The formation of silicon-carbon chain molecules in IRC+10216

T. J. Millar

doi:10.1093/mnras/stag2050

paper

The formation of silicon-carbon chain molecules in IRC+10216

arXiv:2610.36369 · doi:10.1093/mnras/stag2050

Abstract

Linear silicon-carbon chain molecules, SiC $_{n}$ (n = 3--6), have been detected in the circumstellar envelope of the carbon-rich AGB star IRC+10216. Here, we discuss the mechanisms likely to be at work in the synthesis of chains up to SiC $_{8}$ and present for the first time a detailed comparison between observations and model calculations. Using a combination of measured and postulated rate coefficients, we show that the column densities of the silicon carbide molecules observed in IRC+10216 can be reproduced to with a factor of four. Furthermore, our model calculations suggest that the column densities of SiC $_{7}$ and SiC $_{8}$ are a factor of 2--4 less than that of SiC $_{6}$ . We discuss the influence of neutral-neutral reactions involving parent SiC $_{2}$ on chain growth and show that their neglect leads to a reduction in column densities of carbides up to a maximum of about six for SiC $_{6}$ and SiC $_{7}$ . Our results suggest that the detection of SiC $_{7}$ and SiC $_{8}$ in IRC+10216 will be challenging but that astronomical searches should be undertaken.

arXiv commentAccepted for publication in MNRAS, 9 pages including one appendix