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

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.