The Orbital Eccentricities of the Kepler M dwarf Planets: A PopulationLevel View of Planet Dynamics around Small Stars
Abstract
Exoplanet orbital eccentricities encode key information about planetary system formation and evolution. For M dwarf planets in particular, the proximity of the habitable zone to the host star makes eccentricity additionally important for understanding habitability. However, constraints on orbital eccentricity typically require long and resourceintensive radial velocity campaigns. We summarize an investigation to extract eccentricity measurements of 143 planets orbiting early to midM dwarfs across 81 systems, employing only their light curves from Kepler and host star density constraints from spectroscopy and Gaia. The "photoeccentric effect," described in exoplanet literature, enables the measurement of orbital eccentricity from a careful combination of transit duration and Kepler's 3rd law: both are linked to the stellar density. A disagreement between the stellar density inferred from the measured transit duration, and the density from Kepler's 3rd law, points to a nonzero orbital eccentricity. Employing our machinery in a standardized way on each of the 143 exoplanets, we derive an eccentricity posterior distribution for each. Through a hierarchical Bayesian analysis, we apply these individual posteriors to derive a populationlevel eccentricity distribution for planets around early to midM dwarfs. Comparisons between the eccentricity distribution for singly and multiplytransiting systems, as well as the distribution between M dwarfs and FGK dwarfs, help illuminate the dynamical states of M dwarf planets at a population level.
 Publication:

Bulletin of the American Astronomical Society
 Pub Date:
 June 2022
 Bibcode:
 2022BAAS...54e.380S