Tori Bonidie Dissertation Defense

Thesis Title: Probing Ultra-Hot Jupiter Atmospheres with High-Resolution Spectroscopy: An Exploration of Dayside Chemistry and Thermal Structure Abstract: Characterizing exoplanet atmospheres is essential to understanding the formation pathways and evolutionary processes underlying the diversity of planetary systems we observe today. Although space-based observations have dominated atmospheric characterization, advancements in both instrumentation and data processing techniques have enabled ground-based high-resolution spectroscopy (HRS) to emerge as a powerful tool for probing exoplanetary atmospheres. HRS has the capability to resolve individual exoplanetary spectral lines and detect species present in the atmosphere through cross-correlation, while newly emerging cross-correlation-to-log-likelihood (CC-to-log L) mapping techniques allow for quantitative constraints on the chemistry and thermal structure of gas giant exoplanets. In this thesis, I develop a Bayesian retrieval framework built on CC-to-log L mapping and apply it to emission spectroscopy of the ultra-hot Jupiter (UHJ) KELT-20 b, constraining its chemical composition and pressure-temperature profile and deriving separate dayside and nightside terminator constraints that reveal differences in chemistry and temperature as a function of planetary longitude. Building on this foundation, I introduce further advancements to the retrieval framework that allow for greater flexibility in chemical and pressure-temperature parameterizations, and apply this approach to an emission spectroscopic survey of four UHJs, whose initial results reveal trends in atmospheric chemistry across the sample, including evidence for atmospheric nickel enrichment and a temperature-dependent depletion of calcium and titanium. Finally, I discuss the implications of these findings for the physical and chemical processes that shape ultra-hot Jupiter atmospheres, along with the continuing role of HRS in advancing our understanding of e