Testing stellar evolution with asteroseismic inversions of a main sequence star harboring a small convective core

TL;DR

This study uses asteroseismic inversions of Kepler data to compare the internal structure of a main sequence star with predictions from stellar evolution models, revealing significant discrepancies near the convective core.

Contribution

It presents the first inverse analysis of a solar-type star with a small convective core, highlighting differences between observed and predicted internal structures.

Findings

Observed sound speed differs from model predictions near the core

Discrepancies are not explained by known physics like overshooting or diffusion

Highlights the need for improved stellar models

Abstract

The goal of stellar evolution theory is to predict the structure of stars throughout their lifetimes. Usually, these predictions can be assessed only indirectly, for example by comparing predicted and observed effective temperatures and luminosities. Thanks now to asteroseismology, which can reveal the internal structure of stars, it becomes possible to compare the predictions from stellar evolution theory to actual stellar structures. In this work, we present an inverse analysis of the oscillation data from the solar-type star KIC 6225718, which was observed by the \emph{Kepler} space observatory during its nominal mission. As its mass is about 20% greater than solar, this star is predicted to transport energy by convection in its nuclear-burning core. We find significant differences between the predicted and actual structure of the star in the radiative interior near to the convective core. In particular, the predicted sound speed is higher than observed in the deep interior of the star, and too low at a fractional radius of 0.25 and beyond. The cause of these discrepancies is unknown, and is not remedied by known physics in the form of convective overshooting or elemental diffusion.