Energetic study of solar-like oscillations in red giants

Observations of solar-like oscillations by CoRoT and Kepler space-borne telescopes, have opened new opportunities for the energetic modelling of these oscillations. In particular, oscillations propagating in both the convective envelope and the radiative core of evolved low-mass stars, called mixed-modes, have been detected, allowing us to investigate various physical processes acting on oscillations in these two regions. Theoretical predictions for the linewidths and the amplitudes of solar-like oscillations, as obtained and discussed in this thesis, strongly depend on the treatment of the interaction between convection and oscillations. Observed properties of solar-like oscillations thus gives us the opportunity to test and constrain this treatment.
The comparisons between observed and theoretical linewidths of main-sequence stars allow us to constrain the parameters of the time-dependent treatment of convection and to produce more accurate results. The remaining discrepancies will give us new clues for the improvement of the treatment of the interaction between convection and oscillations.
The modelling of the energetic aspects of solar-like oscillations in red giants allows us to derive a detectability limit for mixed-modes. These results are in overall good agreement with typical red-giant observed power spectra.
A detailed comparison between an observed subgiant and the corresponding theoretical predic- tions confirms that the main aspects of the observed energetic properties of solar-like oscillations are well reproduced by the theoretical modelling. Discrepancies between observed and theoret- ical linewidths of quadrupole mixed-modes lead us to invoke the existence of a new damping mechanism in the core of this star.