Discovery of Far-Infrared Pure Rotational Transitions of CH~+ in NGC 7027

摘要

We report the discovery of the rotational spectrum of CH~+ in the Infrared Space Observatory Long Wavelength Spectrometer (LWS) spectrum of the planetary nebula NGC 7027. The identification relies on a 1996 reanalysis of the LWS spectrum by Liu et al. and on new LWS data. The strong line at 179.62 μm (coinciding with the 2_121_01 transition of water vapor) and the lines at 119.90 and 90.03 m (reported as unidentified by Liu et al.), whose frequencies are in the harmonic relation 2 : 3:4, are shown to arise from the J = 21, 32, and 43 rotational transitions of CH~+.