Research

Context:
One of the groundbreaking results of asteroseismology has been the detection of solar-like non-radial oscillations in red giant stars. On the one hand, these observations have paved the way for detailed studies of the internal structure of giant stars, providing unique and revolutionary tests of current models of stellar evolution. On the other hand, the development of large spectroscopic surveys provides detailed and precise chemical properties of stars.

Results:
I studied one of the first samples of CoRoT giant stars for which spectroscopic observations were available. This pioneering work, combining spectroscopic and asteroseismic constraints, reveals the very good agreement between my models of stellar evolution and the chemical and seismic properties observed. It contributes to a finer understanding of stellar structure and evolution. Finally, in 2018, I took part in the interpretation of the abundances observed on the surface of giant stars belonging to the NGC6791 cluster observed by the APOGEE and Kepler spectroscopic survey; using my stellar evolution models including mixing. We were able to show that the spectroscopic observations added to the seismic constraints could be explained by stellar evolution models including thermohaline mixing on the red giant branch.

Context:
Asteroseismology has also been widely used to estimate stellar properties (e.g. stellar mass, radius, and distance), providing a fundamental contribution to the characterization of planet hosting stars (e.g. Huber et al. 2013; Johnson et al. 2014) and stellar populations (Miglio et al. 2013). Rotation and convective-core overshoot are two examples of a number of key processes that change all the outputs of stellar models, with a significant impact on asteroseismic observables (e.g. Eggenberger et al. 2010; Lagarde et al. 2012; Montalban et al. 2013; Bossini et al. 2015; Constantino et al. 2015). Consequently, transport processes can have a significant impact on the determination of planet and star masses.

Results:
In the context of the determination of stellar properties using asteroseismology, we study the influence of rotation and convective-core overshooting on the properties of red-giant stars. We used models in order to investigate the effects of these mechanisms on the asymptotic period spacing of gravity modes ( \Delta \Pi_{\ell=1} ) of red-giant stars that ignite He burning in degenerate conditions ( M\lesssim 2.0M_\odot). We also compare the predictions of these models with Kepler observations. For a given \Delta \nu , \Delta \Pi_{\ell=1} depends not only on the stellar mass, but also on mixing processes that can affect the structure of the core. We find that in the case of more evolved red-giant-branch (RGB) stars and regardless of the transport processes occurring in their interiors, the observed \Delta \Pi_{\ell=1} can provide information as to their stellar luminosity, within ~10-20%. In general, the trends of \Delta \Pi_{\ell=1} with respect to mass and metallicity that are observed in Kepler red-giant stars are well reproduced by the models.