Potential CH₃O¹³CHO transitions at 246.78 GHz whose spectroscopic parameters are listed in Table A.1. The dashed lines correspond to the results of the best-fit Gaussian components obtained from the high spectral resolution methanol transitions at −2 km s⁻¹, 2.8 km s⁻¹ and 9.9 km s⁻¹ (Vastel et al. 2022). The red line corresponds to the modelled transitions as described in Sect. 5. The shaded area corresponds to the filled histogram above and below the baseline.