I am a senior undergraduate studying physics at Illinois State University, seeking graduate programs for fall 2023. I have participated in a number of computational research projects, most of which exploring diffusion in white dwarfs. Over the summer of 2022, I have worked closely with Dr. Daniel Lecoanet on connecting magnetic fields to gravity mode oscillation. At Illinois State, I am a section leader of the marching band, a member of the ISU Physics club, and an avid rock climber. In my spare time I enjoy playing/learning new instruments, exploring weird rabbit holes, and playing board games with friends.
Stars wiggle. We can observe those wiggles. Gravity waves (not gravitational waves, these are buoyancy oscillations) can be observed with time series. G modes tell us about the internal structure of stars, and have recently allowed us to detect near-core magnetic fields. At the interface between the stably stratified outer-core regions and convective cores of these massive stars (slowly pulsating B type and Gamma-Doradus stars), an strong interaction between gravity waves and the near-core radial magnetic field occurs. Using computational data, we are able to produce a connection between theory and observation to detect near-core magnetic fields of these stars.
Magnetic fields near the surfaces of massive stars have been observed in the past, but only one observation of near-core magnetic fields has been successfully completed. Magnetic fields are important for stellar formation and evolution. Near-core observations/detections are essential in cohesively understanding and simulating these phenomena. By solving a modified magnetohydrodynamical equation, we can calculate the precise interaction with the magnetic field and gravity waves using the open-source Python package Dedalus. Using these data, we can produce a clear and accurate map of observed frequencies to near-core magnetic field strength.
White dwarf stars are largely made up of Carbon-12 and Oxygen-16, but there are trace amounts of high-charge, neutron rich elements like Neon-22, Iron-56, and even Uranium-235 and 238. Stellar evolution heavily depends on the chemical composition and diffusion of these trace heavy elements. Previous models of diffusion work well at low and high temperatures, but until 2021, there was no cohesive law that combined the low-coupling (hot) and cold regimes. By combining the Chapman-Spitzer law of diffusion, and an Eyring diffusion model, we were able to effectively reduce the error of previous diffusion laws by around 10%, but our diffusion law only applied to one-component plasmas.
While we reduced the absolute error by a significant amount, our model was only accurate for one-component plasmas. With some heavy emphasis on theory, we found a generalization of the OCP case to produce one single law that encapsulated most of the temperature and charge ranges that are important for white dwarf astrophysics. This generalization can be utilized in stellar evolution codes like MESA, especially since the single analytical equation replaces what used to be a piece-wise function over the improtant regimes.
As white dwarfs cool, their cores crystallize. White dwarfs have trace amounts of heavy elements. Do these crystallize as well? It has been shown that Neon-22 crystallizes in approximately the same temperature and coupling regimes as the carbon and oxygen background. We showed that Iron-56 behaves in a similar way, but iron will precipitate and sediment toward the core before the rest of the star crystallizes. Following this process, the star becomes more tightly bound, and energy is released from the sedimetnation process. The full effects these processes have on white dwarf evolution is still unknown and needs further exploration.