Table 4
Optical depth and abundance ratios for CO, 13CO, OCS, and CH3CN with respect to their rare isotopologues in each substructure of Orion KL.
| Species | ℜα | HC | mm2 | mm3a | mm3b | NE | S | OF1N | OF1S | |
| τCO (2 → 1) | 54 | 53 | 117 | 107 | 74 | 90 | 36 | 22 | ||
| NCOτ/ NC18O | 560 ± 25 | 1263.0± 21.8 | 1541.0± 57.1 | 2422.0± 46.6 | 2765.0± 72.3 | 3100.0± 52.9 | 2934.0± 18.8 | 2640.0± 33.7 | 1517.0± 29.8 | |
| NCO/ NC18O | ⋆ | 23.4± 0.4 | 29.1± 1.1 | 20.7± 0.4 | 25.8± 0.7 | 41.9± 0.7 | 32.6± 0.2 | 73.3± 0.9 | 68.9± 1.4 | |
|
1.1 | 0.25 | 2 | 1.5 | 2 | 1.5 | 0.02 | 0.08 | ||
| N13COτ/ NC18O | 7.2 ± 0.9 | 10.8± 0.2 | 7.3± 0.2 | 14.6± 0.2 | 13.1± 0.2 | 12.8± 0.0 | 10.6± 0.0 | 7.6± 0.0 | 9.7± 0.3 | |
| N13CO/ NC18O | ⋆ | 6.5± 0.1 | 6.5± 0.2 | 6.3± 0.1 | 6.8± 0.1 | 5.5± 0.0 | 5.5± 0.0 | 7.5± 0.0 | 9.3± 0.3 | |
| τ OCS (19 → 18) | 5.5 | 8.5 | 6 | 10 | ≤6 | ≤6 | ≤2 | – | ||
| NOCSτ/ NO13CS | 77 ± 7 | 79.7± 0.7 | 81.1± 2.0 | 80.1± 3.0 | 78.2± 0.0 | ≤ 195.2 | ≤ 121.3 | ≤ 101.1 | – | |
| NOCS/ NO13CS | ⋆ | 14.4± 0.1 | 9.5± 0.2 | 13.3± 0.5 | 7.8± 0.0 | ≥ 32.4 | ≥ 20.2 | ≥ 43.7 | – | |
| τ CH3CN (122 → 112) | 18 | 11 | 8.5 | 9 | 17 | ≤3.5 | ≤13 | ≤4 | ||
|
77 ± 7 | 79.6± 3.0 (76.6± 2.4)∗ | 77.7± 3.1 | 78.1± 1.9 | 79.8± 0.3 | 82.3± 6.7 | ≤ 168.3 | ≤ 176.3 | ≤ 130.0 | |
|
⋆ | 4.4± 0.2 (4.3± 0.1)∗ | 7.1± 0.3 | 9.2± 0.2 | 8.9± 0.0 | 4.8± 0.4 | ≥ 46.6 | ≥ 13.6 | ≥ 31.9 | |
Notes. The values are derived from the single strongest transition of each species using Eqs. (3) and (4). † or ⋆ mark the estimations with or without optical depth correction. “≥(≤)” come from the 3σ limit of the non-detection of O13CS (OCS) and 
. The ratios between isotopes ℜα of 12C /13C and 16O /18O are provided from the local ISM ratio measured in Wilson & Rood (1994). Uncertainties on the measured values are typically ≤10% (written as the subscript), as determined from Trot, partition function Q(Trot), and 
of the transition. “*" denotes the ratio temperature derived from .
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