Computer Science – Sound
Scientific paper
Jun 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009phdt.........4l&link_type=abstract
Proquest Dissertations And Theses 2009. Section 0098, Part 0606 268 pages; [Ph.D. dissertation].United States -- Maryland: The
Computer Science
Sound
1
Molecular Fluorescence, Cometary Comae, Sounding Rockets, Planetary Atmospheres, Nebulae, Astronomical Instrumentation
Scientific paper
Understanding the formation and evolution of structure in the universe requires knowledge of the stellar energy output and its processing by gas and dust, evaluating the abundances of atomic and molecular species, and constraining thermodynamic parameters. Molecules, with molecular hydrogen and carbon monoxide being the most abundant, are a major component of the interstellar medium, and play an essential role in structure formation, by participating in gas cooling. Molecular fluorescence studies aim to provide a better interpretation of far-ultraviolet observations, constraining the molecular abundances and their interaction with the radiation field. The fluorescent emission lines offer a set of diagnostics for molecules complementary to absorption line spectroscopy and to observations at infrared and radio wavelengths, but are often poorly reproduced by models. In this work, I have developed and expanded fluorescence models for molecular hydrogen and carbon monoxide, and employed them in determining the spatial distribution of CO in cometary comae, in characterizing the effects of partial frequency redistribution for emission line scattering in planetary atmospheres and reflection nebulae, and in abundance determinations from Bowen fluorescence lines of H 2 in planetary nebulae. Follow-up optical and infrared observations were used in addition to UV data to diagnose molecular excitation, temperature, and spatial distribution in planetary nebula M27.
Knowledge of the spectral energy distribution of the exciting stars in the far- ultraviolet is essential in constraining both the fluorescence models and understanding the scattering properties of nebular gas and dust. Sounding rocket observations of the Trifid and Orion nebulae, performed as part of this work, provided the necessary dynamic range and spatial resolution to measure simultaneously the nebular scattered light and the spectral energy distribution of the illuminating stars. These low extinction sight lines offered a unique view of the intrinsic stellar output below 1200 Å, and an excellent proving ground for the instrument performance. The analysis of these observations using fluorescence and dust scattering models is underway.
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