Thesis (doctoral)--Stockholm University, 1998. / Includes bibliographical references.

Thesis--University of Wisconsin. / Issued in microfilm form in 1959. Includes bibliographical references.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 153-156).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1981. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 121-126).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [153]-173).

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, March 1999. / Includes bibliographical references. Also available on the Internet.

The 4.6m millimeter wave telescope at the University of British Columbia has been used to map a region 1/2° in diameter centered on 1=30°, b=0° in the J=1->0 transition of ¹²C¹⁶0. This study of the inner edge of the galactic molecular ring has revealed two well defined giant molecular clouds with diameters of approximately 30 pc and masses in the order of 5 x 10⁵ M⊙. In addition our analysis indicates that a substantial fraction, amounting to approximately 30%, of the integrated CO intensity comes from a feature covering the entire field observed. We have also found a complex of four clouds whose linewidths are a factor of two greater than those of the standard giant molecular clouds. The nature of these clouds is at present uncertain. The number of clouds detected in our survey gives as 5000 the total number of giant molecular clouds in the galaxy. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The cycle of star formation is the key to galaxy evolution. Stars form in massive collections of extremely dense cold gas. Stellar feedback will inject turbulence into the interstellar medium (ISM) and regulate the availability of more star-forming gas. This gas is an integral component in the cycle of star formation but is very difficult to model in numerical simulations. We have investigated the interplay between star formation and the structure of the ISM in numerical simulations. These simulations were done using the Smoothed Particle Hydrodynamics code Gasoline. For this work we introduce a new treatment for photoelectric heating in Gasoline. We first explore the impact of numerical parameter choices for the star formation threshold density, star formation efficiency and feedback efficiency. Of these three parameters, only the feedback efficiency plays a large role in determining the global star formation rate of the galaxy. Further, we explore the truncation of star formation in the outer regions of galactic discs and its relation to the presence of a two-phase thermal instability. In the outer regions of the simulated discs, gas exists almost exclusively in one warm phase, unsuitable to host large-scale star formation. We find that the disappearance of two-phase structure in the ISM corresponds to the truncation of star formation. / Thesis / Master of Science (MSc)

No description available.

Comets and Centaurs are icy remnants from the formation of the solar system. Analyzing the physical properties of their nuclei and their production rates can serve as powerful tools for tracing primitive solar system material. The four research projects in this dissertation examine these properties in comets and Centaurs. The first project focuses on observations of main belt comet 176P/LINEAR that were obtained with the Kepler space telescope. Optical lightcurves were used to constrain models of the nucleus's spin pole axis, shape and activity level. The second project used millimeter-wavelength spectra from the Arizona Radio Observatory Submillimeter Telescope and infrared photometry of Spitzer images to derive production rates of CO and CO2 from Oort Cloud comet C/2016 R2 (PANSTARRS). The third project is a compendium of CO, CO2, and H2O production rates in more than 25 comets and Centaurs that were obtained with a variety of space-based and ground-based telescopes and which were analyzed to test models of comet formation and evolution. CO, CO2, and H2O are the most abundant molecules observed in comets. The combination of these three molecules are likely the largest sources of elemental oxygen in the gas comae of comet and therefore a close approximation of the oxygen released in the comae. One key result of the survey is that CO/CO2 production rate ratios appear largely heliocentric dependent, with more CO produced the farther the comet is from the Sun. One exception is dynamically new comets which typically produce more CO2 than CO which is in predicted by models of significant cosmic-ray processing over time. The fourth project produced the first CO2 detection in a Centaur (39P/Oterma), which shows significant differences between the CO/CO2 in 39P and 29P, another Centaur, which may be partly due to different heating and processing histories.