13Ci in high-mass star-forming clouds

A. R. Tieftrunk, K. Jacobs, C. L. Martin, O. Siebertz, A. A. Stark, J. Stutzki, Christopher K Walker, G. A. Wright

Research output: Contribution to journalArticle

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Abstract

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 3P23P1 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 3P23P1 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. (1998).

Original languageEnglish (US)
JournalAstronomy and Astrophysics
Volume375
Issue number2
StatePublished - Aug 2001

Fingerprint

stars
isotopic fractionation
optical depth
isotope
fractionation
photodissociation
optical thickness
poles
isotopes
telescopes
augmentation
photons
estimates
effect
chemical

Keywords

  • Atoms
  • Clouds
  • H II regions
  • ISM: abundances
  • Submillimeter

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Tieftrunk, A. R., Jacobs, K., Martin, C. L., Siebertz, O., Stark, A. A., Stutzki, J., ... Wright, G. A. (2001). 13Ci in high-mass star-forming clouds. Astronomy and Astrophysics, 375(2).

13Ci in high-mass star-forming clouds. / Tieftrunk, A. R.; Jacobs, K.; Martin, C. L.; Siebertz, O.; Stark, A. A.; Stutzki, J.; Walker, Christopher K; Wright, G. A.

In: Astronomy and Astrophysics, Vol. 375, No. 2, 08.2001.

Research output: Contribution to journalArticle

Tieftrunk, AR, Jacobs, K, Martin, CL, Siebertz, O, Stark, AA, Stutzki, J, Walker, CK & Wright, GA 2001, '13Ci in high-mass star-forming clouds', Astronomy and Astrophysics, vol. 375, no. 2.
Tieftrunk AR, Jacobs K, Martin CL, Siebertz O, Stark AA, Stutzki J et al. 13Ci in high-mass star-forming clouds. Astronomy and Astrophysics. 2001 Aug;375(2).
Tieftrunk, A. R. ; Jacobs, K. ; Martin, C. L. ; Siebertz, O. ; Stark, A. A. ; Stutzki, J. ; Walker, Christopher K ; Wright, G. A. / 13Ci in high-mass star-forming clouds. In: Astronomy and Astrophysics. 2001 ; Vol. 375, No. 2.
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N2 - 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 3P2 → 3P1 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 3P2 → 3P1 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. (1998).

AB - 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 3P2 → 3P1 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 3P2 → 3P1 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. (1998).

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