Ci in High-mass Star-forming Clouds
Abstract. We report measurements of the 12 C / 13 C abundance ratio in the three galactic regions G 333.0-0.4, NGC 6334 A and G 351.6-1.3 from observations of the 12 Ci 3 P2 → 3 P1 transition and the hyperfine components of the corresponding 13 Ci transition near 809 GHz. These transitions were obse...
| Main Authors: | , , , , , , , |
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| Other Authors: | |
| Format: | Text |
| Language: | English |
| Published: |
2001
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| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.314.8539 http://arxiv.org/pdf/astro-ph/0105176v1.pdf |
| Summary: | Abstract. We report measurements of the 12 C / 13 C abundance ratio in the three galactic regions G 333.0-0.4, NGC 6334 A and G 351.6-1.3 from observations of the 12 Ci 3 P2 → 3 P1 transition and the hyperfine components of the corresponding 13 Ci transition near 809 GHz. These transitions were observed simultaneously with the CO 7–6 line emission at 806 GHz with the AST/RO telescope located at the South Pole. From a simultaneous fit to the 12 Ci 3 P2 → 3 P1 transition and the HF components of the corresponding 13 Ci transition and an independent estimate of an upper limit to the optical depth of the 12 Ci emission we determine intrinsic 12 Ci / 13 Ci column density ratios of 23 ± 1 for G 333.0-0.4, 56 ± 14 for NGC 6334 A and 69 ± 12 for G 351.6-1.3. As the regions observed are photon dominated, we argue that the apparent enhancement in the abundance of 13 C towards G 333.0-0.4 may be due to strong isotope-selective photodissociation of 13 CO, outweighing the effects of chemical isotopic fractionation as suggested by models of PDRs. Towards NGC 6334 A and G 351.6-1.3 these effects appear to be balanced, similar to the situation for the Orion Bar region observed by Keene et al. (1998). Key words. ISM: abundances, atoms, clouds, H ii regions; Submillimeter 1. |
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