UCLA

Planetary orbital eccentricities are key to probing the formation and evolution pathways of exoplanets. Eccentricity measurements can be made through a variety of observing techniques that currently tend to be limited by signal-to-noise constraints, data quality limitations, or model biases, often leading to poorly constrained eccentricities for sub-Jovian-size planets. To better understand the typical and extreme values of planetary eccentricities for planets of all sizes, I investigated the photometric eccentricities of TESS planets and accurately constrained the eccentricity distributions of both individual planets and planet sub-populations. I used existing methods to identify several high-eccentricity sub-Jovian-size planets from TESS transit photometry and confirmed their eccentricities via follow-up radial velocity measurements (Chapters 2 and 3). Through these discoveries, I identified an unaccounted-for bias in a common transit modeling method which unfairly skewed photometric eccentricity constraints towards higher values. I worked with a small team of collaborators to mitigate this bias and proposed an alternative transit model parameterization that yields accurate transit fits and unbiased eccentricity constraints (Chapters 4 and 5).

I used our proposed modeling approach to homogeneously measure the transit properties of 108 planets from the TESS-Keck Survey (TKS), including constraints on orbital periods, transit-timing variations, and planet-to-star radius ratios (Chapter 6). In addition to measuring these transit properties, I also performed precise stellar characterization that allowed me to measure planet radii and constrain orbital eccentricities via importance sampling with stellar density. These homogeneously-constrained posterior distributions of eccentricity from my photometric modeling served as the foundation for my hierarchical Bayesian analysis of the population-level eccentricity distribution of the TKS planet sample -- a first among TESS planets (Chapter 7). Through this analysis, I found that sub-Jovian-size planets display a lower underlying eccentricity distribution than Jovian-size planets -- the first confirmation of this trend shown via hierarchical Bayesian modeling. I found a similar distinction between the eccentricities of planets in single-planet systems versus multi-planet systems, with the latter displaying lower eccentricities. I also demonstrated that the results of such hierarchical analyses can be used to improve the individual measurement precisions of planet radii, impact parameters, and eccentricities. The parameter constraints and dynamical trends revealed through this hierarchical analysis of exoplanet eccentricities will help improve our understanding of the dynamical processes that drive the evolution of observed planetary systems.