2017MNRAS.469.4649M

We present the results of a systematic stellar evolution study of binary mergers for blue supergiant (BSG) progenitors of Type II supernovae. In particular, these are the first evolutionary models that can simultaneously reproduce nearly all observational aspects of the progenitor of SN 1987A, Sk -69 °202, such as its position in the Hertzsprung-Russell diagram, the enrichment of helium and nitrogen in the triple-ring nebula and its lifetime before its explosion. The merger model, based on the one proposed by Podsiadlowski, Joss and Hsu, and Podsiadlowski, Morris and Ivanova, consists of a main-sequence secondary star that dissolves completely in the common envelope of the primary red supergiant at the end of their merger. We empirically explore a large initial parameter space - primary masses (15, 16 and 17 M_☉), secondary masses (2, 3,..., 8 M_☉) and different depths up to which the secondary penetrates the He core of the primary during the merger. The evolution of the merged star is continued until just before iron-core collapse, and the surface properties of the 84 pre-supernova models (of 16-23 M_☉) computed have been made available in this work. Within the parameter space studied, the majority of the models are compact, hot BSGs with effective temperature >12 kK and radii of 30-70 R_☉, of which six match the observational constraints of Sk -69 °202.