The first two-dimensional stellar structure and evolution models of rotating stars

TL;DR

This paper introduces the first two-dimensional stellar evolution models for rotating stars, successfully matching observations and revealing new insights into stellar dynamics and chemical transport.

Contribution

It presents a novel 2-D time-evolving stellar model that incorporates rotation and chemical mixing, advancing beyond traditional 1-D models.

Findings

Model reproduces observed properties of a specific $eta$ Cephei star.

Meridional circulation has minimal impact on chemical transport.

Nuclear evolution outpaces angular momentum redistribution in late main sequence.

Abstract

Rotation is a key ingredient in the theory of stellar structure and evolution. Until now, stellar evolution codes operate in a 1-D framework for which the validity domain in regards to the rotation rate is not well understood. This letter aims at presenting the first results of self-consistent stellar models in two spatial dimensions that compute the time evolution of a star and its rotation rate along the main sequence together with a comparison to observations. We make use of an extended version of the ESTER code that solves the stellar structure of a rotating star in two dimensions with time evolution, including chemical evolution, and an implementation of rotational mixing. We have computed evolution tracks for a 12Msun model, once for an initial rotation rate equal to 15% of the critical frequency, and once for 50%. We first show that our model initially rotating at 15% of the critical frequency is able to reproduce all the observations of the $\beta$ Cephei star HD 192575 recently studied by Burssens et al. with asteroseismology. Beyond the classical surface parameters like effective temperature or luminosity, our model also reproduces the core mass along with the rotation rate of the core and envelope at the estimated age of the star. This particular model also shows that the meridional circulation has a negligible influence on the transport of chemical elements, like nitrogen, for which the abundance may be increased at the stellar surface. Furthermore, it shows that in the late main sequence, nuclear evolution is faster than the relaxation time needed to reach a steady state of the star angular momentum distribution. We have demonstrated that we have successfully taken the new step towards 2-D evolutionary modelling of rotating stars. It opens new perspectives on the understanding of the dynamics of fast rotating stars and on the way rotation impacts stellar evolution.