Radiative accelerations in stars: The effect of Zeeman splitting

The influence of Zeeman splitting on radiative accelerations of chemical elements in stellar atmospheres permeated by magnetic fields with strengths of up to a few Tesla has for the first time been investigated in detail taking into account magneto-optical effects and line blending. The work is based on the newly developed object-oriented and parallel code CARAT (which is presented in some detail), on extensive atomic data taken from the VALD database and on a 12 000 K, log g = 4.0 Kurucz atmosphere with solar abundances. The calculations show that magnetically induced spectral line desaturation can lead to unexpectedly large amplifications of accelerations - relative to the zero-field case - in a number of atomic species. These amplifications are found to be strongly dependent both on field strength and on field orientation, reaching a pronounced maximum near the inclination of 60degr between field vector and vertical with values sometimes in excess of 1.5 dex. Horizontal accelerations, a consequence of polarised radiative transfer, turn out to remain fairly small and will probably not have any important effect on the diffusion velocity vector. This first study on a large scale of how radiative accelerations are affected by Zeeman splitting is completed by a discussion of the importance of complete atomic line lists, in particular line lists with correct Landé factors; it must also be accepted that magneto-optical effects can by no means be neglected. Finally, it appears that the ``canonical'' picture of abundance inhomogeneities may have to be revised: instead of being tied to regions with predominantly vertical or horizontal magnetic fields, abundance patches could show up as contours about the curves tracing the field vector inclination of ~60degr .