Simulations with new k−ω model offer insights into massive star convection processes

Researchers at Yunnan Observatories of the Chinese Academy of Sciences simulated the evolution of massive stars with masses ranging from 50 to 150 solar masses during the nitrogen sequence Wolf-Rayet (WNL) star phase.

They employed a newly developed k−ω model to handle the convective overshooting processes within the stellar interior, offering a more precise understanding of this complex phenomenon in massive stars.

This study was published in The Astrophysical Journal.

At the boundary between the convective and radiative zones of stars, fluid retains inertia and overshoots the convective zone, thereby bringing elements from the convective zone into the radiative zone.

WNL stars typically form during core hydrogen burning, with their surfaces becoming enriched in nitrogen due to strong winds that strip away their outer envelopes.

The processes of convection and overshooting transport nucleosynthesis products to the outer layers, resulting in anomalous surface enrichment and altering the stars’ evolutionary paths. Therefore, studying WNL stars provides insights into the effects of convection and mass loss on stellar evolution.

The researchers compared the results from the k−ω model with those from the previously used exponential decay model for handling the overshooting zone.

They found that the k−ω model predicted a broader range of mass and lifetime evolution for WNL stars under the same initial conditions, such as mass and metallicity. Additionally, it lowered the model limit for WNL star formation, which was attributed to the k−ω model’s ability to expand the mixing zone of materials within the star.

Furthermore, the researchers considered the factor of rotation and found that rotation may play a crucial role in the formation of lower-mass and metal-poor WNL stars. This effect was more pronounced in the previous model.

By utilizing a new model for convective overshooting, this study provides fresh perspectives and more accurate results in revealing the evolutionary patterns of special stellar phases like the WNL stages.

Moreover, the differences in outcomes between the two convective overshooting models offer the researchers alternative options for inferring the initial evolutionary environments and distributions of observed samples.