We present the results of a detailed , 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 ^ { \circ } 202 , such as its position in the HR 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 \citet pods1992a , pods2007 , 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 , such as primary masses ( 15 \mathrm { M } _ { \odot } , 16 \mathrm { M } _ { \odot } , and 17 \mathrm { M } _ { \odot } ) , secondary masses ( 2 \mathrm { M } _ { \odot } , 3 \mathrm { M } _ { \odot } , … , 8 \mathrm { M } _ { \odot } ) 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 ( 16 \mathrm { M } _ { \odot } -23 \mathrm { M } _ { \odot } ) computed have been made available in this work .
Within the parameter space studied , the majority of the pre-supernova models are compact , hot BSGs with effective temperature > 12 \mathrm { kK } and radii of 30 \mathrm { R } _ { \odot } -70 \mathrm { R } _ { \odot } of which six match nearly all the observational properties of Sk –69 ^ { \circ } 202 .