IRAS sources beyond the solar circle. VII. The ^12^C/^13^C ratio in the far outer Galaxy.

Details IRAS sources beyond the solar circle. VII. The ^12^C/^13^C ratio in the far outer Galaxy. IRAS sources beyond the solar circle. VII. The ^12^C/^13^C ratio in the far outer Galaxy.

Nov 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26as..119..439w&link_type=abstract

Astronomy and Astrophysics Supplement, v.119, p.439-457

Astronomy and Astrophysics

Astrophysics

13

Ism: Abundances, Ism: Molecules, Galaxy: Abundances, Radio Lines: Ism

Scientific paper

We have investigated the ^12^C/^13^C abundance ratio in the far-outer Galaxy. We have used the IRAM 30-m telescope to obtain the ^12^CO and ^13^CO(1-0) and (2-1) distributions towards five IRAS sources at about 16-17 kpc from the galactic center. C^18^O(1-0) and (2-1) were observed towards the ^13^CO peak positions in those clouds. The source with the strongest C^18^O emission, WB 89-437, was subsequently observed in ^13^C^18^O(1-0) and (2-1) and in H_2_CS(3_1,2_-2_1,1_) and (6_1,5_-5_1,4_). To be able to compare our results with published data, we observed the same transitions towards the inner Galaxy source W 33, and towards W 3OH. The ratio of the ^13^CO and C^18^O column densities is about 14, slightly larger than what was found in local GMCs. This ratio is dominated by excitation and beam filling effects, and is therefore not indicative of the abundance ratios. The ratio C^18^O(1-0)/^13^C^18^O(1-0) directly yields the ^12^C/^13^C abundance ratio however, for which towards WB 89-437 we find a 3σ lower limit of 201+/-15, which means that the ^12^C/^13^C gradient found in the inner Galaxy continues further out. Our results for W 33 and W 3OH are consistent with earlier observations and give abundance ratios of 43.0+/-4.3 and 85+/-15, respectively. These J=1-0 measurements are however in contrast to results obtained from the corresponding J=2-1 transitions: we obtain abundance ratios of 104+/-60 (WB 89-437), 31+/-2 (W 33), and 24+/- 2 (W 3OH). These differences may be due to the emission of the two transitions originating in different parts of the cloud with different excitation conditions. The ^12^CO emission towards WB 89-437 shows strong outflow emission, and that of WB 89-380 is dominated by self-absorption. The sizes of the ^13^CO clumps are 1-2pc and they have peak positions located within 10" (0.5pc) from the IRAS position. Their (virial) masses are typically several 1000Msun_ .

Affiliated with

Also associated with

No associations

Rating

IRAS sources beyond the solar circle. VII. The ^12^C/^13^C ratio in the far outer Galaxy. does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with IRAS sources beyond the solar circle. VII. The ^12^C/^13^C ratio in the far outer Galaxy., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and IRAS sources beyond the solar circle. VII. The ^12^C/^13^C ratio in the far outer Galaxy. will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1145371