Comparison between the theoretical LTE (red) and NLTE (black) transmission spectra computed at a resolution of 100 000 in the UV and optical range (top) and in the near-infrared (bottom). Within each plot, the bottom panel shows the relative difference between LTE and NLTE (in percent). In the top panel, the blue horizontal dashed line indicates the location of the Roche radius in the planetary limb direction (i.e. perpendicular to the star-planet connecting line).