Position-velocity diagram in the direction from PA = 45° to 225° obtained from the continuum-subtracted channel maps of the ³⁰SiO line (v = 1, J = 6–5). The pink, red, and light blue curves at the negative spatial offsets (on the side of PA = 45°) represent the traces expected from shells infalling at velocities of 2 km s⁻¹ at a radius of 75 mas, 7 km s⁻¹ at 50 mas, and 13 km s⁻¹ at 42 mas, respectively. The blue curve on the PA = 225° side shows the trace from an infalling or outflowing (although infalling is more plausible) shell with a velocity of 12 km s⁻¹ at a radius of 45 mas. See Sect. 4.4.