A possible tilted orbit of the super-Neptune HAT-P-11b

Abstract

We report on the detection of the Rossiter-McLaughlin effect for the eccentric, super-Neptune exoplanet HAT-P-11b, based on radial-velocity measurements taken with the High Dispersion Spectrograph mounted on the Subaru 8.2m telescope, and simultaneous photometry with the LCOGT 2.0m Faulkes Telescope North, both located in Hawaii. The observed radial velocities during a planetary transit of HAT-P-11b show a persistent blue-shift, suggesting a spin-orbit misalignment in the system. The best-fit value for the projected spin-orbit misalignment angle is λ = 103°+22°-18° . This fact suggests that not only hot-Jupiters, but also super-Neptunes like HAT-P-11b had once experienced dynamical processes, such as planet-planet scattering or Kozai migration.