Millimetre and submillimetre continuum observations of planetary nebulae.

Continuum emission from a total of 13 PN has been detected at millimeter and submillimeter wavelengths, in all but one case for the first time. It was found that type I and young, compact PN both have significant dust emission at 450 and 800 microns, while at 1100 and 2000 microns the free-free emission from the nebular gas dominates. More evolved PN do not usually show any cool dust excess above the free-free emission at 800 microns. The cool dust in the neutral regions surrounding NGC 7027 and BD + 30 deg 3639 was spatially resolved. The IR submillimeter observations for NGC 7027 and BD + 30 deg 3639 are modeled using amorphous carbon dust, graphite not being able to provide enough submillimeter flux. In the ionized regions of these two young, compact nebulae it is deduced that the dust-to-gas ratios are no higher than about 0.0007. It is concluded that dust is not significantly destroyed in the ionized region of the nebula.