Velocity evolution of the absorption maxima of the Hα (red squares), Hß (yellow diamonds), He i 5876 Å (yellow upward triangles), He i 6678 Å (red downward triangles), He i 1.083 µm (green rightward triangles), He i 2.058 µm (blue leftward triangles), and Fen 5169 Å (black circles) lines for the standard model. The black crosses show the velocity evolution of the (Rosseland mean) continuum photosphere, whereas the horizontal lines mark the outer borders of the carbon–oxygen core (blue) and the inner and outer (green and yellow) helium envelope.