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. Carbon-rich dust heated
by hot stars often displays emission in the familiar UIR bands, e.g.
NGC 7027 or other C-rich 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 6000-8000 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 ground-based and/or IRAS LRS spectra. These consist of
an F-type post-AGB 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 15194-5115, the third-brightest carbon star in the infrared sky.
The F-type post-AGB object IRAS 05341+0852 shows a strong broad emission
complex at 11-13 microns, together with weaker features near 10.5 microns
and a prominent emission peak near 21 microns. Ground-based 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 the whole
2.4 - 45 micron region of these intriguing objects