Grids of Wolf–Rayet Stars Using MESA with the k − ω Model: From 25 to 120 M ⊙ at Z = 0.02

Abstract

Abstract To explore overshoot mixing and rotational mixing beyond the convective core during the core He-burning phase in massive stars, we computed a grid of stellar models, both rotating and nonrotating, with the k − ω model at Z = 0.02, covering a mass range of 25–120 M ⊙. The rotating models start with a rotation rate of v ini/v crit = 0.4 at the zero-age main sequence, and the evolution is computed until the end of the central carbon-burning phase. Models with the k − ω model provide larger convective cores and a broadening of the main-sequence width. The diffusive-overshoot models with f ov = 0.027 are, on average, closer to the k − ω models for massive stars at Z = 0.02, particularly for the stars with masses greater than 40 M ⊙. The final masses of the Wolf–Rayet (WR) stars range from 9.5–17.5 M ⊙ and 10–23 M ⊙ for the rotating and nonrotating models, respectively. In the rotating models, the C/N ratio decreases slowly below 0.1 outside the convective core, resulting in a flatter element transition region. In addition, the lifetimes of the WNC phase are 1–4 × 104 yr, which is about 1 order of magnitude longer than that in the nonrotating models. The masses of the WNC stars are dominated by internal mixing processes and the maximum masses of the He-burning convective cores during the core He-burning phase are in the range of 15–35 M ⊙. The expected WNC/WR ratios are 0.059 and 0.004 for the rotating and nonrotating models, respectively.