REFLECTION OF ALFVEN WAVES IN STELLAR ATMOSPHERES - THE CASE OF OPEN MAGNETIC-FIELDS

We investigate the basic properties of reflection and transmission of Alfven waves in a radially inhomogeneous, magnetized, and ''open'' late spectral type stellar atmosphere. We have obtained analytic solutions for the limiting cases of large and small distances above the stellar surface and have obtained numerical solutions for all radii over the entire frequency range of interest in such atmospheres. Our key result is that while Alfven wave trapping in a stratified atmosphere with open magnetic fields may not be very effective in solar coronal holes, it can be very effective in the magnetized outer atmospheres of giant and supergiant stars. This result supports earlier conjectures that Alfven wave reflection may be in part responsible for the driving of massive winds in the atmospheres of late-type giants and supergiants.