Sketch of the inner wind region of CW Leo indicating the different observations and results that signal a binary companion. From the modelling of the ALMA data, we infer an orbital axis with a PA of ~20° (Sect. 8.1). The reflex motion of the primary AGB star results in a one-armed spiral structure that is seen almost edge-on and with an extent almost reaching the orbital axis (full red arcs). The dust lane with a radius of ~0.5–1′′ situated in the orbital plane partly impedes the expansion of the spiral shock in the orbital plane direction (illustrated by the dashed red arcs).