Presentation #401.03 in the session Exoplanet Dynamics 2: Stellar and Planetary Obliquities.
Many hot Jupiters (HJs) have been observed to have large obliquities or misalignments between the stellar spin axis and the orbital angular momentum of the planet. This observation hints that at least a portion of HJs formed through high-eccentricity migration, in which a cold Jupiter is excited onto a highly eccentric orbit that circularizes over time due to tidal dissipation in the planet. One variety of high-e migration occurs when eccentricity oscillations are excited by an inclined stellar companion (von Zeipel-Kozai-Lidov, or ZKL oscillations). Previous population studies of this mechanism assumed initial spin-orbit alignment. However, a star’s obliquity may be significantly excited during the dissipation of its protoplanetary disk. By using a disk-excited obliquity for the initial condition of a new population synthesis, we demonstrate that the expected obliquity distribution from ZKL-driven high-e migration has a peak near 90 degrees, similar to the recently-observed preponderance of perpendicular planets close to their host stars.