Sub-millimeter SED of the Fomalhaut debris disk. Data at 0.35, 0.45, 0.85 are from Marsh et al. (2005) and Holland et al. (2003); the plotted uncertainties for these data are 20%, 20%, and 15% of the measured flux, respectively; the data point at 1.3 mm from Chini et al. (1991) is taken as a lower limit and is not considered for the fit (Sect. 3.2); the blue data-point indicates the integrated flux density at 6.66 mm from this paper. The value of the spectral index measured between 0.35 and 6.66 mm is also shown in blue.