Wildly oscillating stars
Year: 2026
Type: article
Abstract: Aims. We investigate the origin of the dense, ridge-like frequency clusters observed in a subset of A- and F-type pulsating stars, which we refer to as ‘wildly oscillating’ stars (WOSs). These agglomerated frequency regions occupy a confined part of the frequency spectrum, typically below the fundamental radial mode, and they cannot be explained on the basis of classical pulsation theory. Methods. We analysed high-precision space photometry from Kepler and TESS, constructed échelle diagrams, and performed systematic searches for combination frequencies. We determined the expected fundamental radial mode using pulsation constants, period–luminosity relations, and stellar models to place the agglomerated regions in a seismic context. The rotational modulation was examined through phase-folded light curves and an amplitude–phase analysis, followed by tests of the binarity and geometric modulation scenarios. In addition, we computed non-adiabatic stability models for representative stellar parameters to assess whether standard excitation mechanisms reproduce the observed structures. Results. The WOS phenomenon is confined to a narrow region of the Hertzsprung-Russell diagram (HRD) near the overlap of the δ Sct and γ Dor instability strips. The observed ridge morphology and mode density cannot be reproduced by simple asymptotic g -mode behaviour, standard low-order p modes, binarity, or typical rotational splitting. In at least two stars (KIC 5443410 and KIC 9347095), a significant fraction of peaks in the agglomerated region can be explained as non-linear combination frequencies involving high-order g modes. However, these combinations require parent modes to be located within the agglomerated frequency band itself, indicating that intrinsic pulsation modes must be present there. Non-adiabatic stability calculations successfully reproduce the classical instability domains; however, they do not predict unstable modes with the observed density or organised ridge structure in the agglomerated region. Conclusions. The WOSs appear to represent a pulsational regime that is not captured by current models of mode excitation or rotational modulation. The agglomerated frequency phenomenon requires a mechanism that selects or excites a confined intermediate-frequency band and produces organised ridge structures within a narrow region of the stellar parameter space.
Source: Astronomy and Astrophysics
Institutions: DTU Space, Technical University of Denmark, University of Southern Queensland, University of Lancashire, North-West University, The University of Sydney, Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, California Institute of Technology, Centre National de la Recherche Scientifique, Université Paris Sciences et Lettres, Observatoire de Paris, Sorbonne Université, Laboratoire d’études spatiales et d’instrumentation en astrophysique, Aarhus University, University of Liège, University of Wrocław, Newcastle University, KU Leuven, Université de Montpellier, Laboratoire Univers et Particules de Montpellier
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Awards: G6172793357, G6248214521, G6764146023
OpenAlex ID: W7167729412