ALMA and single-dish observations and the corresponding models (blue lines) for U Ant, based on the values presented in Table 3. The top left panel shows the spectrum of the ¹²CO (2 − 1) emission extracted from the ALMA data centred on the star, extracted from an aperture corresponding to ≈10% of the shell diameter. The telescope and CO transitions for the single-dish data are indicated in the respective panels. The shell expansion velocities are indicated with vertical dashed lines and are used as input for the shells in Fig. 1, right column.