Comparison of radiative accelerations obtained with atomic data from OP and OPAL

Microscopic diffusion processes (such as radiative levitation and gravitational settling/thermal diffusion) in the outer layers of stars are important because they may give rise to surface abundance anomalies. Here, we compare radiative accelerations (grad) derived from the new Opacity Project (OP) data 1 with those computed from OPAL and some previous data from OP. For the case where we have full data from OPAL (carbon, 5 points in the ρ−T plane), the differences in the Rosseland mean opacities between OPAL and the new OP data are within 12% and less than 30% between new OP and previous OP data (OP1) . The radiative accelerations grad differ at up to the 17% level when compared to OPAL and up to the 38% level when compared to OP1. The comparison with OP1 on a larger (ρ−T ) space gives a difference of up to 40% for grad(C). And it increases for heavier elements. The differences increase for heavier elements reaching 60% for Si and 65% for S and Fe. We also constructed four representative stellar models in order to compare the new OP accelerations with prior published results that used OPAL data. The Rosseland means overall agree better than 10% for all of our cases. For the accelerations, the comparisons with published values yield larger differences in general. The published OPAL accelerations for carbon are even larger relative to OP compare to what our direct comparisons would indicate. Potential reasons for this puzzling behavior are discussed. These data will be made generally available via a server or on CDROM. All request should be sent to Claude Zeippen ([email protected]), or to Anil Pradhan ([email protected]). The OP1 data are the data present in the database at Centre de Données de Strasbourg (CDS, http://cdsweb.u-strasbg.fr/).