Amplitude and frequency variations of oscillation modes in the pulsating DB white dwarf star KIC 08626021 The likely signature of nonlinear resonant mode coupling

摘要: Context. The signatures of nonlinear effects affecting stellar oscillations are difficult to observe from ground observatories because the lack continuous high-precision photometric data spanning extended enough time baselines. unprecedented quality and coverage provided by Kepler spacecraft offers new opportunities search for these phenomena. Aims. We use accumulated on pulsating DB white dwarf KIC 08626021 explore in detail stability its oscillation modes, searching, particular, evidence behaviors. Methods. analyze nearly two years uninterrupted short-cadence data, concentrating identified triplets that caused rotation show intriguing behaviors during course observations. Results. find clear could be attributed resonant mode coupling mechanisms. These couplings occur between components can induce different types first notice a structure at 3681 μHz, as triplet previous published studies, is fact forming doublet, with third component being an independent mode. 4310 μHz this doublet (most likely visible incomplete triplet) have periodic frequency amplitude modulations, which typical so-called intermediate regime resonance, timescales consistent theoretical expectations. Another 5073 narrow transitory amplitudes modulated while frequencies locked. Using nonadiabatic pulsation calculations, based model representative evaluate linear growth rates modes triplets, we also provide quantitative information useful future comparisons numerical solutions equations. Conclusions. observed modulations clearest hints occurring stars so far. should resonate warning projects aim measuring evolutionary cooling rate 08626021, general. Nonlinear potentially jeopardize any attempt measure such reliably, unless they corrected beforehand. results motivate further work develop theory.