Observed (blue) and model (red) ¹²CO lines towards R Scl (A = APEX, H = HIFI, I = IRAM, J = JCMT, S = SEST). The left panel corresponds to a 3 × 10⁵ cm^-3/10 K model, and the right panel to a 2 × 10³ cm^-3/100 K model. In both cases f_CO = 10^-3. The velocity scale is centred on the systemic velocity estimated to be –18.9 km s^-1. The dashed lines indicate the regions used in the fitting to the line intensities.