CO⁺ is a typical PDR molecule particularly intense in the molecular cloud/HII interface region. The two strongest fine structure lines of the N = 2 – 1 transition as well as one fs component of the 3 – 2 transition were detected in the vicinity of the M17SW cloud by
W. B. Latter, C. K. Walker, and P. R. Maloney,
Detection of the Carbon Monoxide Ion (CO⁺) in the Interstellar Medium and a Planetary Nebula
Astrophys. J. 419, L97–L100 (1993).
The strongest 2 – 1 line was also detected toward the planetary nebula NGC 7027; this is a late type star phase after the AGB (asymptotic giant branch) phase.

The molecular cation has also been seen in the reflection nebula NGC 7023 which is in the vicinity of a Be star:
A. Fuente, J. Martin-Pintado,
Detection of CO⁺ toward the Reflection Nebula NGC 7023
Astrophys. J. 477, L107–L109 (1997).

C. Ceccarelli, E. Caux, M.Wolfire, A. Rudolph, B. Nisini, P. Saraceno, and G.J. White,
have reported on
ISO Detection of CO⁺ toward the protostar IRAS 16293–2422
Astron. Astrophys. 331, L17–L20 (1998)
in rather highly excited rotational states (N = 14 – 13 to 21 – 20). The authors attributed this to J-shocks.

Contributor(s): H. S. P. Müller; 05, 2009