Mass and optical depth values in selected RT models. The solid magenta line and the left axis show the estimated mass for the filament area, and the dashed magenta line and the right axis the corresponding mean optical depth τ(250 µm). The symbols show the J-band (triangles) and 250 µm (squares) optical depths (right axis) for the positions A (open symbols) and B (filled symbols). The red, black, and blue colours correspond to FWHM = 0.2, 0.5, and 0.9pc, respectively, and the small, medium, and large symbols to A_V = 0, 1, and 2mag. The x-axis is also labelled according to the FWHM and A_V values of the models.