Transit timing variation and activity in the WASP-10 planetary system

Abstract

Transit timing analysis may be an effective method of discovering additional bodies in extrasolar systems that harbour transiting exoplanets. The deviations from the Keplerian motion, caused by mutual gravitational interactions between planets, are expected to generate transit timing variations of transiting exoplanets. In 2009, we collected nine light curves of eight transits of the exoplanet WASP-10b. Combining these data with those published, we have found that transit timing cannot be explained by a constant period but by a periodic variation. Simplified three-body models, which reproduce the observed variations of timing residuals, were identified by numerical simulations. We have found that the configuration with an additional planet with a mass of ∼0.1MJ and an orbital period of ∼5.23 d, located close to the outer 5:3 mean motion resonance, is the most likely scenario. If the second planet is a transiter, the estimated flux drop will be ∼0.3 per cent and can be observed with a ground-based telescope. Moreover, we present evidence that the spots on the stellar surface and the rotation of the star affect the radial-velocity curve, giving rise to a spurious eccentricity of the orbit of the first planet. We argue that the orbit of WASP-10b is essentially circular. Using the gyrochronology method, the host star was found to be 270 ± 80 Myr old. This young age can explain the large radius reported for WASP-10b.