Clouds on Ultra Hot Jupiters and eclipse variability

The atmospheres of transiting planets can be studied and analysed through primary transits, secondary eclipses and the phase curve modulation. With the secondary eclipse technique, one can study the emission of the full day-side and the thermal structure of the planet. One may expect a change in the secondary eclipse depth, symptomatic of a variation of the albedo due to the presence of clouds on their hot sides.

We analysed the secondary eclipse variability from orbit to orbit of four Ultra Hot Jupiters : WASP-18b, KELT-9b, KELT-1b and WASP-121b. They belong to a class of tidally locked giant gaseous exoplanets with short orbital period, small semi-major axis and very high equilibrium temperature (greater than 2000K). Each eclipses and transits were fit with a Mandel & Agol Model analysed with an MCMC and STEPPAR procedure.

Unfortunately, the level of scatter found in secondary eclipse depth was similar to the one found in transit depth which cannot be attributed only by the presence of clouds.