4.2. Far Infrared Colours (PHT-C)

The FIR colour [C4-8] (Figures 1e, 2d, 3c) can distinguish all three geometries for all three types of stars for ₁₀₀ > 0.01. In addition, O4 can be easily distinguished from the other two star types. To identify between O7 and B0.5, the colour needs to be measured rather accurately (< 0.05 dex). The colour [C8-11] (Figures 1f, 2e, 3d) is very insensitive to the details of the models. If the colour is measured with better than 0.02 dex accuracy, then either the density distribution or the stellar type can be inferred.