The synthetic line profiles presented here are the result of a series of models :

• - Woosley's (1988) calculation of the stellar explosion yield the luminosity, the density and the velocity structure of the expanding SN as a function of time (Woosley's model 10HM was used)

• - subsequent Monte Carlo simulations of the radiation transport in the expanding photosphere are based on the atmosphere structure given by the model above for a given time. The calculations take into account tens of thousands of lines and yield the line blanketed continuum flux and the temperature structure.

• - The previous two models specify the physical condition of the expanding shell. With a third model the NLTE populations of 10 H and 12 He levels are determined and the emergent hydrogen lines profiles are obtained. The method of solving the NLTE problem is described by Wessolowski et al. (1988) and references therein.