Are infrared dark clouds really quiescent? | Astronomy & Astrophysics (A&A)

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Table 7

Optical depth τ and T_ex derived for CO (1 → 0) isotopologues, according to Eqs. (B.1) and (B.3)–(B.6).

Line	G28.34 S		IRDC 18530		IRDC 18306		IRDC 18308

	τ	T_ex (K)	τ	T_ex (K)	τ	T_ex (K)	τ	T_ex (K)
C¹⁸O (2 → 1) ^a	0.25	14	–	–	0.65	8	–	–
¹³CO (2 → 1) ^a	2.6	11	–	–	5.8	8	0.9	13
¹³CO (2 → 1) ^b	2.8	11	2.9	9	6.2	7	2.2	11

Notes.

^(a)

Derived from C¹⁷O (2 → 1), which is assumed to be optically thin.

^(b)

Derived from C¹⁸O (2 → 1), which is assumed to be optically thin.

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