  We study the hydrodynamical behavior of the gas expelled by moving Asymptotic
Giant Branch Stars interacting with the ISM. Our models follow the wind
modulations prescribed by stellar evolution calculations, and we cover a range
of expected relative velocities (10 to 100 km/s), ISM densities (between 0.01
and 1 cm-3), and stellar progenitor masses (1 and 3.5 Msun). We show how and
when bow-shocks, and cometary-like structures form, and in which regime the
shells are subject to instabilities. Finally, we analyze the results of the
simulations in terms of the different kinematical stellar populations expected
in the Galaxy.
