Radiative accelerations on Ne in the atmospheres of late B stars

Radiative accelerations on Ne are calculated for the atmospheres of main-sequence stars with 11 000 ⩽Teff⩽ 15 000 K. This range corresponds to that of the mercury-manganese (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 non-LTE effects. Non-LTE effects are found to modify the radiative acceleration by a factor of the order of 102 in the outer atmosphere and are crucial for d m < 10−3 g cm−2. The dependence of the radiative accelerations on the Ne abundance, effective temperature and gravity is studied. Radiative accelerations are found to be well below the gravitational acceleration over the entire range of Teff and it is predicted that in stable atmospheres devoid of disturbing motions, Ne should sink and be observed as under-abundant. This agrees with recent observations of low Ne abundances in HgMn stars.