  The mass loss properties of carbon AGB stars are not very well constrained at
present. A variety of empirical or theoretical formulae with different
parameterisations are available in the literature and the agreement between
them is anything but good. These simple mass loss prescriptions are nontheless
used in many models of stellar evolution without much consideration of their
applicability in various cases. We present here an on-going project aiming at a
better description of the mass loss, that could be used to improve stellar
evolution models -- especially the evolution during the TP-AGB phase. As a
first step, we have considered the mass loss evolution during a He-shell flash.
Using stellar parameters sampled from a stellar evolutionary track, we have
computed the time evolution of the atmospheric layers and wind acceleration
region during a flash event with detailed frequency-dependent
radiation-hydrodynamical models including dust formation. Based on these
results, we have also simulated the subsequent long-term dynamical evolution of
the circumstellar envelope (CSE), including the formation of a detached shell.
We find that existing simple mass loss prescriptions imply different mass loss
evolutions compared with our model. The second step of the project deals with
the dependence of mass loss on the basic stellar parameters. At the moment we
are computing a large grid of wind models for C-rich AGB stars. Preliminary
results show that simple parameterisations are difficult to obtain in certain
regions of the parameter space considered, due to strong non-linearities in the
wind mechanism.
