Line shapes of the CO dy = 2 line, for a grid of temperatures and densities, at 100 days. The black line is for the specified density and temperature in each panel. The gray line is for the lowest density and temperature and is used as a reference. The pink lines are observations from Hunter et al. (2009), plotted in panels where the model results are a good fit to the observations. In these simplified simulations we use n_CO = 10⁻³n_tot and n_e = 0.1n_tot.