Improved Measurement of the Rossiter-McLaughlin Effect in the Exoplanetary System HD 17156

TL;DR

This paper provides a more precise measurement of the Rossiter-McLaughlin effect in the HD 17156 system, indicating a well-aligned stellar spin and planetary orbit despite the planet's eccentricity.

Contribution

It offers an improved, high-precision measurement of the spin-orbit angle using Subaru telescope data, correcting previous less accurate estimates.

Findings

Projected spin-orbit angle is approximately 10 degrees.

Stellar spin and planetary orbit axes are likely aligned.

Results suggest a calm dynamical history for the system.

Abstract

We present an improved measurement of the Rossiter-McLaughlin effect for the exoplanetary system HD 17156, based on radial-velocity data gathered with the Subaru 8.2m telescope throughout the planetary transit of UT 2008 November 7. The data allow for a precise and independent determination of the projected spin-orbit angle of this system: $\lambda = 10.0^{\circ} \pm 5.1^{\circ}$. This result supersedes the previous claim of $\lambda = 62^{\circ} \pm 25^{\circ}$ by Narita et al., which was based on lower-precision data with poor statistics. Thus the stellar spin and planetary orbital axes of the HD 17156 system are likely to be well-aligned, despite the planet's large orbital eccentricity suggesting a history of strong dynamical interactions.