Internal Gravity Waves Modulate the Apparent Misalignment of Exoplanets around Hot Stars

TL;DR

This paper suggests that internal gravity waves within hot stars can explain the observed misalignment of exoplanets, especially retrograde orbits, by modulating the star's surface rotation.

Contribution

It introduces numerical simulations demonstrating how internal gravity waves can transport angular momentum and affect stellar surface rotation, explaining exoplanet misalignments.

Findings

IGW can modulate surface rotation in hot stars

Simulations explain retrograde exoplanet orbits

Stars may show temporal variations in v sini

Abstract

We propose that the observed misalignment between extra-solar planets and their hot host stars can be explained by angular momentum transport within the host star. Observations have shown that this misalignment is preferentially around hot stars, which have convective cores and extended radiative envelopes. This situation is amenable to substantial angular momentum transport by internal gravity waves (IGW) generated at the convective-radiative interface. Here we present numerical simulations of this process and show that IGW can modulate the surface rotation of the star. With these two- dimensional simulations we show that IGW could explain the retrograde orbits observed in systems such as HAT-P-6 and HAT-P-7, however, extension to high obliquity objects will await future three- dimensional simulations. We note that these results also imply that individual massive stars should show temporal variations in their v sini measurements.