We present millimetre photometry and submillimetre imaging of the central core and two hotspots in the radio lobes of the galaxy Cygnus-A .
For both hotspots and the central core the synchrotron spectrum continues smoothly from the radio to a frequency of 677 GHz .
The spectral index of the hotspots is constant over our frequency range , with a spectral index of \alpha \approx - 1.0 ( S _ { \nu } \propto \nu ^ { \alpha } ) , which is steeper than at lower frequencies and represents the emission from an aged population of electrons .
The core is significantly flatter , with \alpha = -0.6 \pm 0.1 , suggestive of an injected spectrum with no ageing , but some evidence for steepening exists at our highest observing frequency .
Although IRAS data suggest the presence of dust in Cygnus-A , our 450 \mu { m } data show no evidence of cold dust , therefore the dust component must have a temperature lying between 85 K and 37 K , corresponding to dust masses of 1.4 \times 10 ^ { 6 } M _ { \odot } and 1.0 \times 10 ^ { 8 } M _ { \odot } respectively .