Atomic Processes, Theories, and Data For X-Ray Astronomy

Anil Pradhan

Department of Astronomy
The Ohio State University
Columbus, OH 43210

A review of theoretical approximations and experiments for atomic data will be presented. The Close Coupling R-matrix method affords an ab initio and self-consistent treatment of atomic processes on a large-scale: electron impact excitation, photoionization, electron-ion recombination (including both 'radiative' and 'dielectronic' recombination), and transition probabilities. Agreement between experiments and R-matrix results for electron-ion recombination cross sections show that it is possible to calculate rates to 10-20% accuracy, and that there are no significant shortcomings. However, comparison with the distorted wave method and its variants is hampered by lack of availability of detailed cross sections, transition probabilities, and rates for individual atomic transitions over all temperature/density regimes of interest. Such a comparison of fundamental atomic parameters is essential to not only benchmark theories and experiments, but also to ascertain the validity of neglecting or treating indirectly atomic effects such as resonances, fine structure, plasma conditions, etc. Atomic database efforts, including data computed but not yet publicly available, will also be addressed.