Generation of Mass Loss in K Giants: The Failure of Global Oscillation Modes and Possible Implications

Abstract

It is a well-established observational result that many inactive K stars show global oscillation modes, which lead to low-amplitude photospheric velocity variations. It is the purpose of this paper to investigate whether these modes are relevant to the outer atmospheric dynamics, including the generation of mass loss. We find that this is not the case as most of these modes remain evanescent ('mode trapping'). Nonlinear effects are negligible as the wave amplitudes remain very small. The failure of these modes to produce mass loss (as well as the failure of acoustic modes previously studied) should be considered as strong evidence that the mass loss in these stars cannot be initiated by a nonmagnetic process. This result is of particular interest as the chromospheric heating in most of these stars seems to be fully attributable to acoustic energy dissipation.