Models of rotating massive stars: impacts of various prescriptions

TL;DR

This paper examines how different prescriptions for diffusion coefficients in rotating massive star models affect their evolutionary predictions, highlighting which prescriptions align best with observed surface abundance changes.

Contribution

It provides a comparative analysis of various diffusion coefficient prescriptions and their impact on stellar evolution models of rotating massive stars.

Findings

Surface velocity evolution is minimally affected by prescription choice.

Models with Maeder (1997) and Zahn (1992) coefficients best match observed surface abundances.

Most stellar evolution outputs show significant dependence on diffusion prescriptions.

Abstract

The rotation of stars has many interesting and important consequences for the photometric and chemical evolution of galaxies. Many of the predictions of models of stellar rotation are now compared with observations of surface abundances and velocities, with interferometric studies of fast rotating stars, with internal rotation profiles as they can be deduced by asteroseismology, to cite just a few observational constraints. In this paper, we investigate how the outputs of models depend on the prescriptions used for the diffusion coefficients included in the shellular rotating models. After recalling the various prescriptions found in the literature, we discuss their impacts on the evolutionary tracks and lifetimes of the Main-Sequence (MS) phase, the changes of the surface composition and velocities during the MS phase, the distribution of the core helium lifetime in the blue and the red part of the HR diagram, the extensions of the blue loops, the evolution of the angular momentum of the core, and the synthesis of primary nitrogen in fast-rotating metal-poor massive stars. While some of these outputs depend only slightly on the prescriptions used (for instance, the evolution of the surface velocities), most of them show a significant dependence. The models which best fit the changes of the surface abundances are those computed with the vertical shear diffusion coefficient of Maeder (1997) and the horizontal shear diffusion coefficient by Zahn (1992).