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Thanks to the precision of Kepler observations, [3] were able to measure the linewidth and amplitude of individual modes (including mixed modes) in several subgiant power spectra. We perform a forward modelling of a Kepler subgiant based on surface properties and observed frequencies. Non-adiabatic computations including a time- dependent treatment of convection give the lifetimes of radial and non-radial modes. Next, combining the lifetimes and inertias with a stochastic excitation model gives the amplitudes of the modes. We can now directly compare theoretical and observed linewidths and amplitudes of mixed-modes to obtain new constraints on our theoretical models.

In the framework of the data base project SSI (Stellar Seismic Indicesb), we have developed and tested a new method aiming at optimizing the simultaneous measurement of both the seismic indices characterizing the oscillations (Δν, νmax) and the indices characterizing the granulation signature. Here, we describe this method which is intended to take advantage of the MLE (maximum likelihood estimate) algorithm combined with the parametrized representation of the red giants pulsation spectrum following the Universal Pattern [6]. We report its performances tested on Monte Carlo simulations.

Determining stellar characteristics such as the radius, mass or age is crucial and asteroseismology is currently the most promising tool to provide these results accurately. We extend the SOLA inversion technique to new global characteristics in addition to the mean density [2] and apply our methodology to the acoustic radius and an age indicator based on the sound speed derivative. The results from SOLA inversions are compared with estimates based on the small and large frequency separations for several test cases. We show that SOLA inversions yield more accurate results than other techniques which are more sensitive to surface effects.

The PLATO space mission is designed to detect telluric planets in the habitable zone of solar type stars, and simultaneously characterise the host star using ultra high precision photometry. The photometry will be performed on board using weighted masks. However, to reach the required precision, corrections will have to be performed by the ground segment and will rely on precise knowledge of the instrument PSF (Point Spread Function). We here propose to model the PSF using a microscanning method.

CoRoT and Kepler measurements reveal us that the amplitudes of solar-like oscillations detected in red giant stars scale from stars to stars in a characteristic way. This observed scaling relation is not yet fully understood but constitutes potentially a powerful diagnostic about mode physics. Quasi-adiabatic theoretical scaling relations in terms of mode amplitudes result in systematic and large differences with the measurements performed for red giant stars. The use of a non-adiabatic intensity-velocity relation derived from a non-adiabatic pulsation code significantly reduces the discrepancy with the CoRoT measurements. The origin of the remaining difference is still unknown. Departure from adiabatic eigenfunction is a very likely explanation that is investigated in the present work using a 3D hydrodynamical model of the surface layers of a representative red giant star.

CoRoT and Kepler observations of red giants reveal rich spectra of non-radial solar-like oscillations allowing to probe their internal structure. We compare the theoretical spectrum of two red giants in the same region of the HR diagram but in different evolutionary phases. We present here our first results on the inertia, lifetimes and amplitudes of the oscillations and discuss the differences between the two stars.

Thanks to the CoRoT and Kepler spacecrafts, scaling relations (linking seismic indices and global stellar parameters) are becoming the cornerstone of ensemble asteroseismology. Among them, the relation between the cut-off frequency and the frequency of the maximum in the power spectrum of solar-like pulsators as well as the relation between mode lifetime and the effective temperature remain poorly understood. However, a solid theoretical background is essential to assess the accuracy of those relations and subsequently of the derived stellar parameters. We will thus present recent advances on the understanding of the underlying mechanisms governing those relations and show that the physics of mode lifetime (thus of mode damping) plays a major role.