Computed model profiles of the 30α (left) and 26α (right) transitions, excluding collisional broadening and radiative damping, are shown in black (truncated at a value of0.5, the peak value is 1.0). The blended profiles of the eight atoms and isotopes are shown in colours to illustrate their relative contributions and the mass-shifts in frequency. All of the profiles are slightly asymmetrical owing to the fine structure as described in Appendix C. A turbulent velocity Δυ_turb = 7.5 km s⁻¹ is adopted so that the fitted FWHMs of the model profiles match the observed width, 8.5 km s⁻¹.