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Dwarf novae are a type of cataclysmic variable in which one of the components is a white dwarf. Their outbursts can range in brightness from two to five magnitudes at intervals that can vary from days to decades. The purpose of this study is to analyze the outburst of SS Cygni on the nights of June 18-22, 1987. Using an Interactive Reduction Software (IRS) package and a Gaussian fit program, the emission and absorption line strengths on the rise to outburst showed an increase in the flux as well as various other details supported by theory. / Dwarf novae -- Accretion disk -- SS Cygni -- Data analysis and results. / Department of Physics and Astronomy

The focus of this study is the change in accretion disk size in Dwarf Novae (DN), IP Peg. DN systems are a type of cataclysmic variable that experience periodic outbursts. These outbursts are caused by the release of gravitational potential energy from an increased rate of matter flow through the accretion disk. Throughout outburst, the radius of the accretion disk of the DN changes. Recent research done at Ball State University has suggested that the disk radius may not change as the disk instability model predicts. According to the disk instability model, the accretion disk should be at its largest radial size when the DN is at the peak of outburst. IP Peg in September and October of 2006 underwent outburst. It was found that during that particular outburst that the accretion disk was at its largest radial size on the decline from outburst and not peak. Further research into how the accretion disk changes with time is needed. / Department of Physics and Astronomy

Thesis (Ph. D.)--University of Wisconsin--Madison, 1949. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Bibliography: leaves 68-69.

Thesis (M.S.)--University of Wisconsin--Madison, 1961. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 33-36)

Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Bibliography: leaves 143-144.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Daniel T. Jaffe. Vita. Includes bibliographical references.

This dissertation explores the non-Doppler shifting of Helium lines in the high pressure conditions of a white dwarf photosphere. In particular, this dissertation seeks to mathematically quantify the shift in a way that is simple to reproduce and account for in future studies without requiring prior knowledge of the star’s bulk properties (mass, radius, temperature, etc.). Two main methods will be used in this analysis. First, the spectral line will be quantified with a continuous wavelet transformation, and the components will be used in a χ^2 minimizing linear regression to predict the shift. Second, the position of the lines will be calculated using a best-fit Levy-alpha line function. These techniques stand in contrast to traditional methods of quantifying the center of often broad spectral lines, which usually assume symmetry on the parts of the lines.

The number, height and age of western hemlock dwarf mistletoe (Arceuthobium tsugense (Rosendahl) G.N. Jones) infections were recorded in two western hemlock (Tsuga heterophylla (Raf.) Sarg.) stands (44 and 130 years old) located on similar sites on the University of British Columbia Research Forest at Maple Ridge, B.C.. The rapid decrease in numbers of infections with infection age was shown to be largely due to infection mortality. The rate of intensification of the disease expressed as "doubling time" was estimated to be 40 or more years in both stands. Also estimated was a rate of vertical spread of .15 metres per year. The results differed markedly from those of other studies in similar stands, which generally predict "doubling times" of 2 to 4 years and vertical spread rates of up to .5 metres per year. / Forestry, Faculty of / Graduate

As the remnants of stars with initial masses < 8 M⊙, white dwarfs contain valuable information regarding the formation histories of stellar populations. This dissertation focuses on using white dwarfs as tracers of Galactic evolution by first creating a self-consistent model of the Milky Way’s white dwarf population and comparing the results of various inputs to observational white dwarf catalogues. The model is applied to data from the Canada France Imaging Survey to derive the star formation histories of the thin disk, thick disk, and stellar halo. The results show that the Milky Way disk began forming stars (11.3 ± 0.5)Gyr ago, with a peak rate of (8.8 ± 1.4)M⊙ yr−1 at (9.8 ± 0.4)Gyr, before a slow decline to a constant rate until the present day — consistent with recent results suggesting a merging event with a satellite galaxy. Studying the residuals between the data and best-fit model shows evidence for a slight increase in star formation over the past 3 Gyr. The halo star formation history is relatively unconstrained owing to the relative rarity of halo white dwarfs. A complementary method to determine the age and star formation history is to obtain masses and temperatures to derive individual ages for a sample of halo objects. Using a sample of 18 spectra obtained at the Gemini Observatories the age of the inner halo is determined to be 9.3 ± 1.4 Gyr using the Cummings et al. (2018) IFMR and MIST isochrones, or 10.8 ± 0.6 Gyr using the relation from Kalirai (2012), however, the study determined that a bias is present in the mass determinations at low signal-to-noise and suggests that a larger, high signal-to-noise follow-up will be required to more accurately characterize this population. Finally, the future of white dwarf astronomy will be in good hands with the imminent start of the Legacy Survey for Space and Time (LSST) on the Vera C. Rubin Observatory, as well as several new space telescopes expected to begin operations later in this decade. The white dwarf population synthesis model is modified to simulate the WD populations in four upcoming wide-field surveys (i.e., LSST, Euclid, the Roman Space Telescope and CASTOR) and use the resulting samples to explore some representative WD science cases. The results confirm that LSST will provide a wealth of information for Galactic WDs, detecting more than 150 million WDs at the final depth of its stacked, 10-year survey. Within this sample, nearly 300,000 objects will have 5σ parallax measurements and nearly 7 million will have 5σ proper motion measurements. This sample will be used to detect the turn-off in the halo WD luminosity function for the first time, allowing for an accurate determination of the age and star formation history of the Milky Way at its earliest epoch. / Graduate