Spectral evolution for models rs10/v1e4/b0p4 (top left), rs10/v1e4/b0p8 (top right), rs10/v5e3/b0p04 (bottom left), and rs10/v2p5e3/b0p04 (bottom right). The main difference between these models is the impact parameter (0.4 or 0.8 R_⋆; top row) or the velocity of the collision (5000 or 2500 km s⁻¹; bottom row). For the last three models, the CMFGEN calculation is truncated at 5–10 d; convergence difficulties prevented the calculations from being carried out until the ejecta were fully optically thin (see Fig. 3).