Time-dependent atomic diffusion in the atmospheres of CP stars. A big step forward: introducing numerical models including a stellar mass-loss

Abstract

Calculating abundance stratifications in ApBp/HgMn star atmospheres, we are considering mass-loss in addition to atomic diffusion in our numerical code in order to achieve more realistic models. These numerical simulations with mass-loss solve the time-dependent continuity equation for plane-parallel atmospheres; the procedure is iterated until stationary concentrations of the diffusing elements are obtained throughout a large part of the stellar atmosphere. We find that Mg stratifications in HgMn star atmospheres are particularly sensitive to the presence of a mass-loss. For main-sequence stars with T_{eff}≈ 12 000 K, the observed systematic mild underabundances of this element can be explained only if a mass-loss rate of around 4.2 × 10^{-14} solar mass per year is assumed in our models. Numerical simulations also reveal that the abundance stratification of P observed in the HgMn star HD 53929 may be understood if a weak horizontal magnetic field of about 75 G is present in this star. However, for a better comparison of our results with observations, it will be necessary to carry out 3D modelling, especially when magnetic fields and stellar winds - which render the atmosphere anisotropic - are considered together.