Obliquities of Kepler Stars: Comparison of Single- and Multiple-Transit Systems

TL;DR

This study introduces a hierarchical Bayesian method to analyze stellar obliquities in Kepler systems, revealing that single-transit systems tend to have larger obliquities than multiple-transit systems, indicating more dynamically hot configurations.

Contribution

The paper develops a new Bayesian technique to infer obliquity distributions and applies it to Kepler data, uncovering differences between single- and multiple-transit systems.

Findings

Single-transit systems have larger stellar obliquities.

Multiple-transit systems are more orderly and flat.

Obliquity distributions differ significantly between the two groups.

Abstract

The stellar obliquity of a transiting planetary system can be constrained by combining measurements of the star's rotation period, radius, and projected rotational velocity. Here we present a hierarchical Bayesian technique for recovering the obliquity distribution of a population of transiting planetary systems, and apply it to a sample of 70 Kepler Objects of Interest. With ~95% confidence we find that the obliquities of stars with only a single detected transiting planet are systematically larger than those with multiple detected transiting planets. This suggests that a substantial fraction of Kepler's single-transiting systems represent dynamically hotter, less orderly systems than the "pancake-flat" multiple-transiting systems.