Radiative accelerations of nickel from new monochromatic opacities

Radiative accelerations express the transfer of momentum from the radiation field to the various chemical species of the stellar medium. They are evaluated from the monochromatic cross-sections of each element given the local thermodynamical conditions of the medium. They play an important role in radiative zones because they are involved in the motions caused by atomic diffusion. Depending on the balance with gravity, accumulations or depletions of a given element can appear locally. Wishing to replace the Opacity Project cross-sections for Ni, which come from an extrapolation and are underestimated in layers where the radiative accelerations of Ni are strong, we studied different methods to fit the new cross-sections into the Opacity Project energy grid points. We then compared the radiative accelerations from both sets of data and their effect on stellar structure and on the time evolution of the abundances. The SCO-RCG code was used to produce new monochromatic cross-sections for Ni. The stellar models and evolution were computed with the Toulouse-Geneva evolution code. To fit the new data into the Opacity Project's energy grid, sampling the inverses of the original cross-sections provides the best agreement with the original results . In the Z-bump, the radiative accelerations of Ni have their maximum shifted towards slightly lower temperatures compared to the computation with Opacity Project data. This maximum has a similar amplitude. The radiative accelerations of other species are marginally affected, with no particular impact on the other iron-peak elements. The time evolution of the surface abundances of a 2 M_⊙ star experiences tiny changes, much smaller than the typical observational uncertainty. The inner abundances and mean opacity are also slightly altered in a 9.5 M_⊙ stellar structure, but the pulsation modes that can be excited could change somehow.