A Possible Spin-Orbit Misalignment in the Transiting Eccentric Planet HD 17156b

We present simultaneous photometric and spectroscopic observations of HD 17156b spanning a transit on UT 2007 November 12. This system is of special interest because of its 21-day period (unusually long for a transiting planet) and its high orbital eccentricity of 0.67. By modeling the Rossiter-McLaughlin effect, we find the angle between the sky projections of the orbital axis and the stellar rotation axis to be $62^{\circ} \pm 25^{\circ}$. Such a large spin-orbit misalignment, as well as the large eccentricity, could be explained as the relic of a previous gravitational interaction with other planets.

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