Rectified spectral intensity in the wings of the He I λ6678 line at positions for V_r = +312 km s⁻¹ (above) and for V_r = −291 km s⁻¹ (below, offset by −0.03 for clarity) plotted against phase for the main periodicity. The numerical symbols refer to the last integer unit in the HJD of observation for the 1987 January sequence.