Analysis of SiO and comparison with CO. Left: ratio R_T of SiO(5–4) to SiO(6–5) line emitted fluxes as a function of R for |v_z | < 8 km s⁻¹. Corresponding temperature values using the relation T[K] = 12.5∕(ln(R_T) + 0.74 are shown in red on the scale of the ordinate. The red dashed line indicates constant R_T of 0.64 (T ~ 42 K) for R ≤1′′ and a linear increase of R_T to 0.89 (T ~ 20 K) from 1′′ to 2′′. Center-left: Doppler velocity spectrum of the SiO(5–4) data for R <0.1′′. Center-right: R distribution of the SiO(5–4) (red) and ¹²CO(2–1) (black) emission averaged over position angle ω, measured in Jy arcsec⁻², and averaged over − 2 < v_z < 6 km s⁻¹ as shown by the arrow in the center-left panel. Right: R dependence of the ¹²CO(2–1)/¹³CO(2–1) ratio (black) and of the ²⁸SiO(5–4)/²⁹SiO(5–4) ratio (red).