First Kepler results on RR Lyrae stars

TL;DR

This study analyzes Kepler data of RR Lyrae stars, revealing a high incidence of the Blazhko effect, additional frequencies suggestive of period doubling, and providing insights into their pulsation behaviors over a 3.5-year span.

Contribution

It presents the first Kepler-based analysis of RR Lyrae stars, confirming the high prevalence of the Blazhko effect and discovering period doubling phenomena.

Findings

Over 40% of RR Lyrae stars show the Blazhko effect.

Detection of additional frequencies indicating period doubling.

Kepler data enables unprecedented study of RR Lyrae pulsations.

Abstract

We present the first results of our analyses of selected RR Lyrae stars for which data have been obtained by the Kepler Mission. As expected, we find a significant fraction of the RRab stars to show the Blazhko effect, a still unexplained phenomenon that manifests itself as periodic amplitude and phase modulations of the light curve, on time scales of typically tens to hundreds of days. The long time span of the Kepler Mission of 3.5 yrs, and the unprecedentedly high precision of its data provide a unique opportunity for the study of RR Lyrae stars. Using data of a modulated star observed in the first roll as a showcase, we discuss the data, our analyses, findings, and their implications for our understanding of RR Lyrae stars and the Blazhko effect. With at least 40% of the RR Lyrae stars in our sample showing modulation, we confirm the high incidence rate that was only found in recent high-precision studies. Moreover, we report the occurrence of additional frequencies, beyond the main pulsation mode and its modulation components. Their half-integer ratio to the main frequency is reminiscent of a period doubling effect caused by resonances, observed for the first time in RR Lyrae stars.