First detection of the Methylidyne cation (CH+) fundamental rotational
  line with the Herschel/SPIRE FTS
  Aims. To follow the species chemistry arising in diverse sources of the
Galaxy with Herschel. Methods. SPIRE FTS sparse sampled maps of the Orion bar &
compact HII regions G29.96-0.02 and G32.80+0.19 have been analyzed. Results.
Beyond the wealth of atomic and molecular lines detected in the high-resolution
spectra obtained with the FTS of SPIRE in the Orion Bar, one emission line is
found to lie at the position of the fundamental rotational transition of CH+ as
measured precisely in the laboratory (Pearson & Drouion 2006). This coincidence
suggests that it is the first detection of the fundamental rotational
transition of CH+. This claim is strengthened by the observation of the lambda
doublet transitions arising from its relative, CH, which are also observed in
the same spectrum. The broad spectral coverage of the SPIRE FTS allows for the
simultaneous measurement of these closely related chemically species, under the
same observing conditions. The importance of these lines are discussed and a
comparison with results obtained from models of the Photon Dominated Region
(PDR) of Orion are presented. The CH+ line also appears in absorption in the
spectra of the two galactic compact HII regions G29.96-0.02 and G32.80+0.19,
which is likely due to the presence of CH+ in the the Cold Neutral Medium of
the galactic plane. These detections will shed light on the formation processes
and on the existence of CH+, which are still outstanding questions in
astrophysics.
