Doctor of Philosophy (PhD)
Physics and Astronomy
We have developed a framework for simulating binary stars through all three relevant
timescales: the dynamical merger, thermal, and nuclear evolution. The framework begins by simulating a dynamical merger in a 3-dimensional hydrodynamics adaptive mesh refinement code, Octo-Tiger, and performing a spherical averaging calculation to map the post-merger remnant into the 1-dimensional stellar evolution code, MESA. In this work, we primarily utilize this framework for simulating double white dwarf mergers, which are believed to be the progenitor to R Coronae Borealis (RCB) stars. We evolve the post-merger in MESA and compare the computed surface abundances to those observed in RCB stars. We also post-process these models with MPPNP for heavy metal nucleosynthesis. Although we are not able to perfectly match observations with this framework, we are able to perform a parameter study by "engineering" a post-merger to perfectly reproduce the surface abundances of an
RCB star. These models show that the large neutron density required for neutron capture reactions may actually be characteristic of the i-process rather than the s-process, which was thought to be active in RCB stars. We further extend the framework by simulating the merger of a giant and main sequence star, which is a possible progenitor for Betelgeuse. Although we are only able to reproduce the high rotation rate of Betelgeuse by suppressing angular momentum diffusion, we note that the extension of this framework represents a necessary step to perform holistic studies of mergers consisting of compact, main sequence and/or giant stars.
Munson, Bradley, "Stellar Binaries and Post-Merger Evolution: A Framework for Stellar Evolution and Nucleosynthesis in R Coronae Borealis Stars" (2023). LSU Doctoral Dissertations. 6063.