Matching Items (8)
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- All Subjects: supernovae
- All Subjects: White Dwarfs
- Creators: Young, Patrick
- Member of: Theses and Dissertations
Description
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
Description
I combine, compare, and contrast the results from two different numerical techniques (grid vs. particle methods) studying multi-scale processes in galaxy and structure formation. I produce a method for recreating identical initial conditions for one method from those of the other, and explore methodologies necessary for making these two methods as consistent as possible. With this, I first study the impact of streaming velocities of baryons with respect to dark matter, present at the epoch of reionization, on the ability for small halos to accrete gas at high redshift. With the inclusion of this stream velocity, I find the central density profile of halos is reduced, overall gas condensation is delayed, and infer a delay in the inevitable creation of stars.
I then combine the two numerical methods to study starburst outflows as they interact with satellite halos. This process leads to shocks catalyzing the formation of molecular coolants that lead to bursts in star formation, a process that is better captured in grid methods. The resultant clumps of stars are removed from their initial dark matter halo, resemble precursors to modern-day globular clusters, and their formation may be observable with upcoming telescopes.
Finally, I perform two simulation suites, comparing each numerical method's ability to model the impact of energetic feedback from accreting black holes at the core of giant clusters. With these comparisons I show that black hole feedback can maintain a hot diffuse medium while limiting the amount of gas that can condense into the interstellar medium, reducing the central star formation by up to an order of magnitude.
I then combine the two numerical methods to study starburst outflows as they interact with satellite halos. This process leads to shocks catalyzing the formation of molecular coolants that lead to bursts in star formation, a process that is better captured in grid methods. The resultant clumps of stars are removed from their initial dark matter halo, resemble precursors to modern-day globular clusters, and their formation may be observable with upcoming telescopes.
Finally, I perform two simulation suites, comparing each numerical method's ability to model the impact of energetic feedback from accreting black holes at the core of giant clusters. With these comparisons I show that black hole feedback can maintain a hot diffuse medium while limiting the amount of gas that can condense into the interstellar medium, reducing the central star formation by up to an order of magnitude.
ContributorsRichardson, Mark Lawrence Albert (Author) / Scannapieco, Evan (Thesis advisor) / Rhoads, James (Committee member) / Scowen, Paul (Committee member) / Timmes, Frank (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2014
Description
Type Ia supernovae are important, but mysterious cosmological tools. Their standard brightnesses have enabled cosmologists to measure extreme distances and to discover dark energy. However, the nature of their progenitor mechanisms remains elusive, with many competing models offering only partial clues to their origins. Here, type Ia supernova delay times are explored using analytical models. Combined with a new observation technique, this model places new constraints on the characteristic time delay between the formation of stars and the first type Ia supernovae. This derived delay time (500 million years) implies low-mass companions for single degenerate progenitor scenarios. In the latter portions of this dissertation, two progenitor mechanisms are simulated in detail; white dwarf collisions and mergers. From the first of these simulations, it is evident that white dwarf collisions offer a viable and unique pathway to producing type Ia supernovae. Many of the combinations of masses simulated produce sufficient quantities of 56Ni (up to 0.51 solar masses) to masquerade as normal type Ia supernovae. Other combinations of masses produce 56Ni yields that span the entire range of supernova brightnesses, from the very dim and underluminous, with 0.14 solar masses, to the over-bright and superluminous, with up to 1.71 solar masses. The 56Ni yield in the collision simulations depends non-linearly on total system mass, mass ratio, and impact parameter. Using the same numerical tools as in the collisions examination, white dwarf mergers are studied in detail. Nearly all of the simulations produce merger remnants consisting of a cold, degenerate core surrounded by a hot accretion disk. The properties of these disks have strong implications for various viscosity treatments that have attempted to pin down the accretion times. Some mass combinations produce super-Chandrasekhar cores on shorter time scales than viscosity driven accretion. A handful of simulations also exhibit helium detonations on the surface of the primary that bear a resemblance to helium novae. Finally, some of the preliminary groundwork that has been laid for constructing a new numerical tool is discussed. This new tool advances the merger simulations further than any research group has done before, and has the potential to answer some of the lingering questions that the merger study has uncovered. The results of thermal diffusion tests using this tool have a remarkable correspondence to analytical predictions.
