Harmonics as a Hidden Window into the Turbulent Convective Envelope of non-Blazhko RRab Stars

Abstract

Harmonics in pulsating stars have traditionally been regarded as mere Fourier artifacts, fully determined by their parent mode. Recent observations of high-amplitude $\delta$ Scuti stars, however, have revealed the existence of disharmonized harmonics, which exhibit amplitude and frequency variations uncorrelated with their parent pulsation mode. Here we test the universality of this phenomenon by examining a class of stars long considered pulsationally stable: non-Blazhko RRab stars. Using short-cadence {\it Kepler} photometric data, we not only identify a distinct hump structure formed by harmonics of the primary pulsation mode in their frequency spectra, but also find significant amplitude and frequency variations associated with the harmonics around the onset and in the tail of the hump structure. These findings are consistent with the interpretation that the hump structure originates from the turbulent convective envelope of the star. Interestingly, several important phenomena can be understood within this framework as a working hypothesis. Thus, the hump structure of harmonics and their intrinsic variability could constitute a hidden window into the stellar convective envelope, potentially tracing energy injection at the convection-pulsation interaction and stochastic perturbations from turbulent convection -- although detailed modeling is required to confirm this interpretation.

arXiv comment9 pages, 5 figures, 2 tables. Accepted for publication by A&A Letter

References in corpus (20)

• Understanding the Lomb-Scargle Periodogram
• Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
• Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
• Probing the interior physics of stars through asteroseismology
• Fourier analysis of non-Blazhko ab-type RR Lyrae stars observed with the Kepler space telescope
• Interaction Between Convection and Pulsation
• Signatures of nonlinear mode interactions in the pulsating hot B subdwarf star KIC 10139564
• EPIC 201585823, a rare triple-mode RR Lyrae star discovered in K2 mission data
• Are all RR Lyrae stars modulated?
• Revisiting the Kepler non-Blazhko RR Lyrae sample: Cycle-to-cyle variations and additional modes
• Finest light curve details, physical parameters, and period fluctuations of CoRoT RR Lyrae stars
• Unveiling the Intricate Symphony of Nonlinear Pulsation Mode Interactions in High-Amplitude $\delta$ Scuti Stars
• Frequency analysis of OGLE-IV photometry for classical Cepheids in Galactic fields: non-radial modes and modulations
• A rapidly evolving high-amplitude $\delta$ Scuti star crossing the Hertzsprung Gap
• On the connection between almost periodic functions and Blazhko light curves
• Uncorrelated Amplitude and Frequency Variations of the Harmonics in SX Phoenicis Star XX Cygni
• Discovery of resonating integration modes in triple-mode high-amplitude $\delta$ Scuti stars: A new evolutionary phase indicator
• Connections between the cycle-to-cycle light curve and O-C variations of the non-Blazhko RR Lyrae stars
• Exploring the unexpected: Disharmonized harmonic pulsation modes in high-amplitude $\delta$ Scuti stars
• Connections between the cycle-to-cycle light curve and O-C variations of the Blazhko RR Lyrae stars