Analysis of type IInSN1998S: Effects of circumstellar interaction on observed spectra

We present spectral analysis of early observations of the Type IIn supernov a 1998S using the general non-local thermodynamic equilibrium atmosphere co de PHOENIX. We model both the underlying supernova spectrum and the overlyi ng circumstellar interaction region and produce spectra in good agreement w ith observations. The early spectra are well fitted by lines produced prima rily in the circumstellar region itself, and later spectra are due primaril y to the supernova ejecta. Intermediate spectra are affected by both region s. A mass-loss rate of order (M) over dot similar to 0.0001-0.001 M. yr(-1) is inferred for a wind speed of 100-1000 km s(-1). We discuss how future s elf-consistent models will better clarify the underlying progenitor structu re.