Seminars : Documents

Gravity waves in stellar interiors: from dynamical effects to seismic probing potential
Charly Pinçon (STAR)

Gravity waves, or buoyancy waves, are well observed in the Earth’s atmosphere and oceans. Similarly, their presence is ubiquitous in stellar interiors. In low-mass stars, convective motions in the external envelope generate gravity waves that tunnel toward the underlying stably-stratified core in which they can propagate. The spectral characteristics of these waves depend on the properties of their propagation cavity and their observation is thus expected to provide precious seismic constraints on stellar cores. In turn, we know that these waves can interact with the medium and modify the global dynamics, although they are still neglected in current stellar evolution codes. Gravity waves therefore stand for both a dynamical actor and an information carrier. In the last decades, the advent of the space-borne missions CoRoT and Kepler provided exquisite seismic data for thousands of low-mass stars. Among other successes, the detection of gravity modes in red giant stars gave us an unprecedented insight on the inner regions of stars and deeply questioned our understanding of stellar evolution. In particular, several studies clearly showed that the current modeling of the internal rotation evolution is insufficient, leading to huge uncertainties in the description of transport processes (i.e., of angular momentum, heat, or chemical species), as well as in the observational estimates of stellar parameters (i.e., mass, radius, or age). In this talk, I will demonstrate that the dynamical influence of low-frequency internal gravity waves on the rotation of stars is a serious option to reconcile the theoretical predictions with the observations. Furthermore, I will show that the probing potential of gravity modes in red giant stars (or more exactly mixed modes, owing to their coupling with acoustic modes at surface) has not been fully exploited yet, and that a detailed seismic analysis of their spectrum can provide us with even more constraints on the internal properties of these stars.