Radiative accelerations in stars: The effects of magnetic polarisation revisited

We present a revision of the results obtained by Alecian & Stift (2002) on the amplification, by Zeeman splitting in strong stellar magnetic fields, of radiative accelerations of chemical elements. These results had been obtained for blended spectra and were based on the Zeeman Feautrier method as presented by Rees et al. (1989) which however requires perfect symmetry of the line profiles. The use of this method in an inappropriate context led to the incorrect identification of those line absorption terms which change sign for the incoming radiation. The question of magnetic amplification of radiative accelerations had to be revisited. Following the formulation of an alternative Zeeman Feautrier scheme which remains valid for blends (albeit only when macroscopic velocity fields are excluded), the resulting radiative accelerations are now less amplified than what had been found in Alecian & Stift (2002). In a 12 000 K, log g = 4.0 Kurucz atmosphere with solar abundances, amplifications at a field strength of 4 T peak at about 0.4 dex, and there is very little dependence on the field inclination. Depending on the Zeeman pattern, individual lines may exhibit amplifications of more than 1.1 dex. Blending is found to greatly affect radiative accelerations but not amplifications; only in exceptional cases such as for Ag can strong blending lead to an inversion of the amplification, i.e. accelerations actually decrease with increasing field strength. Finally magneto-optical effects continue to be non-negligible, horizontal accelerations remain small.