Transits of KELT-9 b observed with CHEOPS. The x-axis shows the orbital phase, with the y-axis showing the normalised flux from the star. There is an offset of 0.007 in terms of normalised flux between the individual transits. The black dots represent the data, which were corrected for the roll angle of the satellite using PYCHEOPS and were fitted with TLCM, leading to the transit models (red lines). The lowest transit resulted from the single transit observation listed in Table 1; the rest were observed in phase curves (Jones et al. 2022).