Sample CCF profile during the night (panel a) and the residual (differential) CCF maps as a function of time (panels b–d). Panel b: illustrates the original residual CCF map after subtracting the mean out-of-transit CCF. The low-frequency modulations were subtracted based on the out-of-transit variations in panel c, in which the planet shadow is clearly seen. Panel d: residual map after the observed planet shadow is removed. The vertical dotted lines in panels a and c are the approximate CCF centre, representing the systemic RV of AU Mic. The near-vertical dashed linein panel d draws the maximum shift of the CCF bump by a spot-like feature on the stellar surface (≈ 3 km s⁻¹ over 0.25 day).