Radial Velocity Observations and Light Curve Noise Modeling Confirm That Kepler-91b is a Giant Planet Orbiting a Giant Star

TL;DR

This study confirms Kepler-91b as a giant planet orbiting a red giant star by combining ground-based radial velocity data with Kepler observations and modeling stellar noise as a Gaussian Process.

Contribution

It provides the first unambiguous confirmation of Kepler-91b's planetary nature using combined data and advanced noise modeling techniques.

Findings

Kepler-91b is a 0.73+/-0.13 Mjup planet.

Stellar noise due to granulation affects data analysis.

Ground-based radial velocities confirm planetary status.

Abstract

Kepler-91b is a rare example of a transiting hot Jupiter around a red giant star, providing the possibility to study the formation and composition of hot Jupiters under different conditions compared to main-sequence stars. However, the planetary nature of Kepler-91b, which was confirmed using phase-curve variations by Lillo-Box et al., was recently called into question based on a re-analysis of Kepler data. We have obtained ground-based radial velocity observations from the Hobby-Eberly Telescope and unambiguously confirm the planetary nature of Kepler-91b by simultaneously modeling the Kepler and radial velocity data. The star exhibits temporally correlated noise due to stellar granulation which we model as a Gaussian Process. We hypothesize that it is this noise component that led previous studies to suspect Kepler-91b to be a false positive. Our work confirms the conclusions presented by Lillo-Box et al. that Kepler-91b is a 0.73+/-0.13 Mjup planet orbiting a red giant star.