Notes. The [C I] abundance profile is taken from Fig. 3 of Reach et al. (2022). A second model uses a constant abundance (with respect to hydrogen nuclei) of n(C0)/n(H) = 4 × 10⁻⁵ and r_in =4 × 10¹⁶ cm. We note that D is the distance to the source, r_in and r_out are the inner and outer radius of the shell, respectively, υ_exp is the expansion velocity, and Av is the line width (1/e half-width). The power-law indices for the fall-off of density and kinetic temperature (gas and dust temperature are assumed to be equal) with distance from the star are −2 and −0.50, respectively. For comparison, the temperature power-law index for purely adiabatic cooling at a constant expansion velocity would be −4/3 (Crosas & Menten 1997).