The following document lists the file abstract/ICHERCHN_RCBDUST.abs
from catalogue VI/111.
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R Coronae Borealis (R CrB) stars are a small group of low-mass, hydrogen-deficient, carbon stars, characterized by sudden drops in stellar brightness. These periodical fadings are attributed to obscuration by ejected puffs of gas from the stellar surface and along the line of sight, in which dust grains condense. The extinction curves of two R CrB stars during a decline event could be well fitted by a distribution of amorphous carbon (AC) grains (Hecht 1984). However, the physical conditions in R CrB outflows are harsh compared with other stellar environments where similar dust condenses (e.g., AGB stars), and the chemical processes responsible for the formation of AC dust precursors in a hydrogen- poor gas are not yet well understood. As for carbon-rich Wolf- Rayet (WC) stars, dust is expected to nucleate from a pure carbon phase, leading to the formation of carbon chain molecules (C2-C9), polycyclic aromatic carbon (PAC) molecules, and fullerene (C60) species as dust precursors. This chemical pathway to dust is supported by the observations of C2 and C3 absorption bands in a R CrB star during minimum light. We propose observing for the first time several IR signatures of dust progenitors with the Short Wavelength Spectrometer, to shed light on the process of dust formation in R CrB winds. The targets selected are amongst the brightest R CrB star in the IR. We plan observing the 6.2 and 7.7 mu C-C stretching band of the PAC skeleton to confirm the presence of PACs as dust precursors. We also propose observing the 7.1 and 8.5 mu vibrational emission bands of gas-phase C60. We believe that these novel observations, besides providing clues on the dust condensation route in R CrB winds, will highlight for the first time a type of astrophysical objects in which fullerene species form.