Adaptive Optics in High-Contrast Imaging

While most confirmed exoplanets were discovered by indirect techniques such as radial velocities or transits, adaptive optics (AO) assisted direct imaging is a very rich and complementary method that can reveal the orbital motion of the planet, the spectrophotometry of its atmosphere but also the architecture and properties of its circumstellar environment. It can unveil possible interactions with a disc, whether a proto-planetary disc in case of on-going planetary accretion, or a debris disc for more evolved, gas-poor systems. From a statistical point of view, it probes a region, in the mass versus semi-major axis discovery space, different from other techniques, as illustrated in Fig. 2.1. Reaching a uniform sampling of such a parameter space is essential to derive the frequency of planets as a function of mass and semi-major axis, and therefore constrain the planet formation mechanisms. For instance, theories of planet formation predict a higher efficiency of giant planet formation close to the snow line, where radial velocity and transit techniques are poorly sensitive. They require additional ingredients such as migrations and orbital instabilities to explain the current view depicted in Fig. 2.1.