Pierre Demarque



    A poorly understood aspect of stellar physics is the role played by turbulent convection and overshooting into radiative layers. These uncertainties affect stellar lifetimes and internal mixing of chemical elements. In the case of cool stars with convective envelopes, the depth of the convection zone depends sensitively on the efficiency of convection in the atmospheric and subphotospheric layers. With the help of high performance computing (HPC) it is now possible to perform physically realistic three-dimensional numerical simulations of turbulence and its interaction with the radiation field (3D radiation hydrodynamics or 3D RHD) in stellar envelopes and atmospheres.

    One of the goals of this research is to introduce the parameterized results into 1D models of stellar interiors. Another is to understand the excitation of observed global non-radial oscillations, and to calculate the effects of surface structure on the oscillation frequencies (the so-called "surface term"). The effects on interior models and stellar evolution can be tested observationally using high precision traditional astronomical observations supplemented by the techniques of seismology.

    The results of the 3D RHD simulations can be similarly incorporated in stellar atmosphere models. Observational tests of the models include comparisons with both observed line strengths and line profiles, and with the continuous spectral energy distribution in stellar spectra, leading to better composition estimates and improved atmospheric dynamics.

    The tools of solar seismology (helioseismology) and stellar seismology (asteroseismology) provide powerful independent means of testing the theory of stellar structure and evolution. The structure of the deep interior is probed by studying the propagation of p-modes (or sound waves, which are excited by pressure perturbations) and g-modes (excited by buoyancy forces).

Historical note: stellar structure pioneer J. Homer LANE