2001A&A...375L..23T -
Astronomy and Astrophysics, volume 375, L23-26 (2001/8-4)
13CI in high-mass star-forming clouds.
TIEFTRUNK A.R., JACOBS K., MARTIN C.L., SIEBERTZ O., STARK A.A., STUTZKI J., WALKER C.K. and WRIGHT G.A.
Abstract (from CDS):
We report measurements of the
12C/
13C 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
12CI
3P
2->
3P
1 transition and the hyperfine components of the corresponding
13CI 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
12CI
3P
2->
3P
1 transition and the HF components of the corresponding
13CI transition and an independent estimate of an upper limit to the optical depth of the
12CI emission we determine intrinsic
12CI/
13CI 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
13C towards G 333.0-0.4 may be due to strong isotope-selective photodissociation of
13CO, 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. (
1998ApJ...494L.107K).
Abstract Copyright:
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Journal keyword(s):
ISM: abundances - atoms - clouds - H II regions - submillimeter
Simbad objects:
7
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