Removal of the Doppler shadow for the first night of data. Top panel: two-dimensional cross-correlation function as obtained when using a PHOENIX 10 000 K stellar atmosphere model template. The dark feature near − 40 km s⁻¹ is the Doppler shadow caused by the planet obscuring part of the disc-integrated stellar line, that is broadened by v sin i = 111.4 km s⁻¹ (Gaudi et al. 2017). The bright linear slanted feature is the signature of the atmosphere of the planet. It appears in this cross-correlation because the star and the planet have ionized lines in common (Hoeijmakers et al. 2018a). It is ignored when constructing and fitting the model of the Doppler shadow. Besides these, there are significant cross-correlation residuals due to stellar line-shape variations that we tentatively attribute to pulsations of KELT-9 that are not characterized in the literature as of yet, but seem to resemble those that have been observed in hot δ Scuti stars such as β Pictoris (Koen et al. 2003) and Wasp-33 (Collier Cameron et al. 2010). Middle panel: full model as fit to this cross-correlation function, where the dashed line indicates the polynomial fit to the centroid velocities of the main shadow feature in each exposure. Bottom panel: residuals after removal.