Asteroseismic Inference of the Central Structure in a Subgiant Star

TL;DR

This paper extends asteroseismic inverse analysis to a subgiant star, revealing that its core structure aligns with stellar evolution predictions despite mode frequency differences.

Contribution

It applies asteroseismic inverse techniques to a subgiant star, expanding the method beyond Sun-like stars and providing insights into its core structure.

Findings

Core structure matches predictions despite frequency differences.

Inferences about the inert helium core and hydrogen shell.

Method successfully extended to subgiant stars.

Abstract

Asteroseismic measurements enable inferences of the underlying stellar structure, such as the density and the speed of sound at various points within the interior of the star. This provides an opportunity to test stellar evolution theory by assessing whether the predicted structure of a star agrees with the measured structure. Thus far, this kind of inverse analysis has only been applied to the Sun and three solar-like main-sequence stars. Here we extend the technique to stars on the subgiant branch, and apply it to one of the best-characterized subgiants of the Kepler mission, HR 7322. The observation of mixed oscillation modes in this star facilitates inferences of the conditions of its inert helium core, nuclear-burning hydrogen shell, and the deeper parts of its radiative envelope. We find that despite significant differences in the mode frequencies, the structure near to the center of this star does not differ significantly from the predicted structure.