Formation of WNL stars for the MW and LMC based on the k-omega model

TL;DR

This study uses the $k-\omega$ model to simulate massive star evolution, revealing that it predicts larger convective cores and longer WNL star lifetimes, with implications for understanding their distribution in the Milky Way and LMC.

Contribution

The paper introduces the application of the $k-\omega$ model to simulate WNL star formation, highlighting differences from classical overshooting models and exploring effects of metallicity and rotation.

Findings

The $k-\omega$ model produces larger convective cores and longer WNL star lifetimes.

Higher metallicity and initial mass increase WNL star mass and lifetime.

Rotation influences WNL star formation, especially in low-mass, metal-poor stars.

Abstract

We adopt a set of second-order differential equations ($k-\omega$ model) to handle core convective overshooting in massive stars, simulate the evolution of WNL stars with different metallicities and initial masses, both rotating and non-rotating models, and compare the results with the classical overshooting model. The results indicate that under the same initial conditions, the $k-\omega$ 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 lifetimes of the WNL stars, but 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 OV model. The surface nitrogen of metal-rich WNL stars formed during the MS 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.