The following document lists the file abstract/JHARRING_HPOORPNE.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
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 has an extraordinarily 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. This is true even in the 3 - 10 micron region, where the dust emission is due to the stochastic heating of small carbon clusters. Using the available ground-based and IRAS data, we have already demonstrated for one of these objects - Abell 30 - that is is feasible to model the entire IR spectrum from 2 - 200 microns and in the process derive the (dust/gas) ratio, the minimum grain size, and the slope of the size distribution, i.e., the ratio of small to large grains. With ISO data we will be able determine these parameters more precisely and for all the known members of this class. Since the known H-poor planetaries form an evolutionary sequence, we will thus be able to determine whether and how dust evolves with time in these nebulae. Another important objective of this study is to look for emission features, such as the C-C stretch, which the small amorphous carbon clusters may produce. The smallest grains in the H-poor planetaries are expected to differ from those in normal planetaries because they formed in the absence of hydrogen, and we would not find PAHs, for example. The high sensitivity and spectral resolution of ISO will allow us to search for any such features. Finally, the imaging capabilities of ISO will allow us, for the largest of these objects, to map the grain properties as a function of position in the nebula. This will allow us to test models of heating and to study the transport of dusty ejecta by mass-loading of the stellar wind from the central star. This later application will complement our ongoing study of the morphology of the H-poor planetaries with the Hubble Space Telescope.