Exploring the unexpected: Disharmonized harmonic pulsation modes in high-amplitude $\delta$ Scuti stars

Abstract

Harmonics are a ubiquitous feature across various pulsating stars. They are traditionally viewed as mere replicas of the independent primary pulsation modes and have thus been excluded from asteroseismological models. Recent research, however, has uncovered a significant discrepancy: in high-amplitude $\delta$ Scuti (HADS) stars, harmonics exhibit uncorrelated variations in amplitude and frequency relative to their independent primary pulsation modes. The nature of these disharmonized harmonics is a question of critical importance. In our study we analysed five triple-mode HADS stars observed by the Transiting Exoplanet Survey Satellite (TESS) and discovered some pervasive patterns of disharmonized harmonics in both the fundamental ($f_0$) and first overtone ($f_1$) pulsation modes. Intriguingly, through an in-depth frequency interaction analysis of V1393 Cen, we identified $2f_1$ as an independent pulsation mode, distinct from $f_1$, and identified it as the progenitor of the frequency variations observed in $3f_1$, $4f_1$, $5f_1$, and $6f_1$. Similar behaviour can be found in DO CMi and GSC 06047-00749, in which $2f_1$ and $3f_1$ are the independent pulsation modes, respectively. Notably, we found an interesting pattern when decomposing the harmonics that might suggest a generation process of harmonics. These findings serve as a new window on the research of harmonics, which remains a hidden corner of contemporary asteroseismology.

arXiv comment12 pages, 15 figures, 1 table. A&A Letter published

References in corpus (25)

• The Kepler characterization of the variability among A- and F-type stars. I. General overview
• Probing the interior physics of stars through asteroseismology
• Amplitude modulation in $\delta$ Sct stars: statistics from an ensemble study of Kepler targets
• Signatures of internal rotation discovered in the Kepler data of five slowly pulsating B stars
• A unifying explanation of complex frequency spectra of gamma Dor, SPB and Be stars: combination frequencies and highly non-sinusoidal light curves
• Evidence for nonlinear resonant mode coupling in the Beta Cep star HD 180642 (V1449 Aql) from CoRoT space-based photometry
• Combination Frequencies in the Fourier Spectra of White Dwarfs
• High frequency A-type pulsators discovered using SuperWASP
• Evidence of resonant mode coupling and the relationship between low and high frequencies in a rapidly rotating A star
• Monitoring a high--amplitude Delta Sct star for 152 days: discovery of 12 additional modes and modulation effects in the light curve of CoRoT 101155310
• Pulsational Frequency and Amplitude Modulation in the $\delta$\,Sct star KIC\,7106205
• KIC5950759: a high-amplitude $\delta$ Sct star with amplitude and frequency modulation near the terminal age main sequence
• EPIC 201585823, a rare triple-mode RR Lyrae star discovered in K2 mission data
• Delta Scuti Variables
• Asteroseismology of the Double-Mode High-Amplitude $\delta$ Scuti Star VX Hydrae
• DY Pegasi: An SX Phoenicis Star in a Binary System with an Evolved Companion
• Photometry of GSC 762-110, a new triple-mode radially pulsating star
• Asteroseismology of the double-radial mode $\delta$ Scuti star BP Pegasi
• Frequency analysis of Delta Scuti stars towards the Galactic bulge
• The imprint of star formation on stellar pulsations
• Frequency analysis of OGLE-IV photometry for classical Cepheids in Galactic fields: non-radial modes and modulations
• Unveiling the Intricate Symphony of Nonlinear Pulsation Mode Interactions in High-Amplitude $\delta$ Scuti Stars
• Modeling of multimode radially pulsating High-Amplitude Delta Scuti stars from the OGLE Galactic bulge sample
• A rapidly evolving high-amplitude $\delta$ Scuti star crossing the Hertzsprung Gap
• Uncorrelated Amplitude and Frequency Variations of the Harmonics in SX Phoenicis Star XX Cygni

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