Detection of Vibrational Emissions from the Helium Hydride Ion (HeH<sup>+</sup>) in the Planetary Nebula NGC 7027
David A. Neufeld, Miwa Goto, T. R. Geballe, R. Güsten, K. M. Menten, H. Wiesemeyer
Abstract
Abstract We report the detection of emission in the v = 1 − 0 P (1) (3.51629 μ m) and P (2) (3.60776 μ m) rovibrational lines of the helium hydride cation (HeH + ) from the planetary nebula NGC 7027. These detections were obtained with the iSHELL spectrograph on NASA’s Infrared Telescope Facility on Maunakea. They confirm the discovery of HeH + reported recently by Güsten et al., who used the GREAT instrument on the SOFIA airborne observatory to observe its pure rotational J = 1 − 0 transition at 149.137 μ m. The flux measured for the HeH + v = 1 − 0 P (1) line is in good agreement with our model for the formation, destruction, and excitation of HeH + in NGC 7027. The measured strength of the J = 1 − 0 pure rotational line, however, exceeds the model prediction significantly, as does that of the v = 1 − 0 P (2) line, by factors of 2.9 and 2.3 respectively. Possible causes of these discrepancies are discussed. Our observations of NGC 7027, covering the 3.26–3.93 μ m spectral region, have led to the detection of more than 60 spectral lines including nine rovibrational emissions from CH + . The latter are detected for the first time in an astronomical source.