Non-LTE analysis of SiO emission lines. A series of RADEX models were run to estimate the kinetic temperature and density from the observed ratios of SiO J = 2−1 and J = 5−4 lines. Coloured dashed lines represent the ratio derived in the three regions highlighted in Fig. 1; the coloured shaded regions correspond to the error bars of the derived ratios, after assuming a 20% uncertainty on the peak brightness temperatures of each region. Solid curves represent the different temperatures obtained with the grid of models.