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G. D. Thompson, A. K. Speck, C. Dijkstra (University of Missouri - Columbia)
There have been several investigations of the evolution of the mid-infrared (IR) dust features in carbon star spectra based on IRAS LRS data, but these studies are somewhat contradictory. In order to understand these differences in interpretations and to develop an understanding of the carbon star dust sequence, we have reexamined 26 IRAS LRS spectra of carbon stars that have also been observed spectroscopically by ISO SWS. The low resolution of the IRAS LRS hinders the determination of the strength of the molecular absorptions due to HCN and C2H2 in these spectra. This has led to varying underestimations of the actual continuum levels in these spectra, which has a huge effect on the continuum-divided spectra used to analyze trends on the shape, strength, and position of the mid-IR features. The higher resolution of the ISO data and their broader wavelength coverage allow a more accurate fitting of the underlying continuum. We have therefore reassessed the trends in shape, strength, and position of the ~11\mum SiC feature, and the apparent emergence of the ~9\mum feature and find that there does not appear to be any correlation of these feature parameters with the temperature of the underlying continuum. In addition to looking for correlations between the continuum temperature, feature strength, and feature peak position, we also investigated whether any of these parameters correlate with the strength of the molecular bands. In all cases, no correlation was found. We discuss the implications of this study, in terms of both a carbon star condensation sequence and the application of this study to the larger IRAS dataset.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.