FORMATION OF CH$^{+}$: SHOCK CHEMISTRY IN NGC 7027

Abstract

The formation of CH$^{+}$ in the interstellar medium has been an enigma for the past 70 years. Emission from the species is found in diffuse material, even though the major pathway leading to the species, C$^{+}$ + H${_2}$, is endothermic by 0.40 eV. The barrier for this reaction can be greatly reduced if the H${_2}$ is vibrationally excited. Using the Heterodyne Instrument for the Far Infrared (HIFI) on board the Herschel Space Observatory, we have mapped CH$^{+}$ $(J=1 \rightarrow 0)$, CH$^{+}$ $(J=2 \rightarrow 1)$, and C$^{+}$ $(J=3/2 \rightarrow 1/2)$ across the face of the young planetary nebula, NGC 7027. Analysis of the spectra has shown that CH$^{+}$, C$^{+}$, and vibrationally excited H${_2}$ apparently trace the same outflow in NGC 7027. Therefore CH$^{+}$ in this nebula likely forms from the activated C$^{+}$ + H${_2}$ reaction. Spectral maps, temperatures, and abundances of CH$^{+}$ will be presented along with spectral maps of C$^{+}$.