Illustration of the origin of the flux in the unadulterated model. Top panel: observer’s frame luminosity contribution δL_λ,R (the grayscale is saturated at a third of the true maximum in order to reveal better the weaker emitting regions) versus wavelength and ejecta velocity. The two contributing shells shown at left correspond to the H-rich envelope and to the He core in the progenitor. Bottom panel: total luminosity as well as the fractional luminosity from each shell (some line identifications are also provided).