Line profiles from observations and from synthesis. The number is φ_v of that panel. Column 1 from the left: time series of an average of 10–20 unblended CO Δv = 3 lines, using FTS spectra of χ Cyg, taken from Lebzelter et al. (2001). Observed heliocentric velocities were converted to systemic velocities RV* using heliocentric centre of mass radial velocity CMRV = − 7.5 km s^-1 from Hinkle et al. (1982). Column 2 and 3: synthetic CO Δv = 3 (5–2 P30) line profiles, from a model with Δφ_tot = 0.2, over a full cycle, shown for resolution 300 000 (Col. 2) and 70 000 (Col. 3). Column 4 and 5: synthetic CO Δv = 3 (5–2 P30) line profiles, from the original model, over a full cycle, shown for resolution 300 000 (Col. 4) and 70 000 (Col. 5).