HIGH-RESOLUTION FAR-INFRARED OBSERVATIONS OF THE RING-NEBULA

High spatial resolution 50 and 100 mu m observations of the Ring Nebul a reveal a far-infrared emission peak close to the center of the nebul a where atomic and molecular emission is at a minimum. Dust in this ce ntral peak emission region is heated by direct absorption of radiation from the central star. While the dust temperature in the central peak region is about 50 K (dust emissivity index of 1.5), the temperature of the bulk of the dust located in the regions of the ionized nebular core and the neutral molecular gas is on average lower than 50 K. Ly a lpha photons are sufficient for heating the dust grains within the neb ular core. Far-infrared emission is also found from grains mixed with the molecular gas outside the main ionized nebular core.