The CoRoT target HD49933: a possible seismic signature of heavy elements ionization in the deep convective zone

TL;DR

This study uses seismic diagnostics to identify a signature of heavy element ionization in HD 49933, revealing insights into the star's deep convective zone and ionization processes.

Contribution

The paper introduces a novel seismic diagnostic sensitive to heavy element ionization, providing new insights into stellar interior processes.

Findings

Detected a seismic signature of heavy element ionization.

Located the ionization region between helium second ionization and the convective zone base.

Identified the ionization signature approximately 5% below the stellar surface.

Abstract

We use a seismic diagnostic, based on the derivative of the phase shift of the reflected by the surface acoustic waves, to probe the outer layers of the star HD 49933. This diagnostic is particularly sensitive to partial ionization processes occurring above the base of the convective zone. The regions of partial ionization of light elements, hydrogen and helium, have well known seismological signatures. In this work we detect a different seismic signature in the acoustic frequencies, that we showed to correspond to the location where the partial ionization of heavy elements occurs. The location of the corresponding acoustic glitch lies between the region of the second ionization of helium and the base of the convective zone, approximately 5% below the surface of the stars.