Relativistic close coupling calculations for fundamental atomic processes in astrophysics.

摘要

The study and application of fundamental atomic processes, including electron impact excitation, photoionization, radiative recombination and dielectronic recombination of atomic ions and others, has long been one of the most active astrophysical fields in astronomy. First, we carry out elaborate relativistic atomic calculations of radiative and collisional processes for atomic species of astrophysical interest using the Breit-Pauli R-matrix method, in which one-electron relativistic terms are included.; Radiative and electron impact excitation of Fe XVII were calculated. We extensively studied low-energy electron impact excitation of Fe XVII with emphasis on relativistic and resonance effects using the R-matrix code. 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 proved that all previous distorted-wave calculations for Fe XVII with limited isolated resonances used an imprecise method for considering resonance effects. We also pointed out that some M2 (magnetic quadrupole) and E3 (electric octopole) multipole transition probabilities may be too large to be ignored in x-ray spectra and plasma modelling. Accurate X-ray line ratios from 5--6 strong x-ray lines (3C, 3D, 3E, 3F, 3G, M2) in Fe XVII have been 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 theoretically. The strong energy dependence due to resonances in these and other cross sections was demonstrated. These results are useful for plasma diagnostics in x-ray astronomy.; Radiative and electron impact excitation of Fe VI were calculated. From applications of our Few atomic calculations to planetary nebulae (PN) NGC 6741, IC 351 and NGC 7662, we developed a method to constrain simultaneously a set of physical conditions electron density N e, electron temperature Te, luminosity L*, dilution factor W( r)). 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. (Abstract shortened by UMI.)