Top: Si III 4552 line profiles obtained on JD 2 451 653 over a timespan of 3.9 h (orbital phases 0.890–0.927), showing the emergence of the quasi-centrally-located dip in the profile of m₁. The profile of m₂ is located at approximately +325 km s^-1, and displays the gradual appearance of a “blue spike”. Time increases from bottom to top. Bottom: sequence of profiles obtained on 2 451 655 over a timespan of 7.5 h (orbital phases 0.338–0.416). In this case, the line due to m₂ is initially at around −25 km s^-1 and marches blueward over the course of the night, appearing near the continuum in the very extended blue wing of m₁ by the end of the night.