Spectral energy distribution of the radio continuum emission of CRL 618. The colors indicate the data from the same epoch, as is shown in the upper left corner of the figure. The dashed line corresponds to model calculations for the epoch 1998 (see main text). The dot-dashed line corresponds to model calculations for the epoch 1982 (see main text). The data at wavelengths  <5 mm were taken from Kwok & Feldman (1981; extrapolation to epoch 1982); Martín-Pintado et al. (1988; epoch 1987), Reuter et al. (1997; epoch 1995); Sánchez-Contreras & Sahai (2004; extrapolation to epoch 1998).