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PreprintCC BY 4.0arXiv

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

  • T. J. Millar
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Abstract

Linear silicon-carbon chain molecules, SiCn (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 SiC8 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 SiC7 and SiC8 are a factor of 2--4 less than that of SiC6. We discuss the influence of neutral-neutral reactions involving parent SiC2 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 SiC6 and SiC7. Our results suggest that the detection of SiC7 and SiC8 in IRC+10216 will be challenging but that astronomical searches should be undertaken.

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Cite

BibTeXRIS
BibTeX
@misc{millar2026formation,
  title = {{The formation of silicon-carbon chain molecules in IRC+10216}},
  author = {T. J. Millar},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.36369},
  eprint = {2610.36369},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.36369},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - The formation of silicon-carbon chain molecules in IRC+10216
AU  - T. J. Millar
PY  - 2026
DA  - 2026/10/26
PB  - arXiv
DO  - 10.48550/arxiv.2610.36369
UR  - https://arxiv.org/abs/2610.36369
AB  - 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.
ER  -