Excess absorption of metastable helium in the stellar frame. The degree of day-night anisotropy is increasing from left to right. The horizontal lines indicate the extent of the optical transit, while the tilted lines show the Doppler-shifted wavelengths of the helium triplet in the planetary rest frame. The vertical brown lines correspond to the stellar rest frame. The red cross indicates the wavelength of the mid-transit maximum absorption; the deviation from the vacuum wavelength is converted to a shift velocity. With an increasing day-night anisotropy, the line profiles become blueshifted and narrower. There is only minor excess absorption before and after the ingress and egress phases.