Van Hoof diagram for ρ Pup. The radial velocity curve associated to the Fe I  5410.91 (green) and Fe I  6393.60 Å (red) spectral line profiles is plotted as a function of the same quantity, but for Cr II  4634.07. The solid line corresponds to the identity function. There is no Van Hoof effect detected (no loops), while the γ-velocity effect is clearly seen (y-axis offsets of the curves).