observational periods can be found in Table 1. The 2021-2022 MUSE observations were executed as a filler programme, therefore the observing conditions were suboptimal. For some analyses, these conditions (lunar distance, lunar illumination, thick clouds, etc.) caused significant contamination to the cubes, which reduced signal-to-noise and influenced spectral slope. We do not include these observations in our analysis.
2.1. Data Reduction We reduced the raw datacubes using the standard ESO Reflex automated data reduction pipeline, defined in Freudling et al. (2013) and Weilbacher 7 et al.

(2020), and hereafter referred to as Reflex. Reflex’s main MUSE data products consist of reduced and calibrated datacubes, white-light images, and pixel tables. The datacubes are the reconstructed 3D (x,y,λ) MUSE spatio-spectral datacubes. The white light images are datacubes that were collapsed along the λ axis, which produced a 2D (x,y) image corresponding to the entire optical regime. The pixel tables are ancillary products that store the intermediate data about the reduction products, and are not used in this analysis. Across all datacubes, we utilised Reflex, standard star observations, and other standard calibrations to compute the line spread function, flux calibrations, instrument geometry corrections, illumination corrections, sky subtraction, and initial telluric absorption corrections. The sky subtraction was executed using dedicated sky observations that were reduced and calibrated in tandem with the main datacubes. However, residual sky lines remained in the dataset, but did not cause significant contamination to our sought chemical emission lines and bands, so we did not seek further corrections. The initial Reflex telluric corrections did not provide a satisfactory correction to our datacubes, and did significantly affect the CN A2Π–X2Σ+ (1,0) Red band, so we reran reductions without Reflex telluric corrections. We tried a more explicit telluric correction via the ESO Molecfit telluric correction software, outlined in Kausch et al. (2015) and Smette et al. (2015), hereafter referred to as Molecfit. We corrected for telluric contamination in each datacube via our novel method described more in subsection 2.2. We achieved a much higher quality telluric correction with this method, which resulted in as much as a 25× increase of CN gas signal in the redder wavelengths. We used this workflow to produce our primary set of science datacubes. To investigate the presence of forbidden oxygen [OI] emission in the coma, we reran the Reflex reductions without sky subtractions, performed Molecfit corrections, and forced Reflex to output a fourth data product: the reduced and calibrated sky observation datacubes. We used these sky observations to help isolate cometary [OI] emissions from atmospheric [OI] emissions. This method is necessary due to the high levels of noise introduced when Reflex subtracted the strong [OI] sky emissions. Therefore, we needed to perform our own more nuanced subtraction, first outlined in Opitom et al. (2020) and described further in subsection 3.3.1. This constituted our secondary science dataset, which preserved the cometary [OI] signal.