Left panel: astrometric measurements of the relative position of δ Vel B (crosses) with respect to δ Vel A ( ⋆  symbol), with our best-fit orbital solution (solid ellipse, see Table 6 for the orbital parameters). Thin lines connect each measurement to the corresponding point on the adjusted orbit. The dotted line corresponds to the periastron passage, and the diamonds correspond to the position of δ Vel B on January 1 every ten years between 1890 and 2020. Right panels (labeled 1 to 4): correspond to zooming boxes on the larger view. NACO and VISIR data (panel 1) are tabulated in Table 5; the data in panel 2 come from Horch et al. (2000); the data in panel 4 are from Tango et al. (1979). Zooming boxes’ positions are reported on the main (left) panel.