Chromospheres of Cool Non-Mira Giant Stars

Abstract

We review the density and velocity structure of the chromospheres and photospheres of the coolest non-mira M and carbon stars and subject them to the constraints imposed by known mass-loss rates. We note two severe problems. (1) In available chromospheric models, the density falls, within a short distance (< 1 R*) above the photosphere, to less than the density needed to sustain the observed mass loss with the observed flow velocities. To keep the model chromospheric density above the mass-loss value requires large amounts of turbulent energy. (2) Even with reasonable amounts of turbulent energy, densities in all chromospheric models and some photospheric models become so low that mass flow may become significant. In addition, chromospheres are likely inhomogeneous.