==> In this proposal, more time is being requested for BHRIVNAK.SWSPPN01
==> This proposal requests an upgrade from Priority 3 for BHRIVNAK.SWSPPN01
The goal of this proposal is to determine the chemical properties of the dust
shells of proto-planetary nebulae through a study of their short-wavelength
infrared spectra.  Four sources comprise the original priority 2 proposal, and
a few PPN have been observed by others on GTO proposals.  In this proposal, we
request additional observations to obtain a representative sample of both
oxygen and carbon-rich sources; in this way, we will be able to determine the
general properties of the dust shells of these transitional objects.
Spectra in the wavelength interval 2.5 to 45 microns cover the regions which
contain features in both oxygen-rich (9.7 microns and ISO-discovered features
at 20-45 microns) and carbon-rich (21 and 30 micron and PAH features) objects.
We propose to observe both types.  They all have visible counterparts, and we
have extensive supporting ground-based observations of each of these.