Excitation temperature, T_ex, of the 44 GHz (upper panel) and of the 6₂−6₁-E 25.018 GHz line (lower panel) at different densities and for a temperature of 200 K. Curves are plotted until T_ex becomes positive. It is possible to convert ξ to methanol abundance using Eq. (3). We note that with increasing ξ, the excitation temperature typically transits from −infinity to +infinity before thermalising. The discrete nature of our grid in ξ occasionally obscures this fact.