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3D models of white dwarf collisions are used to assess the likelihood of double-degenerate mergers as progenitors for Type Ia supernovae (henceforth SNIa) and to identify observational signatures of double-degenerate collisions. Observations of individual SNIa, SNIa rates in different galaxy types, and double white dwarf binary systems suggest that mergers

3D models of white dwarf collisions are used to assess the likelihood of double-degenerate mergers as progenitors for Type Ia supernovae (henceforth SNIa) and to identify observational signatures of double-degenerate collisions. Observations of individual SNIa, SNIa rates in different galaxy types, and double white dwarf binary systems suggest that mergers or collisions between two white dwarfs play a role in the overall SNIa population. Given the possibility of two progenitor systems (single-degenerate and double-degenerate), the sample of SNIa used in cosmological calcula- tions needs to be carefully examined. To improve calculations of cosmological parameters, the development of calibrated diagnostics for double-degenerate progenitor SNIa is essential. Head-on white dwarf collision simulations are used to provide an upper limit on the Ni-56 production in white dwarf collisions. In chapter II, I explore zero impact parameter collisions of white dwarfs using the Eulerian grid code FLASH. The initial 1D white dwarf profiles are created assuming hydrostatic equilibrium and a uniform composition of 50% C-12 and 50% O-16. The masses range from 0.64 to 0.81 solar masses and have an isothermal temperature of 10^7 K. I map these 1D models onto a 3D grid, where the dimensions of the grid are each eight times the white dwarf radius, and the dwarfs are initially placed four white dwarf radii apart (center to center). To provide insight into a larger range of physical possibilities, I also model non-zero impact parameter white dwarf collisions (Chapter III). Although head-on white dwarf collisions provide an upper limit on Ni-56 production, non-zero impact parameter collisions provide insight into a wider range of physical scenarios. The initial conditions (box size, initial separation, composition, and initial temperature) are identical to those used for the head-on collisions (Chapter II) for the same range of masses. For each mass pair- ing, collision simulations are carried out at impact parameters b=1 and b=2 (grazing). Finally, I will address future work to be performed (Chapter IV).
ContributorsHawley, Wendy Phyllis (Author) / Timmes, Frank (Thesis advisor) / Young, Patrick (Committee member) / Starrfield, Sumner (Committee member) / Fouch, Matt (Committee member) / Patience, Jennifer (Committee member) / Arizona State University (Publisher)
Created2012
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The first extrasolar planet discovered orbited the millisecond pulsar PSR B1257+12. These so-called "pulsar planets" have proved to be more uncommon than their early discovery might have suggested. The proximity of many known pulsar planets to their host neutron stars indicates that they formed post-supernova, possibly from material produced in

The first extrasolar planet discovered orbited the millisecond pulsar PSR B1257+12. These so-called "pulsar planets" have proved to be more uncommon than their early discovery might have suggested. The proximity of many known pulsar planets to their host neutron stars indicates that they formed post-supernova, possibly from material produced in the supernova. Any pre-existing planets that close would have been obliterated in the supernova. Material from the supernova falls back to an accretion disk around the neutron star analogous to a protoplanetary disk around a protostar. The composition of the supernova thus determines the composition of the planet-forming material. The pulsar planet then forms from collisions between particles within the disk. This research examines the composition of supernova remnants to explore this formation process. Chemical abundances of supernova ejecta were obtained from 3D supernova simulations. The velocities of particles containing silicate-mineral forming elements were filtered to determine what might stay in the system and thus be available for the formation of a fallback disk. The abundances of the remaining particles were compared to characterize the potential composition of such a fallback disk. Overall, the composition was roughly silicate-like, but the rates of mixing versus dust formation could lead to the production of highly exotic minerals.

ContributorsCranmer, Catherine (Author) / Young, Patrick (Thesis director) / Desch, Steven (Committee member) / Patience, Jennifer (Committee member) / Barrett, The Honors College (Contributor) / School of International Letters and Cultures (Contributor) / School of Earth and Space Exploration (Contributor)
Created2022-05