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.