The extraordinary frequency pattern variation in {\delta} Scuti stars

TL;DR

This study investigates the unexpected diversity of frequency patterns in delta Scuti stars, revealing that each star exhibits a unique pattern unrelated to its physical parameters, challenging existing pulsation models.

Contribution

It introduces a quantitative measure of frequency pattern similarity and demonstrates the lack of correlation between observed patterns and stellar parameters.

Findings

Strong correlation in models with similar parameters when including rotational splitting

No correlation found in observed stars, indicating unique frequency patterns

Challenges current understanding of stellar pulsation mechanisms

Abstract

Inspection of the periodograms of TESS delta Scuti stars indicates that there is little, if any, similarity between the frequencies of stars in the same region of the H-R diagram. This is difficult to understand because pulsation models predict that stars with similar physical parameters should have similar frequencies. To investigate the problem, a quantitative measure of similarity between frequency patterns is described. When applied to non-adiabatic pulsation models with similar temperatures and luminosities, a strong correlation is found between the frequency patterns, as expected. The correlation increases when rotational frequency splitting is included. When applied to observations, no correlation can be found, confirming the impression from visual inspection. It seems that each star has its own unique frequency pattern, unrelated to its position in the H-R diagram. This presents a problem in our understanding of stellar pulsation. The existence of a period-luminosity law and the effect of combination frequencies in delta Scuti stars is briefly discussed.