Comparisson between observed and synthetic NaCl velocity-channel maps.Top: ALMA velocity-channel maps of the NaCl(υ = 0, J = 20–19) transition; in the last panel, we show the continuum ALMA maps obtained using the line-free channels of the spectral window that covers that transition. All maps are rotated by 25° clockwise so the symmetry axis of the disk is vertical. Contours in the line and continuum maps are spaced every 1.1 mJy/beam, equivalent to 50 K in main-beam temperature units. The clean beam (HPBW=0″.02 × 0″.02) is plotted at the bottom-left corner of each panel. The dashed ellipse represents the dust disk model deduced from the analysis of the continuum maps presented in § 3.1 and Fig. 1. The position of QXPup, coincident with the continuum emission peak, is indicated by the purple star-like symbol. Bottom: Synthetic NaCl (υ = 0, J = 20–19) velocity-channel maps from our model (§ 5.2), represented as in the top panel.