Diffusion Coefficients in Dense Plasmas

Abstract

It has been known for some time (Schatzman 1958) that diffusion could play an important role in the spectral evolution of white dwarfs. However, it is only recently that quantitative estimates have become available, making use of detailed envelope models (Fontaine and Michaud 1979, hereafter referred to as FM; Vauclair, Vauclair, and Greenstein 1979; Alcock and Illarionov 1979). These studies suggest that the observed monoelemental character of white dwarf spectra can qualitatively be explained in terms of the diffusion model. Moreover, it appears that the diffusion time scales are so short compared to evolutionary times that competing mechanisms, such as accretion, must be invoked to explain the small but measurable abundances of heavy elements in the spectra of cooler white dwarfs.