Hunting for hot Jupiters around young stars

Hot Jupiters, giant exoplanets similar to Jupiter but with orbits a hundred times tighter than Jupiter's orbit around the Sun, have been detected by the hundreds in the past 24 years, but remain enigmatic objects. While it seems certain that these gas giants form in the outer regions of the protoplanetary disc - the matrix that gives birth to the central star and the surrounding planets - before migrating to the inner regions, the physical process that causes this orbital transfer is still poorly constrained by observations. This question, essential to our understanding of the formation of planetary systems, has profound implications for the architecture of these systems, and in particular for the likelihood of forming planets such as the Earth in the habitable zone of stars. To answer this question, the MaTYSSE consortium has conducted observations of about 30 forming stars to probe the presence of hot Jupiters in their systems. However, young stars are very active, which implies that the strong presence of dark magnetic spots and bright patches on their surface adds a jitter in the measurements, of an amplitude much higher than that of potential planetary signatures. It is therefore necessary to precisely characterize the activity of these stars in order to filter out this perturbation. Following the first detection of a hot Jupiter around a young star using MaTYSSE, this thesis has allowed the characterization of the activity of two other MaTYSSE targets and the detection of a second hot Jupiter around a forming star. These results prove that hot Jupiters can be extremely young and suggest that they migrate rapidly within their protoplanetary disc, and that they are potentially much more frequent around young stars than mature stars like the Sun.