Date of Award

Fall 11-21-2025

Document Type

Dissertation

Degree Name

Ph.D. in Physics and Astronomy

Organizational Unit

College of Natural Science and Mathematics, Physics and Astronomy

First Advisor

Jennifer L. Hoffman

Second Advisor

Shannon Murphy

Third Advisor

Toshiya Ueta

Fourth Advisor

Tristan Weber

Fifth Advisor

William Raph Hix

Copyright Statement / License for Reuse

All Rights Reserved
All Rights Reserved.

Keywords

Core-collapse supernovae, Hydrodynamics, Observations, Spectropolarimetry, Supernovae

Abstract

Supernovae (SNe) are the energetic deaths of massive stars, dispersing heavy elements throughout the galaxies and shaping cosmic evolution across the universe. However, understanding the connections between the evolution of massive stars, their catastrophic demises, and the myriad of observed SNe, remains a fundamental challenge in astrophysics. My work aims to narrow this gap by integrating extensive observational data with advanced hydrodynamical simulations to better interpret SNe observations and understand the origin of their geometry. The observational component utilizes the largest spectropolarimetry dataset of stripped-envelope (SE) core-collapse supernovae (CCSNe) gathered by the SNSPOL project. Analyzing nine Type Ib and eleven Type Ic SNe across multiple epochs, I identify common features across the sample that I then use to infer ejecta structures and element distributions, providing insight on the pre-explosion mixing process. To complement the observational component, I use a combination of state-of-the-art hydrodynamical models to simulate SNe arising from 14- and 26-solar mass stripped envelope (SE) progenitors. To improve current model setup, I engineered a new density formula for a more realistic distribution of circumstellar material (CSM) using mass-loss data from each type of progenitor star. I then propagated each explosion into this CSM, as well as a less dense CSM configuration, and modeled the SNe out to 7+ days post bounce, which allowed me to compare the simulated ejecta back to my observational sample.

From the observational data I find that SNe Type Ib and Ic exhibit an average continuum polarization level of P = 0.85 ± 0.06 and P = 1.18 ± 0.08, respectively. This level of polarization is consistent with elongated photospheres, which deviate from spherical symmetry at the level of 20 − 30%. Additionally, for all SNe in my sample I also measure line polarization magnitudes above the continuum level, for one or more of the Fe II, He I, Ca II and O I], line regions. Several of these polarized line regions also exhibit loops or linear trends in the q−u plane, indicative of that material being distributed in more complex asymmetric structures such as clumps, polar caps, or disks. The results of my hydrodynamical SN models show that both the largescale geometry of the ejecta and distribution of elements is highly dependent on the CSM configuration with which the SN interacts. Models with the more realistic CSM result in more asymmetric ejecta and higher levels of mixing compared to models with the less dense CSM, in which the SN maintains the structure produced during shock breakout. Doing a rough calculation to isolate excited material at visible opacities I also find potential signatures of helium and iron clumps in the more realistic CSM models. Together my results provide a path to disentangle observational signatures which may be inherent in the explosion process from those produced during CSM interaction. As a next step, I suggest the results of my models be applied as input parameters for radiative transfer models able to simulate photon absorption and emission processes from scattering interactions.

JEL— C45, C51, C52

Copyright Date

11-2025

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Rights Holder

Jennifer L. Hoffman

Provenance

Received from ProQuest

File Format

application/pdf

Language

English (eng)

Extent

277 pgs

File Size

123 MB

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