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

C. Bhatt (Univ. of Western Ontario), J. Cami (Univ. of Western Ontario, SETI), E. Peeters (Univ. of Western Ontario, SETI), N. Clark (Univ. of Western Ontario), P.M. Baez (RIT), K. Volk (STScI), G.C. Sloan (STScI, UNC), J.H. Kastner (RIT), H.L. Dinerstein (Univ. of Texas), M. Matsuura (Cardiff Univ.), B. Balick (Univ. of Washington), K.E. Kraemer (Boston Coll.), K. Justtanont (Chalmers Univ. of Tech.), O. Jones (Royal Obs. Edinburgh), R. Sahai (JPL), and 20 others

2025, AAS journals, submitted

Planetary nebulae are the processing factories that turn previously ejected stellar material into complex molecules and dust grains, but the precise physical conditions and chemical routes that govern these processes are unclear. Especially the presence of abundant carbon-rich molecules in O-rich environments has posed challenges. Here we report the unambiguous detection of the methyl cation (CH₃⁺) in O-rich planetary nebula NGC 6302, using JWST MIRI/MRS observations. CH₃⁺, which is a key driver of organic chemistry in irradiated astrophysical environments, is detected for the first time in a planetary nebula. Here, we investigate the nature of the CH₃⁺ emission and its relation to other circumstellar components. We fit the observed CH₃⁺ emission with LTE models and derived the excitation temperature of 500-800 K everywhere it is seen, with column density in the first vibrationally excited state of the order of 10¹² cm². CH₃⁺-rich regions also exhibit bright emission by other molecular species such as ¹²CO, H₂, H I, HCO⁺, and polycyclic aromatic hydrocarbons (PAHs). This detection underscores the need to include molecular ions such as CH₃⁺ in planetary nebulae chemical models. Further observations, especially in the near-IR, are key to unravelling the different steps in this chemistry.

Home Library

Last modified 27 June, 2025. © Gregory C. Sloan and others.