed hierarchical triple system, since galactic tides operate on timescales much longer than the vZLK timescale. We find that galactic tides are important only for widely separated binaries (> 1500 AU), and that they can increase the efficiency of the formation of hot Jupiters. This is mainly due to the excitation of the eccentricity of the companion by galactic tides, which reduces the vZLK timescale and increases the importance of higher order effects like eccentric vZLK mechanism. In addition, galactic tides can significantly change the distribution of spin-orbit misalignment of hot Jupiters. Instead of a bimodal distribution, we get a distribution which peaks at 90 degrees, similar to the recently discovered excess of close-in perpendicular planets.