Optical secondary eclipse observations of WASP-12b

Detecting and measuring thermal emission from exoplanets immediately before and after occultation by their host stars is an important tool for studying exoplanet atmospheres. To date, secondary eclipse observations have largely been at wavelengths red-ward of 1 μm, in no small part due to the fact that most targets are insufficiently large or hot to have detectable secondary eclipse signals at shorter wavelengths with current instrumentation. Observations of secondary eclipses in the i- and z-bands are of particular interest as this window contains prominent TiO and VO features (compounds thought to give rise to temperature inversions in the hottest exoplanets) and are good discriminators between models for carbon-rich and carbon-poor planets. However, numerous seemingly high-precision detections of z-band secondary eclipses have reported significantly different depths—most notably in the cases of WASP-12b and WASP-19b. Whilst these discrepancies could be indicative of the challenges associated with measuring the small thermal emission signals at these wavelengths, another possible explanation is the variability of the thermal emission properties of the planet itself due to storms. Weight has been added to the storm hypothesis by observed variations in offsets in the peak of HAT-P-7b’s phase curve at optical wavelengths. I will present three i-band secondary eclipse observations of WASP-12b taken taken over the course of a year with INT/WFC and LT/IO:O, where preliminary analysis shows variations in the eclipse depths between the three nights.

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