The following document lists the file abstract/CZHANG_DUSTY_PN.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
From the early days of infrared observations it has been known that the planetary nebulae (PNs) have significant dust emission in the far- infrared. For well observed IRAS sources on the average about 30% of the total bolometric flux of PNs comes from the dust component. It is clear that the circumstellar dust is the remnant of the dust shell from the preceding red giant phase, but there is considerable uncertainty about where the dust emission is coming from because it has been argued that the dust will be destroyed on short time scales in the ionized region while observations suggest that the dust is mixed into the ionized region. Studies of a few carbon-rich PNs have indicated that the dust to gas mass ratio is smaller in PNs than in carbon stars or the interstellar medium. However the depletion of Ca and some other refractory elements suggests that the dust cannot be destroyed. It might be ejected from the ionized zone by radiation pressure. It is desirable to study the dust in PNs to understand its properties and try to resolve these questions. One aspect of this is the proposal to image some PNs in dust emission to see if the dust is in the ionized region. In this proposal we seek detailed spectroscopy of the dust emission in selected PNs with strong dust emission. The spectral information which the SWS and LWS instruments can provide will for the first time fully characterize the dust emission in these PNs. Using radiative transfer and photoionization models of the dust and nebular emission should allow us to deduce the radial temperature distribution of the dust and find the dust to gas mass ratios for these objects. We wish to study young PN with the UIE features and sources with silicate dust to compare with the older PNs studied previously in the literature. In particular no disk PN with strong silicate dust emission has previously been studied in this manner, so this project will fill a gap in our knowledge of these objects.