Observed (blue step line; with telluric correction) and the synthetic spectra before (orange) and after (green) their log 𝑔f values are calibrated (without the He 10 830) for star g1. Vertical dashed red lines indicate the position of the He 10 830 triplet, and the black arrows indicate the position of blending lines with log 𝑔f values calibrated (see Sect. 3). The spectra of the other eight target stars are plotted in grey as a reference.