Estimated filament parameters along the N(H₂) = 3 × 10²³ cm⁻² model filament, when the surface brightness includes 8 μm thermal dust emission. The filament is illuminated by an isotropic background (χ = 1) and a point source at Δy = 2.09 pc and a distance 0.94 pc to one side of the filament (cf. Fig. 14d). Red curves correspond to calculations with the true value of I^bg = 10 MJy sr⁻¹ and blue curves to a case where the median surface brightness from Fig. 14d is added to the estimate of I^bg. The black curves are for the case of a χ = 10 isotropic radiation field (no point source), with a similarly adjusted I^bg estimate.