Table 9
Isotopic ratios derived from LTE column densities of CIT 6 and IRC+10216 (this work), with benchmarks.
| Ratio | Tracer (type) | CIT 6 | ± | IRC+10216 | ± | Solar | Local ISM | Notes |
|---|---|---|---|---|---|---|---|---|
| 32S/34S | N(CS)/N(C34S) | 23.4 | 9.9 | 25.3 | 10.8 | 22.1 | 20.0 | Optically thick CS; uncertainty ∼ 30% |
| 28Si/29Si | N(SiO)/N(29 SiO) | 10.9 | 4.6 | 18.5 | 7.9 | 19.7 | − | SiO possibly thick; SiS ratios often closer to solar |
| 12C/13C | N(CS)/N(13 CS) | 18.1 | 7.7 | 13.0 | 5.5 | 89.4 | 54.0 | Apparent; CS often optically thick |
| 12C/13C | N(HC3N)/N(H13 CCCN) | 29.8 | 8.3 | 18.0 | 5.0 | 89.4 | 54.0 | − |
| 12C/13C | N(HC3N)/N(HC13 CCN) | 19.6 | 5.5 | 19.8 | 5.5 | 89.4 | 54.0 | − |
| 12C34S/13C32S | N(C34S)/N(13 CS) | 0.52 | 0.16 | 0.36 | 0.11 | − | − | Optically thin product ratio |
| 12C/13C (inferred) | thin pair +32 S/3 S = 22.1 | 11.5 | 3.6 | 8.0 | 2.5 | 89.4 | 54.0 | From Eq. (6); opacity-independent |
Notes. App. denotes apparent ratios derived using a main isotopologue (lower limits if optically thick). Optically thin pair ratios only use rare isotopologues and are largely insensitive to opacity. The thin-pair value 12C34S/13C32S is converted to an inferred 12C/13C adopting 32S/34S = 22.1 (Asplund et al. 2009). Benchmarks: solar isotopic ratios from Asplund et al. (2009); representative local ISM 12C/13C = 54 ± 10 from Yan et al. (2023). Apparent ratios are lower limits when the main isotopologue is optically thick. See text for discussion of Si and C isotopes and for thin-thin comparisons (Kahane et al. 1988; Cernicharo et al. 2000; Fonfría et al. 2015).
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