L. A. Willson Department of Physics and Astronomy, Iowa State University, Ames, IA 50011
This review stresses four ways that pulsation affects the atmosphere of
a star with consequences for the appearance of the star. These are:
Motion in the form of standing waves, traveling waves, and shocks.
Extension or levitation of the atmosphere.
Heating and cooling of the gas.
The motion is directly observable (at least in some parts of the atmosphere),
and the extension of the atmosphere also produces observable consequences. The
heating and cooling result in part from compression and expansion of the gas,
which keep the low-density gases of the atmosphere out of radiative equilibrium.
In Miras, at least, mass loss is driven by a combination of high pressure produced
by shock-heated gas, momentum imparted by shocks, and radiative forces on dust
grains. Cooling by expansion between shocks provides an opportunity for the
formation of dust to occur close to the star.
All numerical model results presented in this paper are by G. H. Bowen.