Davey, Alisdair Richard; (1995) The recombination spectrum of Carbon II. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The determination of the physical parameters of various astrophysical plasmas requires accurate calculation of the radiative and collisional processes involved. The recombination spectrum of Carbon II lends itself to investigating regions such as gaseous nebulae and low temperature stellar winds. In this thesis, a detailed treatment of the recombination processes of CII has been carried out, covering a wide range of temperatures and densities. Accurate photoionisation calculations, using the R-matrix solution to the close coupling equations have been performed. In the process, bound state energy levels have been determined and new weighted oscillator strengths calculated, over a larger range and with a greater accuracy, than had been previously achieved. With careful attention to resonances, which dominate the recombination at low temperatures, recombination coefficients have been evaluated for all states up to n = 15, L = 4. As well as radiative processes, all important collisional processes have been included, creating a full collisional-radiative-cascade model, in order to determine the populations of the states of CII at varying temperatures and densities. Detailed comparison with previous theoretical work has been made. The application of the CII recombination spectrum to the observed spectra of two contrasting astrophysical plasmas such as cold nova shells and Wolf-Rayet stellar winds is considered. The usefulness and applicability of the CII recombination spectrum as a diagnostic tool is ably demonstrated.

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