Chaotic dynamics in the pulsation of DF Cygni, as observed by Kepler

TL;DR

This study provides observational evidence of chaotic pulsations in the RVb-type star DF Cygni using Kepler data, revealing low-dimensional chaos as a key factor in its variability.

Contribution

First to demonstrate chaotic dynamics in the RVb subtype of RV Tauri stars using continuous Kepler observations and nonlinear analysis methods.

Findings

DF Cygni exhibits low-dimensional chaotic pulsations.

Lyapunov dimension of the chaos is approximately 2.8.

This is the first RVb star where chaos explains pulsation peculiarities.

Abstract

Pulsations of RV Tauri-type variable stars can be governed by chaotic dynamics. However, observational evidence for this happening is usually hard to come by. Here we use the continuous, 4-year-long observations of the Kepler space telescope to search for the signs of chaos in the RVb-type pulsating supergiant, DF Cygni. We use the Global Flow Reconstruction method to estimate the quantitative properties of the dynamics driving the pulsations of the star. The secondary, long-term light variation, i.e., the RVb phenomenon was removed in the analysis with the Empirical Mode Decomposition method. Our analysis revealed that the pulsation of DF Cyg could be described as a chaotic signal with a Lyapunov dimension of ~2.8. DF Cyg is only the third RV Tau star, and the first of the RVb subtype, where the nonlinear analysis indicates that low-dimensional chaos may explain the peculiarities of the pulsation.