Vol. 588
In section 10. Planets and planetary systems

The Rossiter-McLaughlin effect reloaded: Probing the 3D spin-orbit geometry, differential stellar rotation, and the spatially-resolved stellar spectrum of star-planet systems

by H. M. Cegla, C. Lovis, V. Bourrier, et al. A&A, 588, A127

A planet that transits its host star blocks part of the stellar surface from view, and consequently modifies the integrated spectrum received at Earth. This is known as the Rossiter-McLaughlin (RM) effect and represents a powerful probe of both stellar rotation and the dynamical history of the planetary system. Cegla et al. present a new analysis technique for the RM effect, which instead of modeling the modified integrated spectrum of the star, obtains the spectrum of the occulted section through differencing, and then analyzes its evolution along the transit. Applying this powerful and model-independent new technique to archival observations of the well known HD189733 transiting hot Jupiter system has allowed them to measure both the differential rotation of the star and the 3D relative orientations of the stellar and orbital spins.