Coma dust spectrum of comet 8P/Tuttle, continuum divided and normalized to unity at 13.0 μm. The red line corresponds to a smoothing over the data points, with a smoothing window of 15 data points. The red error bars correspond to the variance of the data points within the smoothing window. The blue line shows the spectrum in the SL mode assuming a single temperature for the dust coma, which causes the continuum to be overestimated around 8 μm (see text fordetails).