Detection of vibrational emissions from the helium hydride ion (HeH${}^{+}$) in the planetary nebula NGC 7027

Abstract

We report the detection of emission in the v=1-0 P(1) (3.51629 micron) and P(2) (3.60776 micron) 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 (IRTF) on Maunakea. The confirm the discovery of HeH+ reported recently by Guesten et al. (2019), who used the GREAT instrument on the SOFIA airborne observatory to observe its pure rotational J=1-0 transition at 149.137 micron. 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 micron spectral region, have led to the detection of more than sixty spectral lines including nine rovibrational emissions from CH+. The latter are detected for the first time in an astronomical source.

arXiv comment49 pages, including 17 figures. Accepted for publication in ApJ

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• Panchromatic HST/WFC3 Imaging Studies of Young, Rapidly Evolving Planetary Nebulae. II. NGC 7027
• HI-to-H${}_2$ Transitions in Dust-Free Interstellar Gas
• Revisiting the Formation of HeH${}^{+}$ in the Planetary Nebula NGC 7027
• Energy-transfer Quantum Dynamics of HeH${}^{+}$ with He atoms: Rotationally Inelastic Cross Sections and Rate Coefficients
• Observations and analysis of CH${}^{+}$ vibrational emissions from the young, carbon-rich planetary nebula NGC 7027: a textbook example of chemical pumping
• Exploring the Possibility of Identifying Hydride and Hydroxyl Cations of Noble Gas Species in the Crab Nebula Filament
• Anomalous intensities in the infrared emission of CH${}^{+}$ explained by quantum nuclear motion and electric dipole calculations
• Rovibrational spectroscopy of the CH${}^{+}$-He and CH${}^{+}$-He${}_4$ complexes
• Fate and detectability of rare gas hydride ions in nova ejecta: A case study with nova templates
• Chemistry and ro-vibrational excitation of HeH${}^{+}$ in the Planetary Nebula NGC 7027
• Detection of CH${}^{+}$, CH and H${}_2$ molecules in the Young Planetary Nebula IC 4997
• Mass loss by atmospheric escape from extremely close-in planets
• Interrelations between Astrochemistry and Galactic Dynamics
• Infrared line emissions from atoms and atomic ions in NGC 7027: improved wavelength determinations for infrared metal lines and a probable detection of Zn${}^{5+}$