Infrared Space Observatory Spectra of R Coronae Borealis Stars. I. Emission Features in the Interval 3-25 Microns

Abstract

Infrared Space Observatory 3-25 μm spectra of the R Coronae Borealis stars V854 Cen, R CrB, and RY Sgr are presented and discussed. Sharp emission features coincident in wavelength with the well-known unidentified emission features 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 1000 times more hydrogen than the other stars, the emission features are probably from a carrier containing hydrogen. There is a correspondence between the features and the emission from laboratory samples of hydrogenated amorphous carbon. A search for C60 in emission or absorption proved negative. Amorphous carbon particles account for the broad emission features seen between 6 and 14 μm in the spectrum of each star. Based on observations with ISO, an ESA project with instruments funded by ESA member states (especially the PI countries: France, Germany, the Netherlands, and the UK) and with the participation of ISAS and NASA.