K_p–Δυ_sys maps of the combined CO, H₂O and Fe detection in the atmosphere of MASCARA-1b for the pre-, post- and pre+post eclipse datasets. The atmospheric model used for the cross-correlation has combined contributions from the species and a thermal inversion as discussed in Sect. 3.1. The white dotted lines mark the detection peak, and the colour bar shows the detection significance computed from maps. The corresponding alpha detection significance and the conditional likelihood distribution of α are plotted in Fig. 4.