Time evolution of optical and near-infrared spectral energy distribution of SSS17a compared with three models. The observational data are taken from Utsumi et al. (2017). All of the three models assume the same ejecta mass (0.03 M_⊙) and the same average velocity (〈v〉 = 0.1c). Orange curves show the model of the dynamical ejecta (Y_e = 0.10–0.40) while blue and green curves show the models with the elemental abundances calculated with high Y_e (Y_e = 0.30) and medium Y_e (Y_e = 0.25), respectively.