Title from PDF of title page (University of Missouri--Columbia, viewed on Feb. 18, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dr. Rainer Glaser, Thesis Supervisor. Includes bibliographical references.

Molecular formation and destruction processes are explored in rapidly evolving, non-equilibrium astrophysical environments. First, a semi-classical calculation is made for the rate coefficients of excited atom radiative association to form molecular hydrogen and of the process C⁺ + O → CO⁺ + hν. The latter process may be important to the formation of CO in the core of Supernova 1987A. It is shown that the excited atom process may have been important to the formation of H$\sb2$ during the early part of the epoch of recombination in the early Universe. The equations of ionization balance and molecular formation and destruction have been integrated through the epoch of recombination. Other processes are examined in detail. These include heating and cooling of the primordial plasma, damping of fluctuations prior to decoupling, and the possibility of a radiation-driven instability at the onset of recombination. A calculation is presented of the time-dependent chemical evolution in the rapidly expanding outer envelope of SN 1987A. Various cooling rates and hydrogen abundances in the envelope have been examined. It is found that large molecular abundances, in particular CO, form rapidly, while hydrogen remains mostly in its atomic forms. Near-infrared observations of the proto-planetary nebula CRL 618 are presented and discussed. Images acquired in the H and K bandpasses are consistent with a bipolar axis highly inclined to the plane of the sky. From the spectrum, a visual extinction of Aᵥ = 5.3 magnitudes to the molecular hydrogen emitting lobes is found. It is shown by comparison with spectral models that the near-infrared H₂ spectrum exhibits emission from thermally excited molecules at Tₑₓ ∼ 2000 K. A component of fluorescent emission may also be present. The suggestion is explored that large molecules, in particular polycyclic aromatic hydrocarbons (PAHs), are formed in stellar winds. It is asserted that the primary source of interstellar PAHs is mass-losing asymptotic giant branch carbon stars. It is apparent that the known numbers of the most extreme mass-losing carbon stars are able to produce PAHs in sufficient quantities to maintain an interstellar medium well mixed in such molecules at the inferred abundance.

The total luminosity of the Rho Ophiuchi molecular cloud is derived from IRAS data and is found to match the luminosity of known embedded sources very closely. High resolution 60 and 100 micron band IRAS images have been reduced to yield equilibrium color temperature maps and 60 micron band dust optical depth maps for the region. These data along with optically thin C18O column density data are used to evaluate dust grain sizes and compositions via competing grain models. Radiative modeling shows that a standard power law distribution of graphite and silicate grains is responsible for IRAS 60 and 100 micron band emissions. These grains are heated to about one tenth of the cloud's depth in the core region. Their optical depths closely follow molecular column density structure, but these grains are considerably colder than the molecular gas. We also find that a 10 nm minimum particle radius cutoff is appropriate for the 60 and 100 micron band emissions while very small grains or PAH molecules dominate the cloud's 12 and 25 micron band emissions.

No description available.

Thesis (Ph. D.) -- California Institute of Technology, 2010. / Title from home page (viewed 2/25/2010). Advisor and committee chair names found in the thesis' metadata record in the digital repository. Includes bibliographical references.

During the first billion years after the big bang, the large-scale cosmic web of structures we see today began to form. This was followed by the first stars and galaxies, which brought an end to the Dark Ages. These first luminous sources are thought to be the prime candidates which fuelled cosmic reionization, the last major phase transition of the Universe, from a neutral inter-galactic medium following recombination to the ionized state it remains in today. The physical processes which drive reionization encapsulate several areas of research, from cosmology and galaxy formation to radiative transfer and atomic physics. Even with the wealth of present-day observational information at our disposal, the processes are still not fully understood. Therefore we cannot model reionization analytically, instead turning to numerical simulations using observations to constrain our models. We perform a suite of fully-coupled radiation-hydrodynamical simulations of galaxy formation in cosmological volumes to probe the self-feedback of galaxies during the Epoch of Reionization. This research focuses on the transport of gas from the intergalactic medium onto dark matter halos, and consequences for semi-analytical models of galaxy formation. To improve on existing methods, which constrain the halo baryon fraction during reionization, we develop and train an artificial neural network to predict this quantity based on the physical properties of haloes. We demonstrate that this model is independent of redshift and reionization history, and can be trivially incorporated into semi-analytical models of galaxy formation. We further probe the physical processes which allow ionizing photons to escape from galaxies to reionize the Universe, specifically how stellar evolution uncertainties such as binary populations influence this process. Finally, we investigate to what extent a relative supersonic drift velocity between baryons and dark matter, present at recombination, may suppress the formation of the first objects and fundamentally alter their evolution. To do this, we develop a new method based on cosmological zoom simulations to include this effect in boxes much larger than the coherence length of the relative velocity for the first time.

Thesis (Ph.D.)--McMaster University (Canada), 1994. / Source: Dissertation Abstracts International, Volume: 56-08, Section: B, page: 4197. Adviser: D. M. Shaw.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Optical absorption line techniques have been applied to the study of a number of translucent molecular clouds in which the total column densities are large enough that substantial molecular abundances can be maintained. Results are presented for a survey of absorption lines of interstellar C2, CH, and CN. Detections of CN through the A2II -X2E+ (1,0) and (2,0) bands of the red system are reported, and are compared with observations of the blue system for one line of sight. The population distributions in C2 provide diagnostic information on temperature and density. The measured column densities of the three species can be used to test details of the theory of molecule formation in clouds where photo -processes still play a significant role. The C2 and CH column densities are strongly correlated with each other and probably also with the H2 column density. In contrast, the CN column densities are found to vary greatly from cloud to cloud. The observations are discussed with reference to detailed theoretical models.

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