91福利

Atomic diffusion is usually a slow and negligible process in stellar interiors. However, in the radiative, still H-envelopes of subdwarf B stars, diffusion acts quickly and causes dramatic abundance changes. For example, iron-group elements are radiatively levitated in the H-envelope, which can drive stellar pulsations via the opacity-mechanism. Also, observed sdB abundance anomalies are attributed to atomic diffusion, although the chemical peculiarities cannot be explained by diffusion theory alone. Both mass-loss and turbulence have been invoked to slow down atomic diffusion in order to match observed abundances. The presence of stellar pulsations gives upper limits on the amount of mass-loss and turbulent mixing allowed, at least for the pulsators. We use non-adiabatic asteroseismology to decide if mass-loss or turbulence could be responsible for sdB abundance anomalies.