Massive search of spot- and facula-crossing events in 1598 exoplanetary transit lightcurves

Abstract

We developed a dedicated statistical test for a massive detection of spot- and facula-crossing anomalies in multiple exoplanetary transit lightcurves, based on the frequentist $p$-value thresholding. This test was used to augment our algorithmic pipeline for transit lightcurves analysis. It was applied to $1598$ amateur and professional transit observations of $26$ targets being monitored in the EXPANSION project. We detected $109$ statistically significant candidate events revealing a roughly $2:1$ asymmetry in favor of spots-crossings over faculae-crossings. Although some candidate anomalies likely appear non-physical and originate from systematic errors, such asymmetry between negative and positive events should indicate a physical difference between the frequency of star spots and faculae. Detected spot-crossing events also reveal positive correlation between their amplitude and width, possibly owed to spot size correlation. However, the frequency of all detectable crossing events appears just about a few per cent, so they cannot explain excessive transit timing noise observed for several targets.