Residual spectral series from nights 1 to 5. The y-axis represents the time or orbital phase. The residuals are binned to 0.006 in phase for clarity. The slanted dashed lines in red trace the expected planetary helium line. The dotted lines in blue denote the positions of the stellar He  I triplet. The shaded region in night 2 contains the telluric H₂O absorption and OH emission line, which overlap the expected planetary helium line.