  Protoplanetary disks are found around young stars, and represent the
embryonic stage of planetary systems. At different phases of their evolution,
disks may undergo substantial mass-loss by photoevaporation: energetic photons
from the central or a nearby star heat the disk, hence particles can escape the
gravitational potential and the disk loses mass. However, this mechanism, and
the underlying physics regulating photoevaporation, have not been well
constrained by observations so far. The aims of this thesis are to study
photoevaporation, in the specific case when it is driven by far-UV photons, to
identify the main physical parameters (density, temperature) and processes (gas
heating and cooling mechanisms) that are involved, and to estimate its impact
on the disk dynamical evolution. The study relies on coupling observations and
models of disks being photoevaporated by UV photons coming from neighbouring
massive star(s).
