Frequency dependence of Delta_nu of solar-like oscillators investigated: Influence of HeII ionization zone

TL;DR

This paper investigates how the large frequency separation in solar-like oscillators varies with frequency, focusing on the influence of the HeII ionization zone, and compares main-sequence and giant stars using evolutionary models.

Contribution

It provides a detailed analysis of the frequency dependence of Delta_nu in different stellar evolutionary stages, highlighting the role of the HeII ionization zone.

Findings

Frequency dependence of Delta_nu varies between main-sequence and giant stars.

HeII ionization zone significantly influences the frequency dependence of oscillation modes.

Main-sequence stars show more pronounced frequency dependence compared to giants.

Abstract

Oscillations in solar-like oscillators tend to follow an approximately regular pattern in which oscillation modes of a certain degree and consecutive order appear at regular intervals in frequency, i.e. the so-called large frequency separation. This is true to first order approximation for acoustic modes. However, to a second order approximation it is evident that the large frequency separation changes as a function of frequency. This frequency dependence has been seen in the Sun and in other main-sequence stars. However, from observations of giant stars, this effect seemed to be less pronounced. We investigate the difference in frequency dependence of the large frequency separation between main-sequence and giant stars using YREC evolutionary models.