Model line profiles for a primary star with R₁ = 7.6 R_⊙ and for ω_per = 233°, illustrating the transition in shape from parabolic-like to “boxy” (i.e., having a flat-bottom and steep wings), the bottom of which then slopes upward towards the blue, until the parabolic-like shape is recovered. The sequence from periastron to apastron is shown on each of the left panels and from apastron to periastron on the right. Time increases upward. Note the symmetry, caused the by geometry of the tidal flows and the orbital motion. The two panels on the left correspond to ω_per = 233° and the two panels on the right to ω_per = 277°.