Circumstellar carbonaceous material associated with late-type dusty WC Wolf-Rayet stars

We have studied the 5-8.5 mum infrared spectra of the late-type Wolf-Rayet stars WR 118, WR 112, and WR 104, the WN star WR 147, the B5 hypergiant Cyg nus OB2 No. 12, and the Galactic center luminous blue variable Pistol Star using the Short Wavelength Spectrometer on the Infrared Space Observatory. We attribute an absorption feature at 6.2 mum in the spectra of WC stars to amorphous carbon dust. This absorption feature is not detected in the diff use interstellar medium toward the WR 147, Cyg OB2 No. 12, or the Pistol St ar, and therefore we suggest that it is circumstellar in nature. In additio n, we detect a broad absorption feature extending from approximately 6.5 to 8 mum. We tentatively attribute this absorption to the C-C stretching mode s that accompany the 6.2 mum band in aromatic materials. Our analysis of th e 6.2 mum absorption profile suggests that the dust grains have to be rathe r large (similar to1 mum) and point toward dense clumps as the sites of dus t formation.