¹²CO(2−1) line emission (merged data). (a) Doppler velocity spectra in different intervals of R as indicated in the insert. (b) V_z vs. R map integrated over position angles. The lines show thin spherical shells emitted 250 years ago with radial velocities of 10 and 7 km s⁻¹, respectively. (c) V_z vs. ω map integrated in the interval 0.2<R<2.5 arcsec. (d) V_z vs. ω map integrated in the interval 0.2<R<0.6 arcsec. The circle indicates the region covered by the red-shifted north-western octant discussed in Sect. 3.3.