Comparison of the PN N = 2–1 and SiO J = 2–1 line emissions. Left: high-velocity range. The PN N = 2–1 line flux (colourscale and red contours) is integrated in the velocity interval [−11;−5.3] km s⁻¹; the first contour and contour interval are 3σ (1.8 × 10⁻² Jy beam⁻¹ km s⁻¹) and 2σ (1.2 × 10⁻² Jy beam⁻¹ km s⁻¹), respectively. The SiO J = 2–1 emission (white contours) is integrated in the velocity interval [−19.7;−6.7] km s⁻¹; the first contour and contour interval are 20% and 15% of the SiO peak intensity, respectively. Right: low-velocity range. The PN N = 2–1 line flux is integrated in the velocity interval [−5.3;+4.6] km s⁻¹; the first contour and contour interval are 3σ (2.5 × 10⁻² Jy beam⁻¹ km s⁻¹) and 2σ (1.6 × 10⁻² Jy beam⁻¹ km s⁻¹), respectively. The SiO J = 2–1 emission is integrated in the velocity interval [−6.7; +3.7] km s⁻¹; the first contour and contour interval are 20% and 15% of the SiO peak intensity, respectively. The red and white ellipses depict the synthesised beams of the PN N = 2–1 and SiO J = 2–1 observations, respectively. Coordinates are in arcsecond offsets with respect to the nominal position of B1.