Gravity darkening induced by rapid stellar rotation provides us with a unique opportunity to characterize the spin-orbit misalignment of a planetary system through analysis of its photometric transit. We use the gravity-darkened transit modeling code simuTrans to reproduce the transit light curve of Kepler-13Ab by separately analyzing phase-folded transits for 12 short-cadence Kepler quarters. We verify the temporal change in impact parameter indicative of spin-orbit precession identified by Szab\'o et al. (2012) and Masuda (2015), reporting a rate of change db/dt=(−4.1±0.2)×10−5 day−1. We further investigate the effect of light dilution on the fitted impact parameter and find that less than 1% of additional light is sufficient to explain the seasonal variation seen in the Kepler quarter data. We then extend our precession analysis to the phase curve data from which we report a rate of change db/dt=(−3.2±1.3)×10−5 day−1. This value is consistent with that of the transit data at a lower significance and provides the first evidence of spin-orbit precession based solely on the temporal variation of the secondary eclipse.
@article{arxiv.1711.02681,
title = {Spin-Orbit Misalignment and Precession in the Kepler-13Ab Planetary System},
author = {Miranda K. Herman and Ernst J. W. de Mooij and Chelsea X. Huang and Ray Jayawardhana},
journal= {arXiv preprint arXiv:1711.02681},
year = {2017}
}