Mapping a star with transits: orbit precession effects in the Kepler-13 system

TL;DR

This study analyzes Kepler-13b's transit data over 928 days to observe orbital precession effects, stellar activity, and surface features, revealing slow evolution in transit characteristics and potential stellar activity cycles.

Contribution

It provides detailed analysis of transit variations and stellar activity in the Kepler-13 system, highlighting the impact of orbit precession and stellar rotation on observed transit signals.

Findings

Transit duration, depth, and asymmetry evolve slowly over time.

Detected a significant clustering pattern linked to stellar rotation.

Identified potential stellar activity cycle around 300-360 days.

Abstract

Kepler-13b (KOI-13.01) is a most intriguing exoplanet system due to the rapid precession rate, exhibiting several exotic phenomena. We analyzed $Kepler$ Short Cadence data up to Quarter 14, with a total time-span of 928 days, to reveal changes in transit duration, depth, asymmetry, and identify the possible signals of stellar rotation and low-level activity. We investigated long-term variations of transit light curves, testing for duration, peak depth and asymmetry. We also performed cluster analysis on $Kepler$ quarters. We computed the autocorrelation function of the out-of-transit light variations. Transit duration, peak depth, and asymmetry evolve slowly, due to the slowly drifting transit path through the stellar disk. The detected transit shapes will map the stellar surface on the time scale of decades. We found a very significant clustering pattern with 3-orbit period. Its source is very probably the rotating stellar surface, in the 5:3 spin-orbit resonance reported in a previous study. The autocorrelation function of the out-of-transit light variations, filtered to 25.4 hours and harmonics, shows slow variations and a peak around 300--360 day period, which could be related to the activity cycle of the host star.