Further Observations of the Tilted Planet XO-3: A New Determination of Spin-Orbit Misalignment, and Limits on Differential Rotation

TL;DR

This study refines the measurement of XO-3's spin-orbit angle using new observations and models, confirms previous results, and explores potential additional system components and stellar differential rotation effects.

Contribution

It provides a more accurate determination of XO-3's spin-orbit misalignment and investigates the possibility of differential rotation and additional bodies in the system.

Findings

Projected spin-orbit angle =37.30 b1 3.00

Detected a ~22 m/s offset between datasets, suggesting a potential third body

Placed weak upper limits on stellar differential rotation

Abstract

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.