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Starspots on WASP-107 and pulsations of WASP-118

Research paper by T. Močnik, C. Hellier, D. R. Anderson, B. J. M. Clark

Indexed on: 16 Feb '17Published on: 16 Feb '17Published in: arXiv - Astrophysics - Earth and Planetary Astrophysics



Abstract

By analysing the K2 short-cadence photometry we detect starspot occultation events in the lightcurve 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. The starspot occultation events do not seem to recur, which suggests a misaligned orbit unless the starspots' lifetimes are shorter than the star's rotational period. We also find stellar variability resembling gamma Doradus pulsations in the lightcurve of WASP-118, which hosts an inflated hot Jupiter. The variability is multi-periodic with a variable semi-amplitude of about 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.