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Georgia Journal of Science

Article Title

ABUNDANCES AND IONIZATION EQUILIBRIUM SOLUTIONS OF BROMINE, RUBIDIUM, AND XENON IN ASTROPHYSICAL NEBULAE**

Abstract

To compute highly accurate Br, Rb, and Xe abundances in ionized astrophysical nebulae, we have computed large grids of numerical simulations to investigate the ionization equilibria of these elements. Br, Rb, and Xe are neutron(n)-capture elements (atomic number Z > 30), which are of particular interest in planetary nebulae (PN) since they can be produced during the red giant stage of low-mass (1-8 solar mass) stars. Therefore if a PN progenitor star experienced n-capture nucleosynthesis, trans-iron elements are expected to have enhanced abundances, which can be used to infer poorly-understood physical properties of red giant stars (e.g., interior structure, convection, and mixing processes). However, only 1-2 ions of n-capture elements are typically detected in individual nebulae, and analytical “ionization correction factors” (ICFs) must be utilized to correct for unobserved ions and compute elemental abundances. To derive ICFs for Br, Rb, and Xe, we have have modified the state-of-the-art nebular modeling code Cloudy to include these elements, using recently determined atomic data for photoionization and recombination processes. We computed large grids of Cloudy models, spanning the range of physical parameters of PN, including central star temperature and luminosity, nebular density, chemical composition, and dust chemistry. We derive ICFs by identifying correlations between the fractional abundances of observed Br, Rb, and Xe ions with those of commonly detected ions of lighter species (e.g., He, O, S, Cl, and Ar). The ICFs have been used to compute Br, Rb, and Xe abundances to unprecedented accuracy in PN.

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