Transit mapping of a starspot on CoRoT-2

Probing a stellar surface with planetary transits

¹ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: [uwolter;jschmitt]@hs.uni-hamburg.de
² Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: [guenther;artie]@tls-tautenburg.de

Received: 14 April 2009
Accepted: 17 June 2009

Abstract

We analyze variations in the transit lightcurves of CoRoT-2b, a massive hot Jupiter orbiting a highly active G star. We use one transit lightcurve to eclipse-map a photospheric spot occulted by the planet. In this case study we determine the size and longitude of the eclipsed portion of the starspot and systematically study the corresponding uncertainties. We determine a spot radius between and  on the stellar surface and the spot longitude with a precision of about  degree. Given the well-known transit geometry of the CoRoT-2 system, this implies a reliable detection of spots on latitudes typically covered by sunspots; the size of the modelled spot is comparable to large spot groups on the Sun. We discuss the future potential of eclipse mapping by planetary transits for the high-resolution analysis of stellar surface features.