Models of stars rotating near the critical limit

TL;DR

This paper discusses models of rapidly rotating stars near their critical velocity, highlighting the importance of accurately estimating the critical velocity, which varies depending on the star's Eddington factor, affecting observable features.

Contribution

It clarifies the existence of two different critical velocities for rotating stars and emphasizes the need for proper estimation to understand stellar deformation and related phenomena.

Findings

Two types of critical velocities depend on the Eddington factor.

Features at the two critical limits differ significantly.

Proper critical velocity estimation is crucial for interpreting observations.

Abstract

When the surface angular velocity is above about 70% of the critical angular velocity, many interesting features appear which may be tested by interferometric observations, like significant deformation of stars, variation of the effective temperature with the latitude. Also polar winds become important and equatorial disks may appear. Near the critical limit, convection is also favored in the outer layers. In the present paper, we emphasize the need for a proper estimate of the critical velocity since this is the ratio of the actual velocity of the star to that critical velocity which determines the amplitude of the above effects. We recall the existence of two critical velocities. The first one, also called the classical critical velocity is the one to consider when the star has an Eddington factor inferior to 0.639, while the second one is the one to be considered when the Eddington factor is above 0.639. The features of the star at these two critical limits may be very different.