  In this PhD Thesis we study the occurrence of powerful stellar outbursts in
the late phases of evolution of stars like the Sun. This is one of the most
controversial topics in the field, as the extraordinary variety of shapes
revealed by observations are not expected to be the result of the evolution of
stars that are basically spherical all over their lives. The stellar ejecta
that we study occur and develop on time-scales of years, even months. This
allows us to study their evolution in real-time. A very rare opportunity in
Astrophysics! To this aim, we have gathered over the years a unique collection
of multi epoch images, from which we produce "movies" that reveal the expansion
of the nebulae as projected in the plane of the sky. Images are complemented by
spectra that measure the line-of-sight velocities, also required to build 3D
models of the dynamical evolution of the outflows, a privileged information for
theoretical modelling.
