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Abstract

The charge state distribution of ions of a heavy nuclei species in the stellar plasma environment in which they were formed by s-process nucleosynthesis is investigated. Our aim is to gain insight about the atomic inner-shell electron occupation of heavy elements. The vacancy of the inner shells are of interest when evaluating the role of electronic recombination processes like nuclear excitation by electron capture in s-process nucleosynthesis. To this end we investigate the ionization of osmium (Z=76) as a test case in stellar plasma conditions relevant for the formation of heavy nuclei. For these parameters we derive the ionization states that are formed with the help of the Saha equation. The potential generated by the plasma electrons and ions is treated in the framework of the Fermi model including quantum mechanical corrections. The latter is used to obtain the reduction of the atomic binding energies and the correction of the partition functions due to the plasma particles. Our results predict free K and nearly free L shells for osmium for various plasma parameter sets typical for the s-process sites. These _ndings support the further study of nuclear excitation by electron capture in stellar plasmas, given that the former is strongly facilitated when recombination in inner shells is possible.