Infrared Space Observatory spectra of R Coronae Borealis stars. I. Emission features in the interval 3-25 microns

Infrared Space Observatory 3-25 mum spectra of the R Coronae Borealis stars V854 Cen, R CrB, and RY Sgr are presented and discussed. Sharp emission fe atures coincident in wavelength with the well-known unidentified emission f eatures are present in the spectrum of V854 Cen but not in the spectra of R CrB and RY Sgr. Since V854 Cen is not particularly hydrogen-poor and has 1 000 times more hydrogen than the other stars, the emission features are pro bably from a carrier containing hydrogen. There is a correspondence between the features and the emission from laboratory samples of hydrogenated amor phous carbon. A search for C-60 in emission or absorption proved negative. Amorphous carbon particles account for the broad emission features seen bet ween 6 and 14 mum in the spectrum of each star.