The dynamics of a fully radiative rapidly rotating star enclosed within a spherical box
Abstract
Context: Recent results from interferometry and asteroseismology require models of rapidly rotating stars that are more and more precise.
Aims: We describe the basic structure and the hydrodynamics of a fully radiative star as a preliminary step towards more realistic models of rotating stars.
Methods: We consider a solar mass of perfect gas enclosed in a spherical container. The gas is selfgravitating and rotating, and is the seat of nuclear heating, and heat diffusion is due to radiative diffusion with Kramers type opacities. Equations are solved numerically with spectral methods in two dimensions with a radial GaussLobatto grid and spherical harmonics.
Results: We computed the centrifugally flattened structure of such a star: the von Zeipel model, which says that the energy flux is proportional to the local effective gravity is tested. We show that it overestimates the ratio of the polar to the equatorial energy flux by almost a factor 2. We also determine the BruntVäisälä frequency distribution and show that outer equatorial regions in a radiative zone are convectively unstable when the rotation is fast enough. We compute the differential rotation and meridional circulation stemming from the baroclinicity of the star and show that, in such radiative zones, equatorial regions rotate faster than polar ones. The surface differential rotation is also shown to reach a universal profile when rotation is slow enough (less than 36% of the breakup one), as long as viscosity and Prandlt number remain small.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 August 2007
 DOI:
 10.1051/00046361:20077263
 Bibcode:
 2007A&A...470.1013E
 Keywords:

 hydrodynamics;
 stars: rotation