Model of the SED of CRL 618 (continuous line) considering both free-free (dashed line) and thermal dust emission (dotted line). Ancillary measurements, obtained with different instruments (IRAS, Helou & Walker 1988; Akari, Murakami et al. 2007), are shown as open squares, while Planck data are shown as red squares. The arrows indicate upper limits. For the ancillary radio measurements (ν ≤ 40 GHz) only VLA data coeval to Planck observations have been used (see text).