Planet Host Star Properties as Probes of Planet Formation and Evolution

Citation

Behmard, Aida (2023) Planet Host Star Properties as Probes of Planet Formation and Evolution. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/4mta-xt79. https://resolver.caltech.edu/CaltechTHESIS:05162023-173813482

Abstract

Over the past three decades, we have discovered over 5000 exoplanets that exhibit sizes, orbital architectures, and other properties that are often dramatically different from those of planets in our own Solar System. To understand the various processes that sculpted this diversity of planets, we can examine the stars they orbit. In the first project of my thesis, I modified a machine learning framework that models stellar spectra (The Cannon, Ness et al. 2015) to measure iron abundances for M dwarfs - small, cool stars that dominate the stellar population of our galaxy. Next, I combined Bayesian statistical methods and astrometric data that tracks the movements of stars to examine orbital alignment between planet host stars and their stellar companions. I discovered that close-in gas giant planet systems tend to be misaligned, which suggests that their dynamical histories include obliquity excitation through interactions with e.g., the protoplanetary disk and/or nearby stars. I then used Keck-HIRES spectroscopic observations and MESA stellar evolution models to uncover planet formation signatures encoded in host star elemental abundance patterns. I found that abundance differences between stars in binary systems may increase as a function of their separation, which has important implications for studies that rely on binary star chemistry. Most recently, I extended my abundance methodology to large spectroscopic samples to examine abundance patterns in planet host versus non-planet host stars, and thus explore planet formation signatures on a galactic scale.

Thesis Files