The orbital eccentricity distribution of planets orbiting M dwarfs

Area of Science:

• Exoplanetary Science
• Stellar Astrophysics
• Planetary Dynamics

Background:

• M dwarf stars are the most common stellar type in the Milky Way.
• Understanding exoplanet orbital characteristics around M dwarfs is crucial for comparative planetology.
• Previous studies on FGK stars provide a basis for comparison with M dwarf systems.

Purpose of the Study:

• To investigate the underlying distribution of orbital eccentricities for planets orbiting early-to-mid M dwarf stars.
• To determine if distinct subpopulations of planets exist based on their orbital characteristics.
• To compare exoplanet eccentricity distributions between M dwarf and FGK star systems.

Main Methods:

• Analyzed a sample of 163 planets in 101 systems detected by NASA's Kepler Mission.
• Constrained orbital eccentricity using Kepler lightcurves and stellar density priors (metallicity, K magnitude, Gaia parallax).
• Applied a Bayesian hierarchical framework to extract eccentricity distributions, testing Rayleigh, half-Gaussian, and Beta functions.

Main Results:

• The eccentricity distribution for apparently single-transiting planets is best described by a Rayleigh distribution (σ = 0.26).
• Multitransit systems exhibit a distinct, narrower eccentricity distribution (σ = 0.12).
• Single-transit data favor a mixture model of two Rayleigh distributions (σ = 0.18 and σ = 0.43), suggesting dynamically distinct subpopulations.

Conclusions:

• The findings suggest the presence of dynamically 'warm' and 'cool' exoplanet subpopulations around early-to-mid M dwarfs.
• This contrasts with the generally cooler eccentricities observed in multitransit systems.
• The derived eccentricity distribution refines our understanding of planet formation and evolution around the most common stars in the galaxy.