SPECTROSCOPY OF VISIBLE PROTO-PLANETARY NEBULAE

the goal of this proposal is to determine the chemical properties of the dust shells of protoplanetary nebulae (ppn) through a study of their shortwavelength, and in a few cases their longwavelength, infrared spectra. spectral features in the 10 to 20 micron region indicate the chemical nature (oxygen or carbonrich), and the strengths of the features relate to the physical properties of the shells. a few bright carbonrich 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 for which we have confirmed a visible counterpart. these we have observed extensively from the ground visible photometry, near infrared photometry, visible spectroscopy and are well prepared to interpret the infrared spectra of these objects in the context of their overall properties. this study will greatly advance our understanding of this important evolutionary stage. only iso provides the spectral range and resolution necessary to carry out these observations. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]