SED of NGC 7027. Ancillary measurements, obtained with different instruments, are shown as open squares, while the Planck data are shown as red squares. The arrows indicate upper limits. The diamonds show the radio spectrum of NGC 7027 given by Zijlstra et al. (2008) and evolved to the mean Planck observing time. The continuous line is the model of the SED, obtained by combining both free-free (dashed line) and thermal dust emission (dotted line).