Detection of CH3+ in the O-rich planetary nebula NGC 6302

Bhatt, Charmi, Cami, Jan, Peeters, Els, Clark, Nicholas, Moraga Baez, Paula, Volk, Kevin, Sloan, G. C., Kastner, Joel H., Dinerstein, Harriet L. and Matsuura, Mikako ORCID: https://orcid.org/0000-0002-5529-5593 2025. Detection of CH3+ in the O-rich planetary nebula NGC 6302. The Astrophysical Journal

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Abstract

Planetary nebulae are sites where ejected stellar material evolves into complex molecules, but the precise physical conditions and chemical routes that govern these processes are unclear. The presence of abundant carbon-rich molecules in O-rich environments poses particular challenges. Here we report the first detection of methyl cation (CH3+) in any planetary nebula, observed in the O-rich nebula NGC 6302 using JWST MIRI/MRS observations. CH3+ is a key driver of organic chemistry in UV-irradiated environments. Spatially resolved observations reveal that CH3+ is co-located with 12CO, H2, H II, HCO+, and Polycyclic aromatic hydrocarbons (PAHs). LTE modelling of the CH3+ emission yields excitation temperatures of 500-800K in the inner bubble and torus, rising to 1000-2000K in the outer bubble of NGC 6302, with column densities ranging from ~10^11 to 10^13 cm^-2. This detection demonstrates that hydrocarbon radical chemistry must be incorporated into planetary nebulae chemical models. Further near-IR observations are crucial to map different chemical networks operating in these environments.

Item Type:	Article
Status:	In Press
Schools:	Schools > Physics and Astronomy
Publisher:	American Astronomical Society
ISSN:	1538-4357
Date of First Compliant Deposit:	24 September 2025
Date of Acceptance:	16 September 2025
Last Modified:	24 Sep 2025 15:30
URI:	https://orca.cardiff.ac.uk/id/eprint/181315

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