CH+ towards the Orion Bar as seen by Herschel HIFI
V. Ossenkopf (I. Physikalisches Institut Universitaet zu Koeln), F.F.S. van der Tak (SRON), M. Rollig (I. Physikalisches Institut Universitaet zu Koeln), E. Bergin (University of Michigan), Y. Choi (Kapteyn Astronomical Institute & SRON) & the HEXOS team
The interaction between young massive stars and the ISM is one of the key questions of star formation. Photon dominated regions (PDRs) make excellent laboratories to investigate this question. The Orion Bar is a classical PDR, located at a distance of 400 pc. It is a target of the HEXOS (PI: E. Bergin) key program for the HIFI instrument onboard the Herschel Space Observatory.We investigate the formation of CH+ by comparing the observed line parameters to those observed for the C+, C and CO lines as well as to PDR models.The most probable reaction to form CH+ is the highly endothermic reaction: C+ + H2 → CH+ + H. To overcome the activation barrier, a couple of scenarios have been suggested, including turbulent dissipation and H2 vibrational excitation. Our preliminary analysis suggests, that turbulent dissipation can be excluded in the Orion Bar based on the observed narrow line widths. To test the H2 vibrational excitation we compare our results with corresponding maps of hot H2.