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

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 - omega model at Z = 0.02, covering a mass range of 25-120 M-circle dot. 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 - omega 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 - omega models for massive stars at Z = 0.02, particularly for the stars with masses greater than 40 M-circle dot. The final masses of the Wolf-Rayet (WR) stars range from 9.5-17.5 M-circle dot and 10-23 M-circle dot 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 x 10(4) 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-circle dot. The expected WNC/WR ratios are 0.059 and 0.004 for the rotating and nonrotating models, respectively