Probing core overshooting using subgiant asteroseismology
Convective cores are the fuel reservoir of stars that are more massive than about 1.2 Msun. Their size therefore has a substantial influence on stellar evolution. However, several physical processes that remain poorly understood by theory can extend those convective cores. Observations are therefore required to help constrain them. In this talk, I will speak about how we can use subgiant asteroseismology to indirectly constrain the main-sequence convective core extension. Indeed, subgiant stars exhibit mixed modes, whose dual nature as pressure and gravity modes allows us to probe the very core of the star. We therefore used the full Kepler data set to thoroughly model KIC10273246, using a method that we specifically tailored for subgiants. We obtained models that show a good statistical agreement with the observations, and found that adding overshooting significantly improves the quality of the seismic fit. We also found that having access to several g-dominated mixed modes provides a stronger constraint on the structure of the star, especially the Brunt-Väisälä frequency and the central density. This study paves the way of a more general study, which will include subgiants observed with Kepler and TESS. Moreover, it led us to the study of the impact of other processes, such as convection and nuclear reactions, on the determination of convective cores size by the stellar evolution codes.