Séminaire POEMS sur les "ondes dans les étoiles"
14h00: Stéphane Mathis "Ondes de basses fréquences dans les étoiles"
Stellar interiors are the seat of low-frequency internal waves, which are driven by the Archimedean force, the Coriolis acceleration and the magnetic tension force, and acoustic waves. The complete set of these waves are very important since they provide key informations on the internal structure, dynamics and magnetism of stellar interiors. Moreover, they are also able to interact with mean flows, meaning that they modify the « general circulation » in stars, and thus their rotational evolution and mixing leading to a modification of their evolution with broad consequences. In this seminar, I will thus provide an overview of low-frequency waves in stellar interiors, of their excitation mechanisms, key examples of their interactions with other dynamical processes and of the state-of-the-art of their mathematical modeling.
14h35: Allan Sacha Brun "What's new inside the Sun?"
We will discuss our recent progress to model in 3-D the solar global interior dynamics using the anelastic spherical harmonic (ASH) code. We will show that the nonlinear mechanical and thermal coupling between a turbulent convective envelope and a stable radiative interior yields realistic rotation profile, with a differentially rotating convective envelope and a tachocline of shear at its base. We will further investigate the excitation and propagation of internal waves in the deep radiative interior. Thanks to the use of a realistic seismically calibrated stratification (i.e solar-like Brunt-V\"ais\"al\"a frequency), we observe a large spectrum of internal waves in our simulation. These modes are excited by the continuous pummeling of convective plumes. When comparing with asymptotic formulations and an adiabatic oscillation code we find a good overall agreement and confirm that those waves are indeed gravity waves. We then discuss their properties and visibility at the surface and compare with recent observations.