Upper panel: part of chip 2 of the 2219.8 nm setting of 10 Leo, showing the pipeline-reduced stellar spectrum with telluric absorption (black line), and the telluric model made by Molecfit (red line). Lower panel: extract of the fully reduced 10 Leo spectrum, shown in the same wavelength region as the upper panel. Telluric lines have clearly been removed, and the spectrum has been further corrected as described in Sects. 3.3 and 3.4. Species from the Arcturus line list are marked, with the atomic identifications in purple and the molecular identifications in teal. Several of the atomic lines in this region, including the two prominent Na lines, are magnetically sensitive. Note the subtle tellurics blended with these Na lines. See Sect. 5 for further details.