Comparison of the ¹²CO (black line) and ¹³CO (pink line) (3−2) emission profiles obtained in the SiO peak (upper panel) and knot (lower panel) positions. The ratio of main-beam temperatures is also shown in the form of red dots (for the channels where the ¹³CO detection is over 3σ), orange dots (for the channels where the ¹³CO detection is between 2 and 3σ), and grey dots (for the remaining channels). Associated with this distribution are the grey horizontal dotted lines, which show values of 20 and 40 for this ratio.