The impact of environment on the evolution of protoplanetary discs

Protoplanetary discs represent the mass reservoir for planet formation, and the chemicophysical mechanisms occurring during their lifetime sculpt the fundamental properties of the planets born within them. Historically, protoplanetary discs have been initially considered as idealised isolated systems orbiting around a single star. However, recent surveys are showing that both multiplicity and the natal environment can significantly affect disc evolution, since most of stars are born in intermediate-large groups and clusters. Sub-mm surveys of Class 0 objects is compatible with all stars being born in multiple systems. Close binaries (with orbital separation < 40AU) are likely associated to a circumbinary disc, which can be misaligned to the binary plane. Such misalignment leads to a warped structure of the disc. In this thesis, I show that warp evolution in circumbinary protoplanetary discs is well described by simple 1D wave equations, by testing such 1D model with 3D SPH simulations. I also apply the 1D model to transition discs, and show that a massive planet orbiting within the central cavity can be inferred by a small warp in the outer disc, which can be probed by spatially resolved ¹²CO line profiles. The two most relevant environmental mechanisms affecting protoplanetary discs are star-disc encounters, and external photoevaporation. In this thesis, I show that sub-mm observations of the RW Aur system are well described by an ongoing tidal encounter between the circumprimary disc and the secondary star. This makes RW Aur the only system known to date to be undergoing this kind of interaction. I also present new X-Shooter spectral observations of the primary star, which shed a new light in constraining the physical mechanism responsible for the peculiar light curve of the system. Finally, in this thesis I construct a new model of FUV dominated external photoevaporation, extending the parameter space explored in previous literature, and investigating how grain growth affects the mass loss rates.