Modeling supernova emission at late times

We compare model calculations with observations of supernovae at late times to infer the time evolution of temperature, ionization and line emission. Here we mainly report on our results from our modeling of SN 1987A. We discuss the oxygen mass from the modeling of line fluxes. Line profiles show the distribution of the elements and the importance of including time dependence in the calculations. We discuss different approaches to determine the 44Ti-mass.