The following document lists the file abstract/BHRIVNAK_SWSPPN02.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
The goal of this proposal is to determine the chemical properties of the dust shells of obscured proto-planetary nebulae (PPN) through a study of their short-wavelength infrared spectra. Spectral features in the 10 to 20 micron region indicate the chemical nature (oxygen or carbon-rich), and the strengths of the features relate to the physical properties of the shells. A few carbon-rich PPN have been observed to show PAH features and an unidentified 21 micron emission feature. We propose to observe a sample of IRAS sources which have the expected properties of PPN and which have no visible counterparts (V>20 mag). These we have located and observed from the ground, obtaining near- and mid-infrared photometry. Essentially all previously studied PPN have visible counterparts. Compared with these, we believe this sample of invisible PPN are obscured either because they had a higher mass-loss rate on the AGB or because they are less evolved post-AGB objects and their shells have not yet expanded sufficiently for visible light to escape. In either case, this study will allow us to investigate a sample of PPN at a different state of evolution from other PPN studied, which have visible counterparts of G-A spectral types. This will advance our understanding of the range and evolution of the properties of circumstellar shells in this important evolutionary stage. Only ISO provides the spectral range and resolution necessary to carry out these observations.