The following document lists the file abstract/KVOLK_11MICRON.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
The IRAS Low Resolution Spectrometer (LRS) observations detected many sources with the 11.3 micron emission feature attributed to SiC dust. Nearly all of these sources are associated with known carbon stars, and their LRS spectra show an underlying continuum which rises steeply to the short wavelength end of the LRS range. The carbon stars with the thickest dust shells, such as IRC+10216 and AFGL 3068, show either weak 11.3 micron emission or possibly a very weak 11.3 micron absorption. No known carbon star has 11.3 micron absorption, in contrast to the case of the 10 and 18 micron silicate features which are observed in absorption for some stars. It is puzzling that carbon stars which have dust shells of very high optical depth do not show any strong emission or absorption features. In the set of LRS spectra there are four sources with possible unusual 11.3 micron features. One thing that makes them unusual is that the LRS spectra have very low colour temperature continua (similar to that of AFGL 3068). Unlike all accepted extreme carbon stars these four sources show strong 11.3 micron features. In two cases a normal shaped, strong 11.3 micron emission feature appears to be present on the cool continuum. In the other two cases there is what looks like a strong 11.3 micron absorption and a companion broad absorption feature between 16 and 23 microns (which is NOT the 18 micron silicate feature). These sources have no known associations. We request SWS and LWS observations of these sources to verify their 11.3 micron features, to search for additional features, and to detect their central stars if possible. A detailed study of the 11.3 micron feature shape compared to that of a typical carbon star will allow us to tell whether this feature is due to SiC or to some exotic type of dust. Fitting the spectra with radiative transfer models will allow the dust shell properties to be determined.