Results of the SED fitting using the reference dust described in the text (Sect. 4). Left: confidence limits on dust opacity index β and gas emission index α_ff; contours represent the 68% and 95% confidence levels for the fit (i.e. they represent the Δχ² = 2.3, and 6.17 values). Middle and right: examples of fits to the SED within the 68% confidence level limits; the dusty disk model is displayed as a continuum line, the free-free power law for the gas emission as a dotted-dashed line, and the total model (dusty disk + free-free) as a dashed line, the flux upper limit at 6 cm as an arrow. The middle and right panels are for α_ff = −0.2 and 2.0, respectively.