Abstract

Twenty years after the first discovery of an extrasolar planet orbiting a solar-type star, the present exoplanet harvest now exceeds 1900 planets, of which over 1250 are transiting. These transiting planets are of particular interest as their special geometric configuration provides us with a unique opportunity to study their structural, orbital, and atmospheric properties. Large photometric transit surveys very often need follow-up photometry of their candidates at higher spatial/temporal resolution and higher precision to confirm new detections and determine precisely the parameters of the discovered systems. In this context, I will first present the photometric follow-up program of transit surveys that is carried out on the 0.6m TRAPPIST robotic telescope and its main results in five years of operation. I will then describe the discovery and remarkable physical properties of the WASP -121 planetary system, one of the many planetary systems co-detected with TRAPPIST . I will conclude with some results of an intensive photometric campaign aiming to probe the emission spectrum of the extreme hot Jupiter WASP -103b using TRAPPIST , and the 1.2-m Euler/EulerCam and 3.6-m CFHT /WIRCam instruments.