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SAC Seminar - Mathieu Grosjean: Theoretical power spectra of solar-like oscillations in evolved low-mass stars

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Onsdag 15. oktober 2014,  kl. 15:15 - 16:00



CoRoT and Kepler observations of red giants reveal very rich spectra of non-radial solar- like oscillations allowing us to probe their internal structure.
The study of energetic aspects of these oscillations is of great importance to predict the peak parameters in the power spectrum.
The theoretical determination of lifetimes (or equivalently width) of the modes require non- adiabatic computations. Next, combined with a stochastic excitation model, we can also predict the height of the mode and finally obtain theoretical power spectra.
Comparison between our theoretical predictions with observations give important constraint on red-giants models. Lifetimes and amplitudes of modes trapped in the envelope (e.g. radial modes) constrain the characteristics of the convective envelope and its time-dependent interaction with oscillations. Lifetimes of mixed-modes (mainly dipolar modes) strongly depend on mode trapping, allowing us to probe the core of red-giants.
I will first discuss under which circumstances mixed modes are detectable for a large variety of red-giant stellar models, with emphasis on the effect of the evolutionary status of the star (along the red-giant branch and during the He-burning phase) on theoretical power spectra. Then I will present the first results of a detailed comparaison between theoretical and observed power spectra for a Kepler subgiant showing the validity of our theoretical computations and the additional constraints that the observations can bring to stellar and oscillations models.