Transmission spectra of He I triplet and Hα and Na I doublet after GP correction. For each investigated line, the GP correction is shown. Left panel: transmission spectrum centred on the line (in the planet rest frame) with the GP regression model overplotted, along with the lσ uncertainty intervals (in blue), and the Gaussian+GP model (in red). Right panel: final transmission spectrum after removing the GP model. Vertical dotted black lines indicate the position of the investigated line. The error intervals for the Gaussian fit were computed by displaying 1000 Gaussian fits within the lσ uncertainties of the derived parameters, spanning the 16%–84% quantiles.