Table 4
Comparison of CCH and c-C3H2 abundances in different PDRs.
| G0 | nH2[ cm-3] | X(CCH)* | X(c-C3H2)* | N(c-C3H2)/N(CCH) | References | |
|
|
||||||
| MonR2 | ||||||
|
|
||||||
| MonR2 IF | 5.7 × 10-9 | 3.5 × 10-11 | 0.006 | (a), (b) | ||
| MonR2 MP2 | 2.6 × 10-9***** | 7.6 × 10-11** | 0.029*** | (a), (b) | ||
| MonR2 PDR | 5 × 105 | 3 × 106 | 1.7 × 10-8 | 1.4 × 10-10 | 0.008 | a |
| MonR2 env | 1–100 | 5 × 104 | 3.5 × 10-9 | 1.4 × 10-11 | 0.004 | (a) |
| MonR2 red wing | 1.8 × 10-8 | 7.8 × 10-10 | 0.04 | (a) | ||
|
|
||||||
| Other PDRs | ||||||
|
|
||||||
| Horsehead | 100 | 1 × 105 | 1.4 × 10-8 | 1.1 × 10-9 | 0.08 | (c) |
| Oph-W | 400 | 2 × 104 | 6.0 × 10-9 | 6.0 × 10-10 | 0.1 | (d) |
| IC 63 | 1500 | 1 × 105 | 1.1 × 10-8 | 9.0 × 10-10 | 0.08 | (d) |
| NGC 7023 | 2600 | 104 − 106 | 6.0 × 10-9 | 2.0 × 10-10 | 0.03 | (e), (f), (g) |
| Orion Bar | 2 × 104 | 1 × 105 | 2.0 × 10-9 | 3.8 × 10-11 | 0.01–0.03 | (f), (h), (i) |
Notes.
The uncertainty in the abundances is driven by the uncertainty in the H2 gas column density, which is assumed to be a factor of 2.
Calculated using the C18O observations of Ginard et al. (2012) as reference for the H2 gas column density: N(C18O) = 1.3 × 1016 cm-2.
In MP2, we have to rely only on the 3 mm and 1 mm transitions of CCH. Thus, we may underestimate the CCH column density (and consequently, overestimate N(c-C3H2)/N(CCH)) by a factor of 2.
Reference. (a) this work; (b) Ginard et al. (2012); (c) Pety et al. (2005); (d) Teyssier et al. (2004); (e) Fuente et al. (1993); (f) Fuente et al. (2003); (g) Pilleri et al. (2012b); (h) Ungerechts et al. (1997); (i) Fuente et al. (1996).
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