The short-period exoplanet HD 147506b (also known as HAT-P-2b) has an eccentric orbit, raising the possibility that it migrated through planet-planet scattering or Kozai oscillations accompanied by tidal dissipation. Either of these scenarios could have significantly tilted the orbit relative to the host star's equatorial plane. Here we present spectroscopy of a transit of HD 147506b, and assess the spin-orbit alignment via the Rossiter-McLaughlin effect. We find the sky projections of the stellar spin axis and orbital axis to be aligned within 14 deg. Thus we find no corroborating evidence for scattering or Kozai migration, although these scenarios cannot be ruled out with the present data.
@article{arxiv.0707.0503,
title = {Spin-Orbit Alignment for the Eccentric Exoplanet HD 147506b},
author = {Joshua N. Winn and John Asher Johnson and Kathryn M. G. Peek and Geoffrey W. Marcy and Gaspar A. Bakos and Keigo Enya and Norio Narita and Yasushi Suto and Edwin L. Turner and Steven S. Vogt},
journal= {arXiv preprint arXiv:0707.0503},
year = {2009}
}