TESTING CONVECTIVE-CORE OVERSHOOTING USING PERIOD SPACINGS OF DIPOLE MODES IN RED GIANTS

Abstract

Uncertainties on central mixing in main sequence (MS) and core He-burning (He-B) phases affect key predictions of stellar evolution such as late evolutionary phases, chemical enrichment, ages etc. We propose a test of the extension of extra-mixing in two relevant evolutionary phases based on period spacing Delta_P of solar-like oscillating giants. From stellar models and their corresponding adiabatic frequencies (respectively computed with ATON and LOSC codes) we provide the first predictions of the observable Delta_P for stars in the red giant branch (RGB) and in the red clump (RC). We find: i) a clear correlation between Delta_P and the mass of the helium core (M_He); the latter in intermediate-mass stars depends on the MS overshooting, hence it can be used to set constraints on extra mixing during MS when coupled with chemical composition; ii) a linear dependence of the average value of the asymptotic period spacing (<Delta_P>_a) during the He-B phase on the size of the convective core. A first comparison with the inferred asymptotic period spacing for Kepler RC stars suggests the need for extra mixing also during this phase, as evinced from other observational facts.