Population diagram for AlO. Circles and pentagons respresent detected lines, while triangles mark upper limits. The dashed blue line is the LTE linear fit to most of the detected lines (see text). The dotted magenta line is a fit to the two points with ϕ = 0.7. Black filled circles correspond to a non-LTE RADEX model with nearly the same parameters as constrained in the LTE fit and with H₂ density of 10⁹ cm^-3. Numbers in green show the visual phase corresponding to the datapoints.