Gravity darkening in late-type stars

Raphaël Raynaud (1, 2) , Michel Rieutord (3) , Ludovic Petitdemange (4) , T. Gastine (5) , Bertrand Putigny (3)

1 DAP - Département d'Astrophysique (ex SAP)
2 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
3 IRAP - Institut de recherche en astrophysique et planétologie
4 LERMA (UMR_8112) - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
5 IPGP - Institut de Physique du Globe de Paris

Recent interferometric data have been able to constrain the brightness distribution at the surface of nearby stars, in particular the gravity darkening that makes fast rotating stars brighter at their poles than at their equator. However, good models of gravity darkening are missing when the stars own a convective envelope. In order to better understand how rotation affects the heat transfer in stellar convective envelopes, we studied the heat flux distribution in latitude at the outer surface of numerical models of anelastic convection in rotating sphericall shells. We found that the variations of the surface brightness are mainly controlled by the surface value of the local Rossby number: when the Coriolis force dominates the dynamics, the heat flux is weakened in the equatorial region by the zonal wind and enhanced at the poles by convective motions inside the tangent cylinder. However, in presence of a strong background density stratification, as expected in real stars, the increase of the local Rossby number in the outer layers leads to the uniformisation of the surface heat flux distribution.

Mots clés: methods: numerical; convection; hydrodynamics; stars: interiors

Domaines: Astrophysique stellaire et solaire [astro-ph.SR]

Raphaël Raynaud, Michel Rieutord, Ludovic Petitdemange, T. Gastine, Bertrand Putigny. Gravity darkening in late-type stars. Journées de la SF2A, Jul 2018, Bordeaux, France. 2018. ⟨hal-02426744⟩