Flux density measured from S255 NIRS 3 as a function of frequency (points). The curves represent the best fits to the different epochs obtained with the model by Reynolds (1986). Symbols with the same colour correspond to the same epoch, as explained in the figure. The black point at 225 GHz is the measurement by Zinchenko et al. (2012). The dashed line denotes the expected mm emission according to Eq. (4). The vertical error bars correspond to the calibration uncertainty, while the horizontal bars indicate the frequency ranges covered by the VLA correlator at the different bands.