A Theoretical Study of Acoustic Glitches in Low-Mass Main-Sequence Stars

TL;DR

This paper provides a theoretical analysis of acoustic glitches in low-mass main-sequence stars, revealing how these features relate to stellar ionization zones and their potential as diagnostic tools.

Contribution

It identifies the specific acoustic signatures of helium ionization zones and their relation to stellar structure, enhancing the understanding of stellar oscillation diagnostics.

Findings

The helium ionization zone signature is linked to a peak in  between ionization zones.

The acoustic glitch due to helium ionization is most detectable in stars with 0.9-1.2 solar masses.

The study clarifies the relationship between acoustic glitches and stellar ionization features.

Abstract

There are regions in stars, such as ionization zones and the interface between radiative and convective regions, that cause a localized sharp variation in the sound speed. These are known as "acoustic glitches". Acoustic glitches leave their signatures on the oscillation frequencies of stars, and hence these signature can be used as diagnostics of these regions. In particular, the signature of these glitches can be used as diagnostics of the position of the second helium ionization zone and that of the base of the envelope convection zone. With the help of stellar models we study the properties of these acoustic glitches in main-sequence stars. We find that the acoustic glitch due to the helium ionization zone does not correspond to the dip in the adiabatic index \Gamma_1 caused by the ionization of HeII, but to the peak in \Gamma_1 between the HeI and HeII ionization zones. We find that it is easiest to study the acoustic glitch due to the helium ionization zone in stars with masses in the range 0.9--1.2 M_\odot.