Summary of the v_rad ESPRESSO measurements discussed in Sect. 8, in which the baseline is the average for each star for display purposes. The stars are shown with different colours and symbols: the black squares are for HE 0557−4840 with a mean velocity taken at 212.195 km s⁻¹; the violet stars are for HE 0233−0343 with (v_rad)_mean = 52.107 km s⁻¹; red downward triangles are for HE 1327−2326 with (v_rad)_mean = 63.681 km s⁻¹; the blue dots are for SMSS 0313−6708 with (v_rad)_mean = 298.560 km s⁻¹; and the green upward triangles are for SMSS 1605−1443 (v_rad)_mean = −226.173 km s⁻¹. Errors are 1σ. For reference, the black line crossing the panel is the average variation of HE 0107−5240 in the same interval.