THE ROLE OF (SUB-)STELLAR COMPANIONS ON THE DYNAMICAL EVOLUTION OF PROTOPLANETARY DISCS

The study of planet formation has become progressively more important in the last few years given the great number of diverse exoplanets recently discovered. It is, indeed, only by studying extrasolar planetary systems embedded in their natal (protoplanetary) discs that we can make statistical studies of the range of outcomes of the planet formation process. In particular, the discs that present a cavity (transitional discs) or a gap in the dust radial profile are related to disc clearing mechanisms by young giant planets. In this Thesis, we analyze observations taken with the most advanced telescopes (ALMA and VLT/SPHERE) combining multi-wavelength observations to discriminate between different formation processes in systems with disc sub-structures. We provide a general overview on protoplanetary discs and planets/binaries, followed by the description of dust and gas dynamics and thermal disc structure. Moreover, we describe the two most accredited scenarios of planet formation: core accretion and gravitational instability. In the second part of the Thesis, we present a work on the dust and gas cavity of the disc around CQ Tau observed with ALMA together with thermochemical models and hydro-dynamical simulations, which provide insight on a massive planet responsible for the clearing of such disc structure. Secondly, we describe an analysis done on a survey of 22 Herbig and F/G type stars imaged by SPHERE that confirms that the large near-infrared excess observed in the SEDs of Group I Herbig stars can be explained by the presence of a large gap in their discs. We spatially resolve spirals in HD 100453, HD 100546, CQ Tau; ring-like disc in HD 169142 and HD 141569; and single inclined thin disc in AK Sco and T Cha. We compare the results with ALMA and PDI observations and with simulations. Moreover, we detect and confirm the presence of a novel gravitationally bound companion to the young MWC 297 star. Finally, we describe a novel routine that exploits the known radial variation of stellar artifacts with wavelength together with the spectral slope of the star.