Variations of the He i 5876 Å line. Upper panel: grey-scale representation. Bottom panel: the typical line profiles were selected from the spectra taken at SPM (R ~ 18 000). The vertical lines denote the central wavelength at laboratory frame (λ₀, sharp line) and at the frame connected with HD 50138. The line shift and its error bar are determined by the RV of the system rv_sys = 40 ± 4 km s^-1  based on the RVs of the [O i] λλ 6300, 6364 Å  lines.