The [TSUP]12[/TSUP]C/[TSUP]13[/TSUP]C Isotopic Ratio in Photodissociated Gas in M42

Abstract

We have observed the 158 µm 2 P 3 2 ← 2 P 1 2 fine-structure line of 12 C II simultaneously with the F = 2 ← 1 and F = 1 ← 0 hyperfine components of this transition in 13 C II in the Orion photodissociation region near θ 1 C. The line profiles were fully resolved using a heterodyne spectrometer with 0.5 km s −1 resolution. The relative intensities of these lines give a 12 C/ 13 C isotopic ratio of R = 58 ( +6 −5 ) for the most probable 12 C II peak optical depth τ = 1.3 . The constrained range of τ ( 12 C II) between 1.0 and 1.4 corresponds to a range of 12 C/ 13 C between 52 and 61. The most probable value of 58 agrees very well with that obtained from a relationship between the isotopic ratio and galactocentric distance derived from CO measurements, but is lower than the specific value of 67±3 obtained for Orion from CO data. An isotopic ratio as low as 43, as previously suggested based on optical absorption measurements of the local interstellar medium, is excluded by the C II data at about the 2σ level.

Carbon fractionation in photo-dissociation regions

“…They report line ratios between 36 and 122 with the highest optical depths τ = 3.3 +1.1 −0.8 belonging to the lowest line ratio of 36 ± 9 and low optical depths where ratios are high. Boreiko & Betz (1996) derive an intensity ratio of 46 in M42, consistent with an intrinsic ER of 58 +6 −5 and an optical depth of [CII] of 1.3. For a given χ, the IR drops with decreasing density and increasing mass.…”

HERSCHEL/HIFI SPECTRAL MAPPING OF C+, CH+, AND CH IN ORION BN/KL: THE PREVAILING ROLE OF ULTRAVIOLET IRRADIATION IN CH+ FORMATION

“…However, these would yield abundance ratios that are a factor of 2-3 lower than the total ratio of 67 based on local O observations in Orion by Langer & Penzias (1990. Boreiko & Betz (1996) derived τ 12 =1.2 toward θ 1 OriC, based on a kinetic temperature T kin =185±15 K calculated from OI and CII observations along that sightline. If we set τ 12 =1.2 as an average over our mapped region around KL, then we obtain an abundance ratio R=53 for the diffuse medium outside the Hot Core.…”

“…In order to estimate τ 12 , we recognize that the 12 C + / 13 C + integrated intensity ratio reflects the 12 C/ 13 C abundance ratio of the gas, provided that the 13 C + emission can be treated as optically thin. Following Boreiko & Betz (1996), the total isotopic abundance ratio R≡ 12 C/ 13 C is related to the ionic line intensity ratio I 13 /I 12 and τ 12 by…”

The nature of the [C ii] emission in dusty star-forming galaxies from the SPT survey

“…The two [CII] emission lines for 12 C and 13 C have been observed in local star forming regions, e.g. in M42 (Stacey et al 1991b;Boreiko & Betz 1996), NGC2024 (in the Orion nebula; Graf et al 2012), the Orion Bar, Mon R2, NGC 3603, the Carina Nebula and NGC 7023 (Ossenkopf et al 2013). These observations find optical depths ranging from τ ∼ 1 to τ ∼ 3, with on average a moderate optical dept τ ∼ 1.4.…”