Influence of structural discontinuities present in the core of red-giant stars on the observed mixed-mode pattern and characterization of their properties

TL;DR

This study investigates how structural discontinuities in the cores of red-giant stars affect their mixed-mode oscillation patterns, using high-precision Kepler data to identify and characterize these core features.

Contribution

It provides the first detailed analysis of the impact of core structural discontinuities on mixed-mode patterns in red giants, linking observed deviations to core features.

Findings

Discovered deviations in mixed-mode frequencies indicative of core discontinuities.

Fitted these deviations to infer properties of the inner convective core.

Demonstrated the influence of core features on seismic signals.

Abstract

The space-borne missions CoRoT and Kepler have provided seismic data of unprecedented quality. Among the observed stars, red giants show a complex oscillation pattern exhibiting pressure modes as well as mixed modes. The latter carry information on the radiative region properties of these stars. The very high precision of Kepler data provide enough accuracy to decipher the complex structure of the mixed-mode pattern and, therefore, deduce precise information on the structure of the stellar core. In this work, we studied the precise influence of the core structural discontinuities on the mixed-mode pattern. These phenomena have indeed an influence on the gravity waves that propagate inside the core of the star and, therefore, on the mixed-mode pattern. In this study, we aim to investigate the impact of core structural discontinuities on the observed mixed-mode pattern and measure their properties for several red giants. We identified several objects showing evidence of deviations in their mixed-mode frequency pattern that are characteristic of core structural discontinuities. We fitted these deviations and showed that they likely correspond to the influence of the inner convective core of these stars.