  A significant step forward in the understanding of Planetary Nebula (PN)
formation can be achieved by exploring the connection of PN with stellar
evolution. In particular, the initial mass of the star plays a crucial role, as
it determines the evolutionary timescales, the density structure of the gas and
the amount of energy injected into the nebula. Here we summarize our study of
the effects of stellar mass in PN formation. Our numerical simulations include
the evolution of the stellar wind for different initial progenitor masses and
the influence of the ISM. We also investigate how the systemic velocity of the
star with respect to its surrounding medium affects the PN formation. We find
that unless the star is moving, most of the mass lost by PN progenitors can be
found in the low surface brightness extended halos, where the stellar ejecta is
mixed with ISM material. For a moving central star, the interaction with the
ISM considerably reduces the mass of the circumstellar envelope during the AGB
and PN phases owing to ram pressure stripping.

Astrophysics