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Étude de l'interaction convection-pulsations et application aux Céphéides

Abstract : Cepheid variables are pulsating giant stars that oscillate on radial acoustic modes. Their oscillations are sustained by a mechanism linked to the opacity in ionisation regions, the kappa-mechanism. This instability leads to the so-called 'Classical Instability Strip' in the Hertzsprung-Russel diagram. The coldest Cepheids, which are located close to the red edge of this instability strip, have an extended surface convective zone, in which a strong coupling between convection and oscillations may occur. This effect is by now represented by time-dependent convection models that involve many free unconstrained parameters. The purpose of this thesis is precisely to address this convection-pulsation coupling thanks to nonlinear simulations. Firstly, a linear-stability analysis has given us the most appropriate initial conditions to get unstable modes excited by kappa-mechanism. These favourable situations were then used as starting setups of nonlinear direct numerical simulations (DNS) computed thanks to an implicit solver of our own. We have thus performed the first 2-D simulations of the convection-pulsation coupling, in which the oscillations are sustained by kappa-mechanism. We have shown that the convective motions could possibly quench the oscillations. This result confirms the hypothesis that the stabilisation of coldest Cepheids, close to the red edge, is due to their surface convective zone
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Submitted on : Wednesday, December 9, 2009 - 9:50:47 AM
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  • HAL Id : tel-00439968, version 1

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Thomas Gastine. Étude de l'interaction convection-pulsations et application aux Céphéides. Astrophysique [astro-ph]. Université Paul Sabatier - Toulouse III, 2009. Français. ⟨tel-00439968⟩

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