Physics of rotation: problems and challenges

TL;DR

This paper reviews key issues in the physics of rotating stars, including shape, gravity darkening, critical velocities, mass loss, instabilities, and internal mixing, emphasizing recent findings on rotational mixing and binary interactions.

Contribution

It highlights recent advances in understanding rotational mixing, the role of shear in differential rotation, and the effects of binary interactions on stellar rotation and mixing processes.

Findings

Rotational mixing is confirmed with high-quality data.

Shear processes are crucial for internal transport in differentially rotating stars.

Binary interactions can enhance shear and mixing effects.

Abstract

We examine some debated points in current discussions about rotating stars: the shape, the gravity darkening, the critical velocities, the mass loss rates, the hydrodynamical instabilities, the internal mixing and N--enrichments. The study of rotational mixing requires high quality data and careful analysis. From recent studies where such conditions are fulfilled, rotational mixing is well confirmed. Magnetic coupling with stellar winds may produce an apparent contradiction, i.e. stars with a low rotation and a high N--enrichment. We point out that it rather confirms the large role of shears in differentially rotating stars for the transport processes. New models of interacting binaries also show how shears and mixing may be enhanced in close binaries which are either spun up or down by tidal interactions.