High wavenumber thermal convection enhanced in regions of partial ionization

Abstract

The linear stability of a compressible hydrogen fluid undergoing thermal ionization is examined. The ionization formulation consistently includes particle number, latent heat and specific heat effects. It is found that the eigenfunctions of the convective modes are strongly peaked in the region of partial ionization. This tendency increases with increasing horizontal wavenumber. In addition, thermal diffusion is least effective in this region due to the increased specific heat of the fluid. Both these effects combine to yield elevated growth rates at high wavenumbers. This work implies the possible existence of shells of very high wavenumber convection embedded in stellar envelopes. Such shells may determine the depth of the peak source of acoustic emission and may mask large scale coherent flows below. Two-dimensional nonlinear simulations are in progress and are briefly discussed as well.