The Interplay of Waves and Stellar Evolution

Citation

Wu, Samantha Chloe (2024) The Interplay of Waves and Stellar Evolution. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/kmc6-kn66. https://resolver.caltech.edu/CaltechTHESIS:05202024-175837810

Abstract

In this thesis, I study the evolution of stellar interiors and stellar oscillations in order to address current observational puzzles in astronomy. The thesis focuses on refining physical models for pre-supernova outbursts from massive stars, tidal evolution of planetary architectures, and progenitors of compact neutron star binaries. In order to research these topics, I combine calculations of internal stellar oscillation modes with stellar evolution models, to account for the evolution of the modes across the stars' lives. I begin by introducing some concepts in stellar evolution and internal stellar oscillations which underlie the physical intuition and models present throughout the thesis.

In the second chapter of the thesis, I present a study of tidal dissipation in M-dwarfs hosting nearby exoplanets. I model dynamical tides from normal modes of stellar oscillation across stellar evolution. With my novel methods, I am able to resolve the detailed spectrum of tidal dissipation as a function of stellar age. This empowers our evolutionary calculations to capture the resonance locking phenomenon, in which sustained tidal excitation of modes to large amplitudes over long intervals of stellar evolution produces enhanced dissipation. I find that Earth-mass and Jupiter-mass planets around M-dwarfs experience significant orbital migration under the influence of resonance locking with inertial modes of the star.

In the third and fourth chapters of the thesis, I explore the ability of waves generated by vigorous core convection in massive stars to impart heat to the stellar envelopes. I model the excitation and propagation of waves during phases of energetic nuclear burning in stars to assess the amount of energy that waves transmit to the envelope, as well as the timescale before core collapse when the majority of wave heating occurs. I find that wave heating is unlikely to independently produce very massive circumstellar material (CSM), but induces large expansion that could trigger interaction with a binary companion and thereby drive the intense mass loss that is expected to precede interacting supernovae.

The fifth chapter explores this very mechanism of binary interaction to produce pre-supernova outbursts. Even without wave heating, stripped stars can expand greatly in the years before core collapse simply as a consequence of stellar evolution. I employ binary stellar evolution simulations to study how stripped stars of around 2-3 solar masses interact with neutron star companions, crucially focusing on the often-omitted stages from oxygen/neon (O/Ne) burning onward. I observe the stripped stars to undergo extremely high rates of mass loss, which can form a distribution of dense CSM around the system. My estimates for the CSM mass and radius are consistent with observed low ejecta-mass, interacting supernovae.

Thesis Files