SPECTRAL FEATURES IN CARBON-RICH STELLAR ENVELOPES

in this proposal, more time is being requested for proche.stardust we propose to include one previously unavailable target from the spring list, upgrade one grade 3 source and add four new sources. infrared spectra of dusty stellar envelopes reflect the abundances of dust grains and/or large molecules in the circumstellar material and the effects of the stellar radiation field. carbonrich dust heated by hot stars often displays emission in the familiar uir bands, e.g. ngc 7027 or other crich planetary nebulae (although significant differences in relative intensities and band profiles are evident from source to source). in contrast some dusty envelopes around cooler stars (in the range 60008000 k) display peculiar emission spectra which appear to be related to the uir emission bands, but which may arise from species that do not survive the harsher radiation fields of the hotter stars, and may therefore represent emission from much more fragile carbon clusters. we wish to use the sws to investigate the detailed dust emission spectra of a sample of stars which have been found to have peculiar ir spectral features from groundbased and/or iras lrs spectra. these consist of an ftype postagb star, a carbon star/a star binary system, and three carbon stars recently discovered to show the silicon carbide feature in absorption. in addition, we propose to obtain an lws01 spectrum of the brightest of the sic absorption sources, and an lws01 spectrum of iras 151945115, the thirdbrightest carbon star in the infrared sky. the ftype postagb object iras 05341+0852 shows a strong broad emission complex at 1113 microns, together with weaker features near 10.5 microns and a prominent emission peak near 21 microns. groundbased spectra show evidence of substructure in the 21 micron band; we wish to follow this up with a maximum resolution sws01 spectra in order to resolve this substructure. iso provides the only way to sample truncated!, [truncated!, Please see actual data for full text]