Applications of an improved Monte Carlo code to the synthesis of early-time Supernova spectra

A Monte Carlo code developed originally for stellar winds and subsequently modified to compute synthetic spectra for the photospheric phases of supern ovae adopted the simplifying assumption of line formation by coherent scatt ering in the matter frame. In an improved code (Lucy 1999a), the Line absor ption of a packet of radiant energy is followed as before by the emission o f an identical amount of energy in the matter frame but now the frequency o f the packet's photons is chosen so that, statistically, the branching into the available permitted downward transitions is correctly represented. Thi s inclusion of branching is of some importance for supernova spectra, as em phasized in the light curve studies of Pinto & Eastman (2000). An improved line list is also adopted in the new code, and the emergent spectrum is com puted using the formal integral. Examples of synthetic spectra computed wit h this new code for supernovae of types Ia and II are presented and the imp rovements introduced by the incorporation of branching are discussed. Previ ous results obtained with a pure scattering code are shown not to be invali dated. Possible further code developments to achieve a fully NLTE Monte Car lo code are briefly described.