Twists in the flow: revisiting convective mixing in rotating stellar models. I. Effect on the stellar structure

TL;DR

This study examines how incorporating rotation effects into mixing-length theory (R-MLT) influences the internal structure, convective mixing, and angular momentum transport in stellar models, revealing significant differences from standard models.

Contribution

It introduces and applies rotating mixing-length theory (R-MLT) in stellar models, highlighting its impact on convection and stellar structure compared to traditional non-rotating models.

Findings

R-MLT reduces convective velocity and mixing length in the stellar core.

It causes about 20% reduction in the extent of the convective overshooting region.

R-MLT alters the chemical gradient and angular momentum transport near the core-envelope boundary.

Abstract

Convection and rotation are both key processes in stellar evolution modelling. While standard mixing-length theory (MLT) provides a widely used modelling of convection, it neglects the effects of rotation on convective transport. We investigate how rotating mixing-length theory (R-MLT), which accounts for the influence of rotation on convection, affects the internal structure, convective mixing, and angular momentum transport in stellar models in comparison to the standard non-rotating MLT. Using the MESA stellar structure and evolution software, we model the main-sequence evolution of a 5 M$_{\odot}$ star, for three cases: non-rotating, rotating with standard MLT for modelling convection, and rotating with R-MLT in convection zones, with the initial rotation rate set to 20 percent of the critical (Keplerian) value at the surface for the rotating models. We find that R-MLT reduces both the convective velocity and mixing length in the stellar core, leading to a smaller convective diffusion coefficient and about 20 percent reduction in the extent of the convective overshooting region. While the overall size of the convective core remains nearly unchanged, R-MLT changes the resulting chemical gradient at the core-envelope boundary, shifting the peak of the Brunt-V\"ais\"al\"a frequency and modifying the angular momentum transport in that region. Including the effects of rotation in the treatment of convection through R-MLT introduces measurable structural and transport differences, underscoring the importance of incorporating rotation-convection coupling in models of stars.