First observations of W Virginis stars with K2: detection of period doubling

TL;DR

This study reports the first Kepler K2 observations of W Virginis stars, revealing period doubling and cycle-to-cycle variations, which suggest complex nonlinear pulsation dynamics in these variable stars.

Contribution

First analysis of W Virginis stars with Kepler K2 data, demonstrating period doubling and irregular variations, advancing understanding of their pulsation behavior.

Findings

Detection of period doubling in M80-V1

Cycle-to-cycle variations observed in KT Sco

Period changes confirmed in W Vir

Abstract

We present the first analysis of W Vir stars observed by the Kepler space telescope in the K2 mission. Clear cycle-to-cycle variation were detected in the light curves of KT Sco and the globular cluster member M80-V1. While the variations in the former star seems to be irregular on the short time scale of the K2 data, the latter appears to experience period doubling in its pulsation. Ground-based colour data confirmed that both stars are W Vir-type pulsators, while a comparison with historical photometric time-series data revealed drastic period changes in both stars. For comparison we reexamine ground-based observations of W Vir, the prototype of the class, and conclude that it shows period doubling instead of mode beating. These results support the notion that nonlinear dynamics plays an important role in the pulsation of W Virginis-type stars.