Megan Shabram (Penn State)
Title: Hierarchical Bayesian Modeling for Exoplanet Populations from Kepler
Abstract: Using hierarchical Bayesian (HB) modeling, we explore the eccentricity distribution of a sample of short-period planet candidates using transit and occultation measurements from NASA's Kepler Mission. HB modeling is a technique growing in popularity in astronomy as it allows us to fully incorporate the measurement uncertainty into the inference of population level parameters. Additionally, with HB modeling we can attempt to account for biases that arrises in our sample of measurements. Understanding the eccentricity distribution for this subset of Kepler data is a step towards building a global characterization of the exoplanet population with long-term goals of linking planet and host star properties and probing planet formation mechanisms. Using hierarchical Bayesian (HB) modeling, we characterize the population parameters describing the underlying eccentricity distribution for both simulated and real planet populations. With a sample of ~ 50 planet candidates, we find that ~ 90% of planet candidates in our sample come from a population with an eccentricity distribution characterized by a small dispersion (most eccentricities are near zero), and ~ 10% come from a population with a larger dispersion (some planets in this population have larger eccentricities). We also investigate how the eccentricity distribution correlates with stellar effective temperature, planet radius, orbital period, and stellar metallicity. We find evidence that systems around higher metallicity stars and planet candidates with smaller radii are more dynamically complex, but caution that the significance of these results is limited by uncertainties in photometrically derived stellar metallicity and sample size. With HB modeling, we can tease out the existence of multiple populations in a sample, and look for correlations with these populations that provide clues about how planetary systems form. As time allows, I will describe recent progress investigating via HB modeling the mass-radius-ecentricity-TTV_amplitude relation for low-information-content TTVs. HB modeling can expose the mass-radius relation for this subset of planets by bypassing the mass-eccentricity degeneracy that arrises for low-information-content TTV systems.