The following document lists the file abstract/IREID_COCLMC.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
We propose to use the Short Wavelength Spectrometer to observe a sample of highly-obscured asymptotic giant branch stars in both the LMC and the SMC. These stars, which have been identified through near-IR follow-up observations of IRAS sources, are in the process of evolving from the AGB to become planetary nebulae. Although the classical limit to AGB evolution is M(bol)=-7.1, these giants have bolometric magnitudes as low as -6. The aim of our observations is to determine whether these stars have the 11.6 micron SiC emission that characterises carbon-rich stars, or the broad 10 and 18 micron emission features of the O-rich M-type stars. This is of particular interest since, although carbon stars are common amongst the lower-luminosity AGB stars, very few are found brighter than M(bol)=-6, despite the theoretical expectation that the brighter, more massive stars should be more efficient at synthesising carbon. It is possible that envelope-burning may be responsible for maintaining C < O, but another possibility is that the higher opacity in C-rich envelopes may truncate AGB evolution through high mass-loss, thereby accounting for the general scarcity of luminous AGB stars. In the latter case, we would expect the highly-obscured, cocoon stars to have C-rich dust shells. Since all of our sample are optically invisible, ISO represents the only method of determining the chemical composition of the circumstellar dust-shells.