Eclipse light curve of KELT-9b. Upper: raw light curve of HST/WFC3 for wavelengths of 1.12 − 1.27 μm for forward and reverse scanned data. We divide each orbit by the average of the two in-eclipse orbits. The result of this divide-in-eclipse method is shown in the middle panel in blue. Middle: eclipse light curve of HST/WFC3 split into three wavelength bins. The solid lines are best fits; the dotted line shows the stellar signal including pulsations, ellipsoidal variations, and Doppler boosting. The first orbit was discarded entirely. The inset shows the exposure affected by a satellite crossing. In our fits the grayed-out points in the first orbit, the points in egress, and the satellite crossing were excluded. Lower: residuals from the fit in the middle panel. The divide-in-eclipse method induces larger residuals outside eclipse, although a deviation from our model is still visible in egress. The RECTE equivalent of the lower two panels is shown in Appendix A.