2019ApJ...886...27W

We present the evolution of massive star progenitors of supernovae of type IIP. We take the example of the nearby and well-studied SN 2013ej. We explore how convective overshoot affects the stellar structure, surface abundances, and effective temperature of massive stars, using the Modules for Experiments in Stellar Astrophysics. In particular, models with moderate overshoot (f = 0.02-0.031) show the presence of blue loops in the Hertzsprung-Russell diagram with a red to blue excursion (log₁₀[T_eff/K] from <3.6 to >4.0) and transition back to red, during the core helium-burning phase. Models with overshoot outside this range of f values kept the star in the red supergiant state throughout the post-helium-ignition phases. The surface CNO abundance shows enrichment post-main-sequence and again around the time when helium is exhausted in the core. These evolutionary changes in surface CNO abundance are indistinguishable in the currently available observations due to large observational uncertainties. However, these observations may distinguish between the ratio of surface nitrogen to oxygen at different evolutionary stages of the star. We also compare the effects of convective overshoot on various parameters related to likelihood of explosion of a star as opposed to collapse to a black hole. These parameters are the compactness parameter, M₄, and µ₄. The combination µ₄ x M₄, and µ₄ have similar variations with f and both peak at f = 0.032. We find that all of our 13 M_☉ models are likely to explode.