Glimpses of stellar surfaces. II. Origins of the photometric modulations and timing variations of KOI-1452

TL;DR

This paper introduces a unsharp masking method to analyze Kepler light curves, distinguishing star spot effects from gravitational influences in transit timing variations, and applies it to KOI-1452 to reveal stellar rotation and variability characteristics.

Contribution

The paper presents a novel application of unsharp masking to identify star spot effects in transit timing variations, especially in long cadence Kepler data, and demonstrates its effectiveness on KOI-1452.

Findings

KOI-1452's TTVs are non-gravitational in origin.

The primary star shows differential rotation periods.

The star likely exhibits g-mode oscillations, classifying it as a {b3}-Dor variable.

Abstract

The deviations of the mid-transit times of an exoplanet from a linear ephemeris are usually the result of gravitational interactions with other bodies in the system. However, these types of transit timing variations (TTV) can also be introduced by the influences of star spots on the shape of the transit profile. Here we use the method of unsharp masking to investigate the photometric light curves of planets with ambiguous TTV to compare the features in their O - C diagram with the occurrence and in-transit positions of spot-crossing events. This method seems to be particularly useful for the examination of transit light curves with only small numbers of in-transit data points, i.e., the long cadence light curves from Kepler satellite. As a proof of concept we apply this method to the light curve and the estimated eclipse timing variations of the eclipsing binary KOI-1452, for which we prove their non-gravitational nature. Furthermore, we use the method to study the rotation properties of the primary star of the system KOI-1452 and show that the spots responsible for the timing variations rotate with different periods than the most prominent periods of the system's light curve. We argue that the main contribution in the measured photometric variability of KOI-1452 originates in g-mode oscillations, which makes the primary star of the system a {\gamma}-Dor type variable candidate.