Theses and dissertations

This collection includes both ASU Theses and Dissertations, submitted by graduate students, and the Barrett, Honors College theses submitted by undergraduate students. 

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Attempting to Produce Helium White Dwarfs From Low-Metallicity Solar Mass Stars

Description
I examine the effects of metallicity on solar mass stellar evolution, trying to replicate a previous result in Windhorst et.al., 2018, in which a zer metallicity solar mass star did not reach the AGB, and thus may turn into a helium white dwarf. In trying to replicate this result, I…

I examine the effects of metallicity on solar mass stellar evolution, trying to replicate a previous result in Windhorst et.al., 2018, in which a zer metallicity solar mass star did not reach the AGB, and thus may turn into a helium white dwarf. In trying to replicate this result, I used the M.E.S.A. stellar evolution code and was unable to reproduce this result. While M.E.S.A has undergone several updates since the previous result was obtained, more current evidence suggests that this may have been a one-time occurrence, as no helium white dwarfs were produced for low-metallicity models. Nonetheless, interesting results were obtained, including a lowest metallicity value for which CNO burning does not significantly contribute during the main sequence, 1 −10 Z , which produces noticeable effects on post main sequence evolution. All models are run with no rotation, one solar mass, and a series of MESA parameters kept constant, with the only exception being metallicity. Any metallicity value listed as Nd −10 is an absolute mass fraction, and Z is relative to solar metallicity, 2d*10 −2 .
ContributorsTompkins, Scott Andrew (Author) / Windhorst, Rogier (Thesis director) / Young, Patrick (Committee member) / School of Earth and Space Exploration (Contributor) / Department of Physics (Contributor) / Barrett, The Honors College (Contributor)
Created2019-12
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Population III Stars and Evolutionary Stellar Metallicity

Description
Study of the early Universe is filled with many unknowns, one of which is the nature of the very first generation of stars, otherwise designated as "Population III stars". The early Universe was composed almost entirely of cold hydrogen and helium, with only trace amounts of any heavier elements. As…

Study of the early Universe is filled with many unknowns, one of which is the nature of the very first generation of stars, otherwise designated as "Population III stars". The early Universe was composed almost entirely of cold hydrogen and helium, with only trace amounts of any heavier elements. As such, these stars would have compositions very different from the stars we are able to observe today, which would in turn change how these stars functioned, as well as their lifespans. Population III stars are so old that the light they emitted has not yet reached us here on Earth. Yet we know they have to have existed, so how do we go about studying objects that we have not yet observed? And more importantly, is there a metallicity threshold at which stars begin to behave like the stars we observe today? These areas are where stellar modelling programs such as TYCHO8 and the Spanish Virtual Observatory's Theoretical Spectra Web Server (TSWS) come in. These programs allow astronomers to model the physics of Pop III stars. We can get a pretty good understanding of how these stars behaved, how long they lived, and the visual spectra they would have emitted. Such information is crucial to astronomers being able to search for remnants of these stars, and one day, the stars themselves.
ContributorsMena, Julian (Author) / Young, Patrick (Thesis director) / Bowman, Judd (Committee member) / Barrett, The Honors College (Contributor) / School of Earth and Space Exploration (Contributor)
Created2022-05