Planet-moon model fit to the CHEOPS light curve of v² Lup. Top panel: PIPE-subarray light curve (blue points with error bars) modelled with a combination of instrumental effects (blue curve), stellar noise (green curve) and transits of a planet and moon. The model including all these effects is shown in orange. The shaded grey region shows the physically plausible moon mid-transit times within the planet’s Hill sphere. Middle panel: Light curve corrected for the instrumental and stellar noise models (blue points), together with the best-fit planet-moon transit model (orange curve). The dashed black curve shows the isolated moon component. Bottom panels: Residuals from the planet-model fit and planet-only fit. The open black circles show the light curve binned into 20-minute intervals. As described in Sect. C, the shallow transit feature clearly appearing in the second panel from top is an artefact.