Momentum and energy deposition in late-type stellar atmospheres and winds

We have calculated the response of the outer atmospheres of cool, low-gravity stars to the passage of the mechanical energy fluxes of solar magnitude in the form of acoustic waves and Alfven waves. The acoustic (or magnetic fast mode) waves dissipate through shock formation in the low chromosphere; while they can account for the temperature and density structure of chromospheres, such waves have damping lengths that are too short to be effective in driving mass loss. Alfven waves are efficient in generating outflow, and can account for the order of magnitude of observed mass loss in late-type luminous stars. However, unless these magnetic waves undergo some dissipation within several stellar radii of the surface, the predicted terminal velocities of the resulting stellar winds are far too high. Frictional dissipation and the other mechanisms suggest that dissipation may occur, but the magnitude of the effect is not certain. Alfven wave dissipation should give rise to extended warm chromospheres in low-gravity, late-type stars, a prediction which can be observationally tested