Close-up of the vortex in the α = 10⁻⁵ simulation at t = 692 binary orbits. Top-left: gas mid-plane density. The local overdensity and spiral arm pairs are clearly visible. Top-right: local vorticity. Strong anticyclonic regions are indicated in blue. Spiral arms are visible as red diagonal lines in the vicinity of the vortex. In both plots, black curves show contours of density. Middle: azimuthal density across the vortex centre. Bottom: radial density across the vortex centre.