Diffusion of Silicon in the Envelopes of Hot DA White Dwarfs

Abstract

White dwarf stars are expected to have peculiar elemental abundances in their superficial layers because of their high gravities and thin atmospheres. The gravitational settling, if left unimpeded, is so efficient in these stars that it very rapidly depletes the atmosphere of its heavy element content, leaving only the lightest elements: hydrogen or helium. The detection of traces of heavy elements in the atmospheres of white dwarfs, however, clearly implies that some mechanisms must be at work to counteract the effects of downward settling.