Transmission spectrum of WASP-7 b around the Na i D₂ (left column) and Na i D₁ line (right column) by disregarding ten post-transit spectra. Top panels: Observed transmission spectrum (gray) along with best-fit model components, representing the CLV and RM effects (solid red). Middle panels: Observed transmission spectrum with the best-fit Gaussian absorption components (red), and with the model shown in the upper panels subtracted (gray). The gray shades denote 1σ uncertainty of the best-fit model (red). Bottom panel: Residuals with respect to the best-fit model. The black data points correspond to binning by a factor of 15.