Left: Doppler-shadow measurements on MASCARA-4 b during transit as derived from observations taken with the CHIRON spectrograph on the SMARTS 1.5 m telescope. These consist of 60 mean stellar line profiles from which the average out-of-transit profile is subtracted, showing the movement of the dark planet in front of the fast-rotating star. The black horizontal lines denote t₂ and t₃ (dashed;the time when the orbiting object starts to ingress and egress) and t₁ and t₄ (solid; when the orbiting object starts to transit and is no longer transiting) of the transit. Observations started just after t₂. The dashed vertical black line represents the systemic velocity of the star, which is set to 0 km s⁻¹. The two vertical white dashed lines indicate the extent of the velocity broadened stellar line profile with a v sin i_* of 46.5 km s⁻¹. The white dotted line represents the best-fit model, corresponding to an impact parameter of , and |λ| of °. Right: visualisation of the orientation of the planet orbit with respect to the fast spinning star.