A rapidly evolving high-amplitude $\delta$ Scuti star crossing the Hertzsprung Gap

TL;DR

This paper reports the discovery of a high-amplitude $\, ext{delta}$ Scuti star crossing the Hertzsprung gap, exhibiting rapid, large amplitude and frequency variations in multiple pulsation modes, with a new resonance-based interpretation.

Contribution

It introduces a new pulsation mode framework involving resonance between radial and nonradial modes to explain observed rapid variations.

Findings

Three independent pulsation modes with rapidly changing amplitudes and frequencies.

The observed period variation rates are significantly larger than standard seismic models.

Identification of a new resonating integration mode caused by mode resonance.

Abstract

In this work, we report the discovery of the rapidly evolving high-amplitude $\delta$ Scuti star KIC 6382916 (J19480292+4146558) which is crossing the Hertzsprung gap. According to the analysis of the archival data, we find three independent pulsation modes, whose amplitudes and frequencies vary distinctly in 4 years. The linear period variation rates of the first two modes are about 3-4 times larger than the best seismic model constructed by the standard evolution theory, while that of the third one is about 8 times larger than the first two modes. What is more interesting is that, almost all the combinations of the third mode have frequency peaks $0.0815\ \mathrm{c\ d}^{-1}$ away from them in the frequency domain. A framework is proposed to interpret the markedly large frequency and amplitude variation rates of the third mode, in which we employ a new pulsation mode (resonating integration mode) generated by the resonance between a radial p-mode and a nonradial mixed mode. Moreover, a global analysis of the interactions between the three independent pulsation modes and their harmonics/combinations is performed based on the interaction diagrams of their amplitudes and phases, which would be a useful tool for the future asteroseismology research.