Improved measurement of the Rossiter-McLaughlin effect in the exoplanetary system HD 17156

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 8.2-m 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: λ = 10.°0±5.°1. This result supersedes the previous claim of λ - 62° ±25° by Narita et al. (2008, PASJ, 60, L1), 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. © 2009. Astronomical Society of Japan.