The Blazhko effect and additional excited modes in RR Lyrae stars

TL;DR

This study uses Kepler data to reveal that some RR Lyrae stars previously thought to lack the Blazhko effect actually exhibit it, linking the effect to additional pulsation modes and aiding in their detection.

Contribution

It demonstrates that non-Blazhko RRab stars with additional modes can host subtle Blazhko effects, refining understanding of pulsation behaviors in RR Lyrae stars.

Findings

Detected small amplitude Blazhko effects in two stars previously classified as non-Blazhko

Confirmed the link between the Blazhko effect and additional pulsation modes

Identified the smallest amplitude multiperiodic Blazhko effect in V350 Lyr

Abstract

Recent photometric space missions, such as CoRoT and Kepler revealed that many RR Lyrae stars pulsate -- beyond their main radial pulsation mode -- in low amplitude modes. Space data seem to indicate a clear trend, namely overtone (RRc) stars and modulated fundamental (RRab) RR Lyrae stars ubiquitously show additional modes, while non-Blazhko RRab stars never do. Two Kepler stars (V350 Lyr and KIC 7021124), however, apparently seemed to break this rule: they were classified as non-Blazhko RRab stars showing additional modes. We processed Kepler pixel photometric data of these stars. We detected small amplitude, but significant Blazhko effect for both stars by using the resulted light curves and O$-$C diagrams. This finding strengthens the apparent connection between the Blazhko effect and the excitation of additional modes. In addition, it yields a potential tool for detecting Blazhko stars through the additional frequency patterns even if we have only short but accurate time series observations. V350 Lyr shows the smallest amplitude multiperiodic Blazhko effect ever detected.