Radiative accelerations on Ne in the atmospheres of late B stars

Abstract

Radiative accelerations on Ne are calculated for the atmospheres of main sequence stars with 11000 < Teff < 15000 K, corresponding to the range of the HgMn stars. The calculations take into account neon fine structure as well as shadowing of neon lines using the entire Kurucz line list, bound-bound, bound-free, and free-free opacity of H, He, and C as well as some NLTE effects. NLTE effects modify the radiative acceleration by a factor of order 100 in the outer atmosphere. The dependence of the radiative acelerations on the Ne abundance, Teff, and gravity is studied. Radiative accelerations are well below gravity in the entire range of Teff and it is predicted that in stable atmospheres Ne should sink and be observed as underabundant. This agrees with recent observations of low Ne abundances in HgMn stars.