Formation of WNL Stars in the MW and LMC Based on the k − ω Model

Abstract

We adopt a set of second-order differential equations (k − ω model) to handle core convective overshooting in massive stars, simulate the evolution of nitrogen sequence Wolf–Rayet (WNL) stars with different metallicities and initial masses, both rotating and nonrotating models, and compare the results with the classical overshooting model. The results indicate that, under the same initial conditions, the k − ω model generally produces larger convective cores and wider overshooting regions, thereby increasing the mass ranges and extending the lifetimes of WNL stars, as well as the likelihood of forming WNL stars. The masses and lifetimes of WNL stars both increase with higher metallicities and initial masses. Under higher-metallicity conditions, the two overshooting schemes significantly differ in their impacts on the lifetimes of WNL stars, but are insignificant in the mass ranges of the WNL stars. Rotation may drive the formation of WNL stars in low-mass, metal-poor counterparts, with this effect being more pronounced in the overshooting model. The surface nitrogen of metal-rich WNL stars formed during the main-sequence phase is likely primarily from the CN cycle, while it may come from both the CN and NO cycles for relatively metal-poor counterparts. Our model can effectively explain the distribution of WNL stars in the Milky Way, but appears to have inadequacies in explaining the WNL stars in the LMC.