Schematic sketch presenting the proposed scenario. At the centre, the companion star is merging with the primary AGB star, within a common envelope. The cores of the two stars collide, and the kinetic energy is transferred to the fast-moving outflow, ejected along the polar direction. Shock fronts can be produced when the outflow hits the common envelope. On the orbital plane, the system is surrounded by a disc- or torus-shape structure, made of slow-moving material, some of which could also infall towards the system via the L2 point. The entire system is observed almost edge-on.