Power-law radial distribution of the gas kinetic temperature estimated from non-LTE excitation and radiative transfer models of the CO emission in a number of AGB envelopes (indicated at the top of the box using the same colour for the temperature laws) from the literature. References: Van de Sande et al. (2018); Maercker et al. (2016); Khouri et al. (2014); Decin et al. (2010). The solid and dotted lines of R Dor and IK Tau are different temperature profiles derived by different authors (solid from Maercker et al. 2016, and dotted from Van de Sande et al. 2018 – R Dor and Decin et al. 2010 – IK Tau). The thick black line is an average temperature law.