Abstract
The circumstellar dust in R CrB stars is often thought to be due to graphite, because of the high carbon abundance in the stars. Further, the spectra of these stars in the infrared show feature-less smooth continuum (Forrest 1974, Roche and Aitken 1984) which was also thought to be characteristic of graphite. However, the recent comparison of the ultraviolet spectra obtained at maximum and minimum light of R CrB showed an extinction peak in the region of 2400 to 2500A (Holm, Wu & Doherty 1982, Hecht et al. 1984) which was identified as due to amorphous or glassy carbon particles. According to Duley and Williams (1981,83) amorphous carbon is supposed to show spectral features in the 3.3-3.4 μm region. Further many dust emission features are also supposed to appear in the spectral region 3 to 3.5 μm (Aikten 1981). The previous studies in this spectral region in R CrB (Forrest 1974) and in the hotter star V348 Sgr (Allen et al. 1982) showed smooth continuum. V348 Sgr shows spectroscopically many similarities with other WC 11 stars and was grouped with CPD-56°8032, He 2-113 and M4-18 (Webster and Glass 1974). All these three stars show strong dust emission features at 3.3, 8.6 11.25 μm. With a view to search for weaker dust spectral features we obtained the spectrum of R CrB and V348 Sgr with higher resolution than employed before.
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