Chaos in large-amplitude pulsators: application to the beta Cep star HD180642

TL;DR

This paper proposes that chaos caused by nonlinear behavior of the dominant radial mode explains the complex frequency spectrum observed in the beta Cephei star HD180642, supported by long-term data analysis and simulations.

Contribution

It introduces chaos as a new explanation for the rich frequency spectrum in beta Cephei stars, contrasting with previous stochastic or resonance models.

Findings

Chaos explains spectral features and frequency shifts

Nonlinear analysis supports chaotic behavior

Mixture of linear and nonlinear oscillations observed

Abstract

The CoRoT observations of the beta Cephei star HD180642 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 nonlinear resonance. I argue for a third explanation for the observations, in the form of chaos due to the nonlinear 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. Nonlinear time series analysis techniques are applied to the CoRoT observations, and the observations are compared with simulations of a simple nonlinear 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 nonlinear oscillations complicate the nonlinear time series analysis techniques.