2012A&A...539A.150C

The young G7V dwarf CoRoT-2A is transited by a hot Jupiter and among the most active planet host-stars known to date. We report on the first detection of a chromospheric Rossiter-McLaughlin effect observed in the CaII H and K emission-line cores. In CaII H and K, the transit lasts 15% longer than that observed in visual photometry, indicating that chromospheric emission extends 100000km beyond the photosphere. Our analysis is based on a time series of high-resolution UVES spectra obtained during a planetary transit and simultaneously obtained photometry observed with one of the PROMPT telescopes. The chromospheric Rossiter-McLaughlin effect provides a new tool to spatially resolve the chromospheres of active planet host-stars.