AAS 205th Meeting, 9-13 January 2005
Session 7 Laboratory Astrophysics
Poster, Monday, January 10, 2005, 9:20am-6:30pm, Exhibit Hall

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[7.01] Self-consistent and Unified Treatment of Photoionization and Recombination in Astrophysical Sources

S. Nahar, A. Pradhan (Ohio State Univeristy)

Photoionization models of nebular H II regions and active galactic nuclei require a self-consistent treatment of ionization balance between photoionization and electron-ion recombination. However, existing models employ a diverse array of atomic parameters computed in different approximations of varying accuracy. We present new results using the R-matrix method for high precision photoionization and recombination cross sections and rates using exactly the same wavefunction expansion for the electron-ion system. The advantages of the new method are: (i) a computationaly unified treatment of both radiative and di-electronic recombination (RR and DR) in an ab initio manner, (ii) self-consistent calculations for photoionization and recombination using the same wavefunction expansion, (iii) level-specific recombination rate coefficients for a large number of bound levels. These advantages enable a single and accurate total (e-ion) recombination rate coefficient, including RR and DR, to be computed at all temperatures of interest in astrophysical and laboratory plasmas. Shortcomings of methods that treat RR and DR separately are discussed. Computations have been carried out for over 50 atoms and ions, including highly charged Li- and He-like ions of interest in X-ray astronomy; latest results for Ne VIII-IX, Ca XVIII-IX, and Ni XXVI-XXVII are presented. This work was partially supported by the NASA Astrophysical Theory Program.

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