ContributorsRaskin, Cody (Author) / Scannapieco, Evan (Thesis advisor) / Rhoads, James (Committee member) / Young, Patrick (Committee member) / Mcnamara, Allen (Committee member) / Timmes, Francis (Committee member) / Arizona State University (Publisher)
Created2011
Description
Most stars form in groups, and these clusters are themselves nestled within larger associations and stellar complexes. It is not yet clear, however, whether stars cluster on preferred size scales within galaxies, or if stellar groupings have a continuous size distribution. I have developed two methods to select stellar groupings across a wide range of size-scales in order to assess trends in the size distribution and other basic properties of stellar groupings. The first method uses visual inspection of color-magnitude and color-color diagrams of clustered stars to assess whether the compact sources within the potential association are coeval, and thus likely to be born from the same parentmolecular cloud. This method was developed using the stellar associations in the M51/NGC 5195 interacting galaxy system. This process is highly effective at selecting single-aged stellar associations, but in order to assess properties of stellar clustering in a larger sample of nearby galaxies, an automated method for selecting stellar groupings is needed. I have developed an automated stellar grouping selection method that is sensitive to stellar clustering on all size scales. Using the Source Extractor software package on Gaussian-blurred images of NGC 4214, and the annular surface brightness to determine the characteristic size of each cluster/association, I eliminate much of the size and density biases intrinsic to other methods. This automated method was tested in the nearby dwarf irregular galaxy NGC 4214, and can detect stellar groupings with sizes ranging from compact clusters to stellar complexes. In future work, the automatic selection method developed in this dissertation will be used to identify stellar groupings in a set of nearby galaxies to determine if the size scales for stellar clustering are uniform in the nearby universe or if it is dependent on local galactic environment. Once the stellar clusters and associations have been identified and age-dated, this information can be used to deduce disruption times from the age distribution as a function of the position of the stellar grouping within the galaxy, the size of the cluster or association, and the morphological type of the galaxy. The implications of these results for galaxy formation and evolution are discussed.
ContributorsKaleida, Catherine (Author) / Scowen, Paul A. (Thesis advisor) / Windhorst, Rogier A. (Thesis advisor) / Jansen, Rolf A. (Committee member) / Timmes, Francis X. (Committee member) / Scannapieco, Evan (Committee member) / Arizona State University (Publisher)
Created2011
Description
Supernovae are vital to supplying necessary elements to forming bodies in our solar systems. This project studies the creation of a subset of these necessary elements, called short-lived radionuclides (SLRs). SLRs are isotopes with relatively short half-lives and can serve as heat sources for forming planetary bodies, and their traces can be used to date stellar events. Computational models of asymmetric supernovae provide opportunities to study the effect of explosion geometry on the SLR yields. We are most interested in the production of \iso{Al}{26}, \iso{Fe}{60}, and \iso{Ca}{41}, whose decayed products are found in our own solar system. To study the effect of explosion asymmetries in supernovae, we use TYCHO stellar evolution code, SNSHP smooth particle hydrodynamics code for 3D explosion simulations, Burn code for nucleosythesis post-processing, and Python code written to analyze the output of the post-processing code.
ContributorsJohnson, Charlotte (Author) / Young, Patrick (Thesis director) / Lunardini, Cecilia (Committee member) / Department of Physics (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
White Dwarf stars are the stellar remnants of low mass stars which have completed their evolution. Nearly all stars will become white dwarfs. The interior of a white dwarf encapsulates its evolution history: unraveling a white dwarf’s internal structure constrains the physical events which occurred to construct its composition. Variable, or pulsating, white dwarfs emit pulsations which are sensitive to their internal stratification. Just as seismology reveals Earth’s interior, asteroseismology can reveal stellar interiors. The standard approach to construe an observed white dwarf’s chemical makeup is to match observed pulsation properties to theoretical stellar models. Observed white dwarf pulsation data has reached 6-7 significant digits of precision. As such, it is important for computational modeling to consider systematic offsets from initial conditions and theoretical uncertainties that are within the detectable threshold. By analyzing the magnitude of pulsation differences among various uncertainties from white dwarf models, one can place constraints on important theoretical uncertainties. In this thesis, I explore impacts on white dwarf pulsations that result from accounting for various uncertainties in computational models. I start by showing the importance of 22Ne, and its impact on the pulsations in Helium atmosphere white dwarfs. Next, I discuss how certain trapped modes of white dwarfs may yield a signal for the 12C(α,γ)16O reaction rate probability distribution function. This reaction occurs during the Helium core burning phase in stellar evolution, and chiefly determines the Carbon and Oxygen abundance of white dwarfs. Following this work, I show how overshooting impacts the pulsation signatures of the 12C(α, γ)16O reaction rate. I then touch on the analytical work I’ve done regarding educational research in the HabWorlds course offered at Arizona State University (ASU). I then summarize my conclusions from these efforts.
ContributorsChidester, Morgan Taylor (Author) / Timmes, Francis X (Thesis advisor) / Young, Patrick (Committee member) / Li, Mingming (Committee member) / Borthakur, Sanchayeeta (Committee member) / Line, Michael (Committee member) / Arizona State University (Publisher)
Created2023
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 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
Description
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