Helium diffusion in rapidly oscillating Ap stars

Abstract

Suppression of convection near the poles of magnetic A stars and inhibition of winds near the equator influence chemical composition gradients resulting from diffusion, leading to appreciable horizontal variation in the equilibrium configurations of the stars. We conjecture that it is this variation which is responsible for the apparent alignment of non-radial pulsations with the magnetic axes of the stars, and also for a possible previous misidentification of the modes. We suggest that nonadiabatic excitation can be sufficient to overcome energy leakage into the atmosphere.