Comparison of the evolution of the main observables of SN 2009dd with the best-fit models computed with the general-relativistic, radiation-hydrodynamics code (total energy ~ 0.2 foe, initial radius 5 × 10¹³ cm, envelope mass 8 M_⊙). Top, middle, and bottom panels show the quasi-bolometric light curve, the photospheric velocity (the blue dashed line refers to the model plus an additive constant to match the data), and the photospheric temperature as a function of time. To estimate the photospheric velocity from observations, we used the value inferred from the Fe ii lines (see text for further details). The x −axes refer to days since explosion.