Starspots on WASP-107 and pulsations of WASP-118

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. 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 γ Doradus pulsations in the lightcurve of WASP-118, which hosts an inflated hot Jupiter. The variability is multi-periodic with a variable semiamplitude 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.

Helium in the eroding atmosphere of an exoplanet

“…The highest peak in the periodogram and its full width at half-maximum corresponds to a periodicity of 19.7±0.9 days. This is consistent with estimates from Kelper light curves of 17.5±1.4 days 33 . We find an amplitude of ~0.00150 in magnitude.…”

“…Low-amplitude brightness variability is seen at a period of 8.675±0.043 days with a peak-to-peak amplitude of only 0.005 mag. Our period is almost exactly half the 17.5-day rotation period found in Kepler light curves 33 and demonstrates that WASP-107 has spots or spot groups on opposite hemispheres of the star during the epoch of our observations. The WASP-107b discovery team 6 also found periods of around 17 and 8.3 days in their 2009 and 2010 photometry.…”

“…Although WASP-107b orbits an active star we see no evidence of star spot crossings. For context, only five spot-crossing events are reported in 10 Kepler transits 16,33 .…”

WASP-104b is Darker Than Charcoal

“…We also performed the same analysis on the much-noisier publicly available long-cadence light curve reduced with the K2SFF procedure (Vanderburg & Johnson 2014) and somewhat noisier short-cadence light curve detrended with K2SC (Aigrain et al 2016), optimized for short-cadence data (Močnik et al 2017a). In both cases, we detect ellipsoidal modulation in agreement with our detection; however, we cannot confirm the Doppler and reflection modulations with these two light curves.…”

WASP-92, WASP-93, and WASP-118: transit timing variations and long-term stability of the systems

“…The ba-sic parameters of the parent stars are listed in the Table 1. Additionally we note that Močnik et al (2017) found γ Doradus pulsations in the light curve (LC) of WASP-118 with a period 1.9 day and semi-amplitude of ∼ 200 ppm. The aim of this paper was to study the possible presence of other planets in these systems.…”