From core to envelope: revealing the deep dynamics of stars with two convective zones

TL;DR

This study simulates the internal structure of F-type stars with two convective zones, revealing how core dynamics influence gravity modes and their potential detectability via space photometry.

Contribution

First simulation of the global structure of F-type stars with detailed core, radiative interior, and envelope interactions affecting gravity mode spectra.

Findings

Core strongly influences excited g mode spectrum.

High-degree low-order modes are suppressed by core convection.

Modes maintain integrity up to the convective envelope, aiding detection.

Abstract

On the Hertzsprung-Russell diagram, F-type solar pulsators connect the Sun to intermediate mass stars located on the instability strip. With respect to lower mass stars, they are structurally peculiar in the sense that they are constituted of three distinct dynamical layers: a small convective core, a deep radiative interior, and a shallow convective envelope. Current asteroseismic techniques only provide limited information on the interior dynamics of these stars. Indeed only gravity modes (g modes), for which unambiguous characterisation is lacking, are able to probe the deep stellar layers. A better understanding of the excitation and behaviour in F-type solar pulsators is therefore necessary in order to consider their detection. In this work, we simulate for the first time the global stellar structure of an F-type star (core, radiative interior, envelope). We show that the contribution of the core strongly affects the spectrum of excited g modes, with low-order high-degree modes unable to form due to their interaction with the turbulent convection of the core. Finally, by computing the disc-integrated signature of the modes, we are able to demonstrate that they preserve their integrity up to the top of the convective envelope, which is a strong argument in favour of their detectability with spaceborne photometry.