A Possible Tilted Orbit of the Super-Neptune HAT-P-11b

TL;DR

This study detects a significant spin-orbit misalignment in the super-Neptune exoplanet HAT-P-11b, indicating it likely underwent dynamical processes like scattering or Kozai migration, which are common in eccentric exoplanet systems.

Contribution

First measurement of the Rossiter-McLaughlin effect for HAT-P-11b revealing a tilted orbit, expanding understanding of spin-orbit dynamics in super-Neptune exoplanets.

Findings

Detected a projected spin-orbit misalignment angle of approximately 103 degrees.

Supported the idea that eccentric exoplanets often have significant orbital tilts.

Suggested dynamical interactions influence the orbital evolution of super-Neptunes.

Abstract

We report the detection of the Rossiter-McLaughlin effect for the eccentric, super-Neptune exoplanet HAT-P-11b, based on radial velocity measurements taken with HDS mounted on the Subaru 8.2m telescope, and simultaneous photometry with the FTN 2.0m telescope, both located in Hawai'i. 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 $\lambda= 103_{-19}^{+23}$ deg. Our result supports the notion that eccentric exoplanetary systems are likely to have significant spin-orbit misalignment (e.g., HD 80606, WASP-8, WASP-14, WASP-17, and XO-3). 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 the Kozai migration.