Analysis of the acoustic cut-off frequency and HIPs in six Kepler stars with stochastically excited pulsations

TL;DR

This study analyzes high-frequency pulsations in six Kepler stars to identify pseudo-modes and infer their acoustic cut-off frequencies, revealing insights into stellar structure and evolution through interference pattern analysis.

Contribution

It extends the methodology used on the Sun to other stars, uncovering pseudo-modes and analyzing interference patterns to infer cut-off frequencies and stellar properties.

Findings

Detected pseudo-modes in six Kepler stars.

Inferred cut-off frequencies from interference patterns.

Linked interference patterns to stellar structure and evolution.

Abstract

Gravito-acoustic modes in the Sun and other stars propagate in resonant cavities with a frequency below a given limit known as the cut-off frequency. At higher frequencies, waves are no longer trapped in the stellar interior and become traveller waves. In this article we study six pulsating solar-like stars at different evolutionary stages observed by the NASA Kepler mission. These high signal-to-noise targets show a peak structure that extends at very high frequencies and are good candidates for studying the transition region between the modes and the interference peaks or pseudo-modes. Following the same methodology successfully applied on Sun-as-a-star measurements, we uncover the existence of pseudo-modes in these stars with one or two dominant interference patterns depending on the evolutionary stage of the star. We also infer their cut-off frequency as the midpoint between the last eigenmode and the first peak of the interference patterns. By using ray theory we show that, while the period of one of the interference pattern is very close to half the large separation the other, one depends on the time phase of mixed waves, thus carrying additional information on the stellar structure and evolution.