Effects of spot occultations on exoplanet mid-transittiming measurements

It is critical to detect timing variations (TTV) in transit light curves in order to accurately determine the characteristics of transiting exoplanets. Due to disturbing effects in the system (if any, additional objects in the system, limb darkening, stellar activity, orbital precession, obliqueness of the host star), transit and mid-occultation times can change in the order of seconds, minutes, or hours, mostly sinusoidally. The effects of planetary occultation of surface spots observed in magnetically active host stars on the change in mid-transit times are investigated in this study.These effects were revealed using spot models and simulations of HAT-P-11, HAT-P-36, WASP-52 and other host star systems. Photometric data for HAT-P-11, HAT-P-36, and WASP-52 from UT50, T100, ETD, Kepler and TESS show that surface spots occulted by the planet during the transit event distort the light curves of these systems. We found that it affects mid-transit time measurements by 1 to 3 minutes. Furthermore, it has been calculated that the un-occulted spots that are not covered by being outside the transit chord affect the depth of transit, and that increasing the size of these un-occulted spots from 20 degrees to 40 degrees causes an 8% error in the planetary radius calculation. Keywords: spot occultation, stellar activity, planetary transit, transit timing variations