Velocity-integrated emission of less abundant isotopologues. We show, from left to right, ²⁹SiO J = 2−1, ³⁴SO N = 3−2, N = 2−1(2), and N = 2−1(3). The integration velocity range is 85-101 km s⁻¹ for ²⁹SiO, which is the range in which PN and ²⁹SiO are both detected. For ³⁴SO, we used: 81–105 for the N = 3−2 line, 88–104 km s⁻¹ for the N = 2−1(2) line, and 85.7–105.8 km s⁻¹ for the N = 2−1(3) line. The black contours start at the 3σ rms level of the integrated intensity maps, which is, from left to right, 1.6 × 10⁻² Jy beam⁻¹ km s⁻¹ ; 1.8 × 10⁻² Jy beam⁻¹ km s⁻¹ ; 1.7 × 10⁻² Jy beam⁻¹ km s⁻¹ ; and 8.7 × 10⁻³ Jy beairr¹ km s⁻¹, and the step is 10σ rms. The white contour corresponds to the 3σ rms level of the integrated map of PN, and the numbered regions 1 and 2 are those defined in Fig. 1. The synthesised beam is illustrated in the bottom-left corner.