Starspots on WASP-107 and pulsations of WASP-118

Abstract

By analysing the K2 short-cadence photometry, we detect starspot occultation events in the light curve of WASP-107, the host star of a warm-Saturn exoplanet. WASP-107 also shows a rotational modulation with a period of 17.5 ± 1.4 d. Given that the rotational period is nearly three times the planet’s orbital period, one would expect in an aligned system to see starspot occultation events to recur every three transits. The absence of such occultation recurrences suggests a misaligned orbit unless the starspots’ lifetimes are shorter than the star’s rotational period. We also find stellar variability resembling ? Doradus pulsations in the light curve of WASP-118, which hosts an inflated hot Jupiter. The variability is multiperiodic with a variable semi-amplitude of ~200 ppm. In addition to these findings, we use the K2 data to refine the parameters of both systems and report non-detections of transit-timing variations, secondary eclipses and any additional transiting planets. We used the upper limits on the secondary-eclipse depths to estimate upper limits on the planetary geometric albedos of 0.7 for WASP-107b and 0.2 for WASP-118b.