Carbon Isotope Ratio in 12CO/13CO toward Local Molecular Clouds with Near-Infrared High-Resolution Spectroscopy of Vibrational Transition Bands

Details Carbon Isotope Ratio in 12CO/13CO toward Local Molecular Clouds with Near-Infrared High-Resolution Spectroscopy of Vibrational Transition Bands Carbon Isotope Ratio in 12CO/13CO toward Local Molecular Clouds with Near-Infrared High-Resolution Spectroscopy of Vibrational Transition Bands

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003apj...598.1038g&link_type=abstract

The Astrophysical Journal, Volume 598, Issue 2, pp. 1038-1047.

Astronomy and Astrophysics

Astronomy

12

Infrared: Ism, Ism: Abundances, Ism: Clouds, Ism: Lines And Bands, Ism: Molecules, Stars: Individual: Alphanumeric: Afgl 490, Stars: Individual: Alphanumeric: Lkhα 101, Stars: Individual: Constellation Name: Monoceros R2 Irs 3

Scientific paper

We report the carbon monoxide isotope ratio in local molecular clouds toward LkHα 101, AFGL 490, and Mon R2 IRS 3. The vibrational transition bands of 12CO ν=2<--0 and 13CO ν=1<--0 were observed with high-resolution near-infrared spectroscopy (R=23,000) to measure the 12CO/13CO ratio. The isotopic ratios are 12CO/13CO=137+/-9 (LkHα 101), 86+/-49 (AFGL 490), and 158 (Mon R2 IRS 3), which are 1.5-2.8 times higher than the local interstellar medium value of 12CO/13CO=57+/-5 from millimeter C18O emission observations. This is not easily explained by saturation of the 13CO absorption. It is also questionable whether the selective photodestruction of 13CO can account for the difference between the Galactic trend and the present observation, because the molecular clouds are with high visible extinction (AV=10-70 mag), well shielded from destructive FUV radiation. The molecular gas associated with AFGL 490 and Mon R2 IRS 3 consists of multiple temperature components lying in the lines of sight. In the cool component (Tex<100 K), the excitation temperature of 12CO is twice that of 13CO. We attribute the temperature discrepancy to the photon-trapping effect, which makes the radiative cooling of the main isotopomer less effective.
Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

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