Letter to the Editor

Discovery of resonating integration modes in triple-mode high-amplitude δ Scuti stars: A new evolutionary phase indicator

¹ Institute of Theoretical Physics, Shanxi University, Taiyuan 030006, China
² State Key Laboratory of Quantum Optics Technologies and Devices, Shanxi University, Taiyuan 030006, China
³ Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
⁴ Department of Physics, Taiyuan Normal University, Jinzhong 030619, China
⁵ Institute of Computational and Applied Physics, Taiyuan Normal University, Jinzhong 030619, China
⁶ Shanxi Key Laboratory for Intelligent Optimization Computing and Blockchain Technology, Jinzhong 030619, China

^⋆ Corresponding author: jsniu@sxu.edu.cn

Received: 18 February 2025
Accepted: 3 May 2025

Abstract

High-amplitude δ Scuti stars (HADS) that pulsate in their first three radial modes are rare in current samples. Here, we analyse five such triple-mode HADS observed by the Transiting Exoplanet Survey Satellite (TESS) and report that the previously considered second overtone mode (f₂) is actually the non-radial component of a resonating integration mode (RI mode, resulting from resonance between a radial p-mode and a non-radial p-g mixed mode), which shows significant amplitude and frequency variations over short timescales (approximately 20 days). This RI mode appears to be widespread among these stars. Notably, all five stars are in the post-main sequence evolutionary phase, actively crossing the Hertzsprung gap. These stars offer valuable insights into stellar evolution during the Hertzsprung gap, which is one of the most rapid evolutionary stages in a star’s life.