The progenitor star and its evolution.

Results from the study of SN 1987A are discussed, focusing on observational and theoretical constraints on models of the progenitor star before and during the explosion. It is found that evolutionary models of the progenitor star at explosion must have log luminosity/solar luminosity = 5.0 + or - 0.2, log T(eff) = 4.2 + or - 0.05, and envelope mass/solar mass between 3 and 12. In the envelope at explosion, the model requirements include N/C = 8.8 + or - 4 and N/O = 1.5 + or - 0.8. In addition, models of the progenitor should include an initial mass of about 17-20 solar masses and a ratio of blue to red He burning lifetimes of about 7-10. Several models are compared with these requirements, showing that the only models which meet the requirements are those of Saio et al. (1988).