2013MNRAS.431.2554D

The CoRoT observations of the β Cephei star HD 180642 uncover an unexpectedly rich frequency spectrum, in addition to several heat-driven modes. So far, two processes have been proposed to explain this behaviour: the presence of stochastic oscillations and the excitation of time-dependent frequencies by non-linear resonance.

I argue for a third explanation for the observations, in the form of chaos due to the non-linear behaviour of the dominant radial mode.

The long-term frequency stability of the dominant radial mode is studied using archival data spanning roughly 20 years. Non-linear time series analysis techniques are applied to the CoRoT observations, and the observations are compared with simulations of a simple non-linear oscillator.

I show that chaos offers one single explanation for many of the observed features, such as the structure in the autocorrelation of the power spectrum, the long-term frequency shift, the power excess and the wide range of frequencies in the power spectrum. However, the mixture of opacity-driven linear oscillations and non-linear oscillations complicates the non-linear time series analysis techniques.