Year of Publication

2006

Document Type

Dissertation

College

Arts and Sciences

Department

Physics and Astronomy

First Advisor

Gary J. Ferland

Abstract

A complete model of helium-like line and continuum emission in astrophysical plasmas has been incorporated into the plasma simulation code CLOUDY. All elements between He and Zn are treated, any number of levels can be considered, and a full treatment of radiative and collisional processes is included. This includes photoionization from all levels, line transfer including continuum pumping and destruction by background opacities, scattering, and collisional processes. The model is calculated self-consistently with the ionization and thermal structure of the surrounding nebula. The result is a complete line and continuum spectrum of the nebula. The model helium atom is described and compared to a second standalone helium atom in the low-density case. The effects of the mixing of singlet and triplet terms, the truncation of the physical system, and the convergence of the predicted line intensities as a function of the number of quantum levels explicitly included are considered. New Case-B emissivities are calculated for the helium atom at a range of electron temperatures and densities common in planetary nebulae. Observations of the Orion Nebula are analyzed and compared with predictions of the model helium atom. Observations of low-metallicity extragalactic objects by other authors are analyzed. The methods and details of the model helium-like ions are described. The standard X-ray diagnostics of these ions are revisited and augmented with semi-analytical and numerical calculations of ultraviolet line diagnostics. Finally, a new interface between CLOUDY and the X-ray spectral analysis tool XSPEC is discussed.

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