Chromospheric velocity fields in α Orionis (M2 Iab) generated by stochastic shocks

I present results from recent ab-initio models for the formation and time-dependent behavior of outer atmospheric flows in α Ori (M2 Iab) produced by stochastic shock waves. Stochastic shocks are a natural consequence of acoustic energy generation due to stellar convection. Thewavemodels showdistinct episodes ofmomentum and energy deposition produced by strong shocks generated by merging of shocks in the stochastic wave field. It is found that suband supersonic inflows and outflows are generated at different atmospheric heights as function of the wave parameters adopted. The flow velocities given by the models encompass the velocity range revealed by the Fe II emission line components given by recent GHRS data (Carpenter & Robinson 1997). This result is evidence that nonmagnetic wave modes are relevant for the heating and dynamics of the outer atmosphere of α Ori and possibly other M-type supergiants as well, although it does not preclude the possibility that magnetic heating may be equally or more important.