Consistent Evolution of F Stars: Diffusion, Radiative Accelerations, and Abundance Anomalies

Abstract

Consistent stellar evolution models of F stars (1.1È1.5 are calculated with radiative forces, opa-M _) cities, and di †usion for all elements included in OPALÏs opacity tables. The opacities and radiative forces are continuously recomputed during evolution from OPALÏs monochromatic data (D1.5 Gbyte) in order to include all e †ects of abundance changes due to di †usion and nuclear evolution. TOPbase is also used for radiative accelerations. Iron surface overabundances occur in stars more massive than 1.3 Local M _. overabundances of iron peak elements increase the Rosseland opacity in a region at the base of the convection zone by a factor of 3È6 ; this increases the mass of the convective zone by up to a factor of 5. It is important to follow Cr, Mn, and Ni independently of Fe, since they peak at di †erent temperatures within the star. The predicted abundance anomalies are much larger than observed in most F-type stars of open clusters. This suggests that atomic di †usion is not the only process responsible for the Li gap in open clusters. The predicted iron peak element overabundances indicate trends that are compatible with those observed in Fm stars. They however tend to be larger than the observed overabundances, leaving room for some perturbing hydrodynamical process. The present models, devoid of free parameters, are a necessary step in constraining the additional hydrodynamical processes required to better reproduce observed surface abundances. Since the abundances of 28 elements are calculated, one may have 27 constraints on stellar hydrodynamics, once the relative abundances of all species have been determined observationally.