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F. Delahaye, M. H. Pinsonneault (The Ohio State University)
Microscopic diffusion processes (such as radiative levitation and gravitational settling/thermal diffusion) in the outer layers of stars are important because they are the source of element segregation that give rise to abundance anomalies observed in hot and slow rotating stars. Radiative levitation is also potentially the physical explanation of the Horizontal Branch morphology as suggested in several recent observations.
Theoretical studies of microscopic diffusion to date have used atomic data from the OPAL group. In this poster we compare radiative accelerations derived from the Opacity Project (OP) with those computed from OPAL data. From prior work, Rosseland mean opacities from the OP and OPAL data are in good agreement except for the high temperature and density regime. Recent enhancements in the atomic data for the Opacity Project have reduced this discrepancy.
Despite the close agreement in \kappaR, the differences in the radiative acceleration (grad) calculated by Michaud et al. using the OPAL and our results using OP data are significantly different.
We present here a detailed comparison of the two data sets, exploring the individual contribution to the mean for each element present in the mixture. Differences in the atomic physics play a role at higher temperatures, but are not large enough to explain the discrepancy in grad.
The change in the resolution between the two databases may also have a significant impact on the computed radiative accelerations/velocities.
Initial calculations in the Sun and other stars are compared with prior results from the literature.
Partial support is provided by CNRS (Observatoire de Meudon).
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.