Radiative accelerations in stars: The effect of Zeeman splitting

Abstract

The influence of Zeeman splitting on radiative accelerations of chemical elements in stellar atmospheres permeated by magnetic elds with strengths of up to a few Tesla has for the rst time been investigated in detail taking into account magneto-optical eects 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, logg =4 :0 Kurucz atmosphere with solar abundances. The calculations show that magnetically induced spectral line desaturation can lead to unexpectedly large amplications of accelerations { relative to the zero-eld case { in a number of atomic species. These amplications are found to be strongly dependent both on eld strength and on eld orientation, reaching a pronounced maximum near the inclination of 60 between eld 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 eect on the diusion velocity vector. This rst study on a large scale of how radiative accelerations are aected by Zeeman splitting is completed by a discussion of the importance of complete atomic line lists, in particular line lists with correct Land e factors; it must also be accepted that magneto-optical eects 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 elds, abundance patches could show up as contours about the curves tracing the eld vector inclination of60.