Techniques for Calculating Radiative Levitation in Stellar Atmospheres
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**Session 7 -- Radiative Transfer and Opacities**
*Display presentation, Monday, 9, 1995, 9:20am - 6:30pm*

## [7.01] Techniques for Calculating Radiative Levitation in Stellar Atmospheres

*C.R.Proffitt (CSC/GSFC), T.Brage (NRC/GSFC), G.M.Wahlgren (CSC/GSFC)*
The extreme abundance and isotopic anomalies found in HgMn stars are usually
assumed to be due to radiative levitation. Diffusion theory makes some
qualitative predictions as to how the radiative force should vary as a function
of depth in the atmosphere in order to explain the observations, but the lack
of atomic data for the elements with the largest anomalies, such as mercury,
platinum, and gold, has prevented the detailed calculations of the line opacity
needed to check this hypothesis.

We have begun to collect the existing atomic data on relevant elements, and
will extend this data base with our own atomic calculations. The high atomic
charge of the elements of interest requires methods that include a careful
treatment of both relativistic effects and correlation. For the bound-bound
transitions that dominate the radiative force, this will require large-scale
multiconfiguration Dirac-Fock calculations.

We are also beginning to develop techniques for using this new atomic data to
perform time-dependant diffusion calculations in stellar atmospheres. We
discuss the observed abundance and isotopic anomalies, the numerical
difficulties which are likely to be encountered, and the use of opacity
distribution functions to simplify the radiative force calculations.

**Monday
program listing**