The Infrared Emission Features in the Spectrum of the Wolf-Rayet star WR 48a

Abstract

We present the first detection of unidentified infrared (UIR) emission features at ~6.4 and 7.9 μm in the spectrum of the dusty WC8 Wolf-Rayet star WR 48a. Based on the H-deficient nature of WC stars, we attribute the emission features to large carbonaceous molecules or amorphous carbon dust grains in the circumstellar environment of WR 48a. The 6.4 μm feature resembles the emission feature seen toward H-deficient planetary nebulae (PNe), while the 7.9 μm profile resembles that of some PNe with H-deficient WC10 central stars. These similarities point toward a similar origin of the dust in these H-deficient environments and highlights the apparent sensitivity of the UIR bands to physical conditions. In the case of WR 48a and the [WC10] PNe, shock processing may play a major role in dust formation. Based on observations made with the Infrared Space Observatory, an ESA project with instruments funded by ESA member states (especially the PI countries: France, Germany, the Netherlands, and the United Kingdom) and with the participation of ISAS and NASA.