The following document lists the file abstract/ICHERCHN_WCDUST.abs
from catalogue VI/111.
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Late-type carbon-rich Wolf-Rayet (WC) stars are persistent or episodic dust makers. The infrared (IR) excess emission due to dust has long been observed via IR photometry and is attributed to amorphous carbon (AC) grains forming in the stellar wind. However, physical conditions in the outflow are harsh compared with other stellar environments where dust condenses (e.g., AGB stars), and the chemical processes responsible for the formation of dust precursors and grains are not yet well understood. The WC winds are ionized, carbon and helium-rich, and hydrogen-poor. Therefore, dust is expected to nucleate from a ionized and neutral pure carbon phase, leading to the formation of carbon chain molecules, polycyclic aromatic carbon (PAC) molecules, and fullerene (C60) species as dust precursors. This chemical pathway to dust condensation was supported by KAO observations of the 7.7 mu C-C stretching mode of the PAC skeleton in two WC stars. We propose observing several IR signatures characteristic of dust precursor species with the Short Wavelength Spectrometer, to shed light on the process of dust formation in WC winds. The targets selected are amongst the brightest WC stars in the IR, and a representative of dust-forming stars. We plan to observe the 7.7 mu PAC emission band to extend the KAO results to a larger sample of Wolf-Rayet stars, and to observe the 6.2 mu C-C stretching band to confirm the presence of PACs as dust precursors. We also propose to observe the 7.1 and 8.5 mu vibrational emission bands of gas- phase fullerene (C60). We believe that these SWS observations, besides providing clues on the dust condensation route in WC winds and guidance to theoretical studies, will highlight for the first time astrophysical environments in which fullerene species form, and will provide informations on the origin of interstellar C60.