Position and velocity of the peak positions of the Gaussian-fitted components of the ²⁸SiO, ²⁹SiO J =  5−4, and ²⁸SiO, ³⁰SiO J =  6−5 ground-state vibrational emission lines of the mid-configuration dataset. The black circle in the middle represents the size of the stellar photosphere (Sect. 3). The marker size reflects the magnitude of the integrated flux of the Gaussian-fitted component, scaled as log₁₀(integrated flux). The dashed black line indicates the PA = 70° axis.