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Session 97 - Planetary Nebulae.
Display session, Thursday, January 16
Hydrogen-poor planetary nebulae offer an exceptional opportunity to advance our knowledge of the physical nature, size distribution, and evolution of carbonaceous dust grains. The inner ejecta of these objects have a high dust to gas ratio (approaching 1/5) with the consequence that the thermal dust continuum is not confused by line emission from the gas. The recently launched Infrared Space Observatory (ISO) provides an opportunity to observe the thermal dust emission over the important 2-200\mum wavelength range, complementing our ongoing program of comprehensive observations of the five known members of this class of PNe.
Abell 78 is of special interest because it is bright and extended, and is similar to the extensively studied Abell 30. Unfortunately, A78 was never observed by IRAS, so its far IR spectrum was unknown. In this poster we present results of our observations of A78 with all four ISO instruments: LWS, SWS, PHOT and CAM. In addition to total fluxes, we compare the dust distribution seen in the ISOCAM images at \lambda \leq 15\mum with the distribution of H-poor gas seen in HST images. We find an alignment between the ISOCAM dust map and the ring of H-poor knots seen by HST. This is similar to the alignment seen in A30 between its H-poor ring and the near IR K-band images.
Program listing for Thursday