Variability of KELT-1b’s dayside as seen by CHEOPS and TESS

Taking advantage of CHEOPS' precision and flexible pointing strategy, we explored the variability of the atmosphere of KELT-1b. KELT-1b is a transiting brown dwarf (MP= 27MJ)  orbiting very close to its host star (P=1.2 days), its orbit and high irradiation make it similar to an ultra-hot Jupiter. We combined occultation observations over 29 epochs with CHEOPS and three TESS sectors, together spanning over five years. We manage to obtain precise measurements of the brown dwarf's occultation depths over time. The individual occultations observed by CHEOPS reveal hints of atmospheric variability. In the TESS data, we also find a significant variation (>4  sifma) among the sectors. These results suggest time variability in the dayside of KELT-1b's atmosphere, potentially caused by a variability in cloud coverage."