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Session 19 - Hot Stars.
Display session, Monday, January 15
North Banquet Hall, Convention Center
The heavy elements, platinum, gold, mercury, and thallium, which are apparently overabundant by factors of 10^3--10^5 in many peculiar B stars, also can show strong ionization anomalies, with abundances as determined from different ionization stages differing by as much as 1 dex. It is currently unclear whether such ionization anomalies are simply the result of non-LTE effects, or if they provide evidence for chemical stratification within the photosphere.
To evalulate the expected non-LTE effects, we are constructing model ions for Tl II, Tl III, Hg I, Hg II, and Hg III. Much of the necessary atomic data is being calculated using a combination of accurate, large-scale multi-configurational Dirac-Fock calculations for the most critical transitions, and Cowan code calculations for a larger set of transitions. The resulting statistical equilibrium level populations have been calculated for several of these ions using a model atmosphere of the chemically peculiar star \chi Lupi. We discuss the implications of these calculations for line formation and abundance determinations in \chi Lupi and other peculiar B stars.
Program listing for Monday