The vibrations of red giant stars
Stars can exchange matter with their surroundings by ejection of their surface layers. Combined with transport processes inside the stars, this affects the chemical evolution of the entire galaxy. Red giants have a particularly large effect. The objective of the SEISMOLOGY IN RGB (Asteroseismology to constrain physic of transport processes occurring in red giant stars) project was to utilise asteroseismology of red giant stars to test current theoretical predictions of their internal structure and evolution. The ultimate goal was to improve upon our physical description of hydrodynamic processes such as stellar rotation on the red giant branch. Asteroseismology is a powerful tool to investigate the interior of stars. The CoRoT and Kepler space missions have obtained asteroseismic data for many stars, which has allowed the detection and characterisation of solar-like oscillations in a large number of red giants. The detection of rich oscillation spectra (including non-radial oscillation modes) has paved the way for detailed studies of their internal structure. The project developed strong collaborations with researchers involved in spectroscopic and asteroseismic (CoRoT and Kepler) data analysis, to compare their data with stellar evolution models. The period spacing of g-modes (ΔΠ) provides information on the evolutionary status of red giants (red giant branch stars, or core He burning stars). Changes in ΔΠ could be explained by differences in the density profile and then in the Brunt-Väisälä frequency profile and by the presence of a convective core induced by helium burning. These results are useful for a wide range of applications in astrophysics, including the characterisation of planet-host stars. The core rotation rate of red giant stars measured by asteroseismology shows a significant disagreement with current predictions from stellar models. This implies an unexpected transport process occurring on the red giant branch. The project was also interested in investigating the impact of predictions from the stellar evolution models on our understanding of the formation and evolution of the Milky Way. It further sought to quantify how transport processes occurring in the stellar interior can change the chemical patterns observed at the surface of stellar populations.
Keywords
Red giant stars, astrophysics, transport processes, asteroseismology, stellar evolution
