Line-of-sight velocities (bottom large panels) as defined in Eq. (10), applied to HD 142527 with i = 27 °, and varying PA. Top panels: exhibit the corresponding polar components. Color reflects implied Doppler-shifts in molecular lines. Blue/orange dots indicate extreme values in . Leftmost panel: vortex’s spatial extension is shown as a solid contour which corresponds to Σ = 0.5Σ₀, where Σ₀ is the scaling factor used in Eq. (3). The inner cavity, where fast spiral waves are launched but surface density is low, is not shown here : regions with Σ∕Σ₀ < 0.1 are masked. As a proxy for the vortex’s eye, a black cross indicates the density maximum.