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

Abstract

High-amplitude $\delta$ 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 ($f_2$) 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.

8 pages, 5 figures, 2 tables. Matched the published version (A&A Letter published)

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• KIC 3868420: A high-amplitude $\delta$ Scuti-$\gamma$ Dor hybrid star crossing the Hertzsprung gap
• Discovery and Characterization of Three New High-amplitude delta Scuti Stars from TESS Observations
• Harmonics as a Hidden Window into the Turbulent Convective Envelope of non-Blazhko RRab Stars
• BE Lyncis: A Pulsating Star in the Most Eccentric Binary with a Massive Unseen Companion