Predicted normalised Lyα line profiles for an expanding shell with v_exp = 300 km s^-1, b = 40 km s^-1, and with varying Hi column densities (left panel), and varying dust content (right panel). All line profiles are normalised around  ± 5900 km s^-1. Left: shown are models with log N_HI =  19.3 (blue dotted), 19.9 (red dotted), 20.2 (black), 20.8 (green dashed) cm^-2 comparable to those in Fig. 16 of Verhamme et al. (2006), plus models with lower column densities (log N_HI =  16., 18., 19. cm^-2, solid blue), and with higher lower column densities (log N_HI =  21.1, 21.4, 21.7 cm^-2, solid red). Right: shown are models with τ_a = 0. (black, top), 0.1 (blue dotted), 0.5 (red dashed), 1. (green dashed) comparable to those in Fig. 16 of Verhamme et al. (2006), plus models with higher optical depths (τ_a = 1.5, 2., 3. (solid blue), and 4. (solid black)).