Observed transitions of CH₃OCH₃ (in black). The best-fit model is superposed in red (corresponding to the LTE modelling of both CH₃OCH₃ and CH₃OCHO explained in Sect. 5), and the corresponding spectroscopic parameters are listed in Table A.1. The transition at 257.911 GHz overlaps with a CH₃OCHO transition whose best-fit model (based on the many lines detected in our observations) is shown in blue. The grey shaded area corresponds to the filled histogram above and below the baseline.