AlF lines observed by ALMA towards o Ceti extracted from region 2 with a diameter of 0.168″ ~11R_⋆ (upper panel) and region 3 with diameter of 0.055″ × 0.07″ ~4 R_⋆ (lower panel) shown with black solid lines overlaid with model results (dashed lines). Models indicate that two separate rotational and vibrational temperatures are needed to reproduce all observed lines, which is discussed in Sect. 3.1. The line rest frequencies and transitions are marked in each panel. The grey dashed lines show the rms level. We note that the asymmetric feature in the right wing of the J = 10–9 line in region 3 might be due to a blend with a high excitation SO₂ line lying at 329.6459 GHz that becomes more prominent in the innermost regions of the circumstellar envelope.