Detection of CH${}^{+}$, CH and H${}_2$ molecules in the Young Planetary Nebula IC 4997

Abstract

We have detected CH${}^{+}$ and CH molecular absorption lines from the young compact planetary nebula IC 4997 from high resolution optical spectra. A high-resolution infra-red (H and K bands) spectrum provides detection of H${}_2$ emission lines amongst many other lines. The H${}_2$ lines provide an excitation temperature of 2100 K which may result from UV fluorescence in the envelope or from shocks formed at the interface between an expanding outflow of ionized gas and the neutral envelope ejected when the star was on the AGB. It is suggested that the CH${}^{+}$ may result from the endothermic reaction C + H${}_2$ $\to$ CH${}^{+}$ + H. Intriguingly, CH${}^{+}$ and also CH show a higher expansion velocity than H${}_2$ emission suggesting they may be part of the post-shocked gas.

arXiv comment12 pages, 2 tables, 6 figures, accepted for publication in Publications of the Astronomical Society of the Pacific (PASP)

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Cited by in corpus (2)

• An episodically variable stellar wind in the planetary nebula IC\,4997
• FAST search for circumstellar atomic hydrogen--I: the young planetary nebula IC 4997