Binned absorption spectrum (black dots) of HD 189733 b around lithium in the planetary rest frame, corrected using the local RVs (Sect. 4.3.2). The gray line shows the unbinned absorption spectrum and the red line the Gaussian fit on these data points. The blue horizontal dashed line indicates the white-light radius (R_p/R_★)² and the vertical one the position of the lithium line in the planet rest frame.