Further Observations of the Tilted Planet XO-3: A New Determination of   Spin-Orbit Misalignment, and Limits on Differential Rotation
  We report on observations of the Rossiter-McLaughlin (RM) effect for the XO-3 exoplanetary system. The RM effect for the system was previously measured by two different groups, but their results were statistically inconsistent. To obtain a decisive result we observed two full transits of XO-3b with the Subaru 8.2-m telescope. By modeling these data with a new and more accurate analytic formula for the RM effect, we find the projected spin-orbit angle to be \lambda=37.3 deg \pm 3.0 deg, in good agreement with the previous finding by Winn et al. (2009). In addition, an offset of ~22 m/s was observed between the two transit datasets. This offset could be a signal of a third body in the XO-3 system, a possibility that should be checked with future observations. We also attempt to search for a possible signature of the stellar differential rotation in the RM data for the first time, and put weak upper limits on the differential rotation parameters. 
Teruyuki Hirano, Norio Narita, Bun'ei Sato, Joshua N. Winn, Wako Aoki,   Motohide Tamura, Atsushi Taruya, Yasushi Suto
astro-ph.EP