Evidence of structural discontinuities in the inner core of red-giant stars

Red giants are late-stage stars that burn hydrogen in a shell and, after core helium ignition, enter the clump phase, a key feature in color-magnitude diagrams widely used for distance, extinction, density, and chemical evolution studies. Using Kepler asteroseismic data, we perform a detailed characterization of the deepest layers of clump stars. We find evidence for large core structural discontinuities in about 6.7% of stars in our sample, implying a radiative thermal stratification in the mixing region beyond the convective core boundary. These stars are otherwise similar to the remaining stars, suggesting that the formation of discontinuities may be intermittent.

Mathieu Vrard, Margarida S. Cunha, Diego Bossini, Pedro P. Avelino, Enrico Corsaro, Benoît Mosser