RR Lyrae stars seen from space

TL;DR

High-precision space photometry from CoRoT and Kepler has revealed complex, multifaceted behaviors in RR Lyrae stars, including irregular Blazhko effects, low-amplitude frequencies, and phenomena like period doubling, challenging previous simplistic models.

Contribution

This paper summarizes new observational insights into RR Lyrae stars obtained from space telescopes, highlighting their complex pulsation behaviors and the need to revise existing models.

Findings

Detection of irregular and cycle-to-cycle changes in the Blazhko effect.

Identification of low-amplitude frequencies and phenomena like period doubling.

Evidence that RR Lyrae stars are more complex than previously thought.

Abstract

RR Lyrae stars for a long time had the reputation of being rather simple pulsators, but the advent of high-precision space photometry has meanwhile changed this picture dramatically. This article summarizes the results obtained for two remarkable Blazhko RR Lyrae stars and discusses how our view of RR Lyrae stars has changed since the availability of ultra-precise satellite photometry as it is obtained by CoRoT and Kepler. Both stars, CoRoT 105288363 and V445 Lyrae, show a multitude of phenomena that were impossible to observe from the ground, either because of the small amplitude of the effect, or because uninterrupted long-term monitoring was required for a detection. Not only was it found that strong and irregular cycle-to-cycle changes of the Blazhko effect can occur, and that seemingly chaotic phenomena need to be accounted for when modeling the Blazhko effect, but also a rich spectrum of low-amplitude frequencies was detected in addition to the fundamental radial pusation in RRab stars. The so-called period doubling phenomenon, higher radial overtones and possibly also non-radial modes make RR Lyrae stars more multifaceted than previously thought. This article presents the various aspects of irregularity of the Blazhko effect, questioning its long-standing definition as a "periodic modulation", and also discusses the low-amplitude pulsation signatures that had been hidden in the noise of observations for centuries.