Relativistic close coupling calculations for fundamental atomic processes in astrophysics
Abstract (Summary)The study of fundamental atomic processes has long been one of the most active astrophysical fields. First, we carry out elaborate relativistic atomic calculations of radiative and collisional processes using the Breit-Pauli R-matrix method with one-electron relativistic terms included. We extensively studied low-energy electron impact excitation (EIE) of Fe XVII with emphasis on relativistic and resonance effects. We showed that all N-shell levels give rise to Rydberg resonant states dipping right to M-shell thresholds. These new findings significantly affect the collision strengths for the primary X-ray and EUV transitions among the first 37 levels. We also pointed out the importance of some M2 and E3 multipole transitions in Fe XVII. Accurate X-ray line ratios from strong X-ray lines in Fe XVII were computed and compared with observations. Based on this study and the study of different electron distribution functions in plasmas via collisional-radiative models, two long-standing astrophysical problems of X-ray line intensity ratios 3C/3D and 3s/3d are resolved. The strong energy dependence due to resonances in cross sections was demonstrated. These results are useful for plasma diagnostics in X-ray astronomy. From applications of our Fe VI atomic calculations to planetary nebulae, we developed a method to constrain simultaneously a set of physical conditions. Fluorescent excitation of spectral lines was demonstrated as a function of temperature-luminosity and the distance of the emitting region from the central stars of planetary nebulae. Fluorescence should also be important in the determination of element abundances. We suggested that the method could be generally applied to determine or constrain the luminosity and the region of spectral emission in other luminous sources. We present relativistic close-coupling calculations for unified radiative (RR) and dielectronic recombination (DR), photoionzation and excitation in C IV and Fe XVII. K- and L-shell resonant X-ray absorptions due to O ions and Fe XVI were computed and compared with the Chandra spectra of the Seyfert 1 galaxy MCG—6-30-15. We developed an efficient STGFR code for calculating radiation damping and DR. Next, as the second part of this dissertation, we developed a full Breit-Pauli R-matrix code. We include all the two-electron fine-structure terms, the non-fine-structure spin-spin contact interaction and the two-electron Darwin term.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2004