Towards a unified model of stellar rotation

TL;DR

This paper compares various stellar rotation models using detailed evolution tracks to evaluate their ability to match observed stellar phenomena, aiming to develop a unified understanding of stellar rotation effects.

Contribution

It introduces a new stellar rotation code and systematically compares different models' predictions with observational data to identify the most accurate approaches.

Findings

Models with uniform specific angular momentum better reproduce nitrogen enrichment.

Solid-body rotation models more accurately match main sequence broadening.

Comparison highlights key differences in angular momentum transport assumptions.

Abstract

The effects of rapid rotation on stellar evolution can be profound. We are now beginning to gather enough data to allow a realistic comparison between different physical models. Two key tests for any theory of stellar rotation are first whether it can match observations of the enrichment of nitrogen, and potentially other elements, in clusters containing rapid rotators and secondly whether it can reproduce the observed broadening of the main sequence in the Hertzsprung-Russel diagram. Models of stellar rotation have been steadily increasing in number and complexity over the past two decades but the lack of data makes it difficult to determine whether such additions actually give a closer reflection of reality. One of the most poorly explored features of stellar rotation models is the treatment of angular momentum transport within convective zones. If we treat the core as having uniform specific angular momentum the angular momentum distribution in the star, for a given surface rotation, is dramatically different from what it is when we assume the star rotates as a solid body. The uniform specific angular momentum also generates strong shears which can drive additional transport of chemical elements close to the boundary of a convection zone. A comparison of different models and their reproduction of observable properties with otherwise identical input physics is essential to properly distinguish between them. We compare detailed grids of stellar evolution tracks of intermediate and high-mass stars produced using several models for rotation generated with our new stellar rotation code.