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

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 twodimensional 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 threedimensional simulations. We note that these results also imply that individual massive stars should show temporal variations in their v sini measurements.

Nearly uniform internal rotation of solar-like main-sequence stars revealed by space-based asteroseismology and spectroscopic measurements

“…7) clearly contradicts such reversal. Thus, the present analysis does not support the hypothesis proposed by Rogers, Lin & Lau (2012) as a general picture of F type main-sequence stars.…”

“…Xue et al 2014). In order to explain this phenomenon, Rogers, Lin & Lau (2012) proposed a hypothesis that the near-surface layers of the host star rotate in the opposite direction to the rest of the star, being caused by the angular momentum transport by gravity waves that are generated at the outer boundary of the convective core. Since our analysis simply assumes that all layers of the stars rotate in the same direction about a common axis, the sign change of the rotation rate cannot be measured directly by our analysis.…”

Spin-orbit angle distribution and the origin of (mis)aligned hot Jupiters

“…Along a completely different line of thought, Rogers et al (2012 have proposed the misalignments to arise from the modulation of the outer layers of the host stars by interior gravity waves, rather than relics left behind by the dominant transport mechanism. Cébron et al (2011Cébron et al ( , 2013 also suggest that the excitation of the elliptical instability in the star by the tides raised by the planet could give an apparent tilted rotation axis.…”

Stellar Spin–Orbit Alignment for Kepler-9, a Multi-transiting Planetary System with Two Outer Planets Near 2:1 Resonance

“…These include chaotic star formation (Bate et al 2010;Thies et al 2011;Fielding et al 2015) and evolution (Rogers et al 2012), magnetic torques from host stars (Lai et al 2011), and gravitational torques from distant companions (Tremaine 1991;Batygin et al 2011;Storch et al 2014). In these scenarios, spin-orbit misalignments are expected to be observed not only among star-hot Jupiter pairs, but also among a broader class of planetary systems, notably those that have never experienced chaotic migration processes.…”