Time evolution of the ²⁸SiO v = 1 J = 1–0 (left) and ²⁸SiO v = 2 J = 1–0 (right) lines observed in RX Boo during our August–September 2017 observing run. In both cases, the average spectrum of the complete run is plotted in black and the individual (one per day) spectra are plotted in red. The dashed vertical lines indicate the spectral components, selected by eye (Sect. 3.1), for which our statistical analysis is performed.