Exoplanet Weather: Reassessing Time Variability in Exoplanet Phase Curves

We reassess the claimed detection of variability in the atmosphere of the hot Jupiter HAT-P-7b, reported by Armstrong et al. (2016), using similar methods to look for time variation in the Kepler light curve of HAT-P-7. Using MCMC for phase curve fitting, we looked for statistically significant changes in the phase offset of HAT-P-7b’s phase curves over time. We identified apparently significant variations similar to those reported by Armstrong et al. (2016), and various tests confirmed the result to be mostly robust to different analysis strategies. However, when we injected non-varying phase curve signals into the light curves of similar stars and searched for variability using the same methods, we still found evidence for variability in those injected stationary phase curves. This suggests that un-modeled stellar or instrumental variability in the light curve may be contributing to the phase curve variation we measured for HAT-P-7b. Future studies seeking to detect time variability in photometric phase curves with telescopes like TESS should account for the impact of stellar variability on the measurements.