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Nonlinear asteroseismology: insight from amplitude and frequency modulations of oscillation modes in Kepler compact pulsators
Weikai Zong (IRAP, CNRS/Universite de Toulouse), Stéphane Charpinet (IRAP, Université de Toulouse/CNRS, France), Gérard Vauclair (IRAP, Université de Toulouse/CNRS, France), Noemi Giammichele (1. IRAP, Universite dé Toulouse/CNRS, France; 2. Département de Physique, Université de Montréal, Canada), et al.
Nonlinear mode interactions are difficult to observe from ground-based telescopes as the typical periods of the modulations induced by those nonlinear phenomena are on timescales of weeks, months, even years. The launch of space telescopes, e.g., Kepler, has tremendously changed the situation and shredded new light on this research field. We present results from Kepler photometry showing evidence that nonlinear interactions between modes occur in the two compact pulsators KIC 08626021, a DB white dwarf, and KIC 10139564, a short period hot B subdwarf. KIC 08626021 and KIC 10139564 had been monitored by Kepler in short-cadence for nearly two years and more than three years without interruption, respectively. By analyzing these high-quality photometric data, we found that the modes within the triplets induced by rotation clearly reveal different behaviors: their frequencies and amplitudes may exhibit either periodic or irregular modulations, or remain constant. These various behaviors of the amplitude and of the frequency modulations of the oscillation modes observed in these two stars are in good agreement with those predicted within the amplitude equation formalism.in the case of the nonlinear resonant mode coupling mechanism.