Characterization of Kepler-91b and the Investigation of a Potential Trojan Companion Using EXONEST

TL;DR

This study re-analyzed Kepler-91 data using Bayesian methods, confirming Kepler-91b's planetary nature and exploring a potential Trojan companion, but concluded the Trojan hypothesis is likely a false positive due to unphysical temperature predictions.

Contribution

It provides a detailed Bayesian re-analysis of Kepler-91b and investigates the possibility of a Trojan companion using multiple data sources and simulations.

Findings

Confirmed Kepler-91b as a planet

Favored the model with a Trojan companion but found it unphysical

Concluded the extra dimming is likely a false positive

Abstract

Presented here is an independent re-analysis of the Kepler light curve of Kepler-91 (KIC 8219268). Using the EXONEST software package, which provides both Bayesian parameter estimation and Bayesian model testing, we were able to re-confirm the planetary nature of Kepler-91b. In addition to the primary and secondary eclipses of Kepler-91b, a third dimming event appears to occur approximately $60^o$ away (in phase) from the secondary eclipse, leading to the hypothesis that a Trojan planet may be located at the L4 or L5 Lagrange points. Here, we present a comprehensive investigation of four possibilities to explain the observed dimming event using all available photometric data from the Kepler Space Telescope, recently obtained radial velocity measurements, and N-body simulations. We find that the photometric model describing Kepler-91b and a Trojan planet is highly favored over the model involving Kepler-91b alone. However, it predicts an unphysically high temperature for the Trojan companion, leading to the conclusion that the extra dimming event is likely a false-postive.