Connections between the cycle-to-cycle light curve and O-C variations of the Blazhko RR Lyrae stars

TL;DR

This study investigates the link between cycle-to-cycle light curve variations and O-C diagram irregularities in Blazhko RR Lyrae stars, revealing a strong correlation with the Blazhko effect amplitude using Kepler data.

Contribution

It extends analysis of C2C light curve variations to Blazhko stars, demonstrating their significant role in O-C irregularities and their correlation with the Blazhko effect.

Findings

C2C variations are present in 74% of Blazhko stars' O-C diagrams.

The strength of C2C variations is larger in Blazhko stars than in non-Blazhko stars.

A strong positive correlation exists between C2C variation strength and Blazhko amplitude.

Abstract

Recent studies have shown that the irregular O-C variations observed in many non-Blazhko RR Lyrae stars may result from random, cycle-to-cycle (C2C) variations in their light curves. However, centuries-long data series reveal that the O-C diagrams of Blazhko stars exhibit particularly large-amplitude, irregular variations. In this Letter, we extend the previous investigation of non-Blazhko stars to Kepler Blazhko stars to explore the role of C2C variations in the O-C diagrams. We derived the O-C diagrams from Kepler space telescope light curves using a precise template-fitting method. Based on their Fourier analyses, we also constructed residual O-C diagrams that were pre-whitened for frequencies associated with the Blazhko effect. We then fitted the same statistical models to both types of O-Cs that we had previously applied to non-Blazhko stars. The optimal statistical model includes the C2C variation for 74% of the O-C curves in our Blazhko sample, and the parameter describing the strength of the C2C variation is significantly larger than that obtained for non-Blazhko stars. This may explain the strong irregular O-C variations previously observed in Blazhko stars. Furthermore, we found a strong positive correlation between the C2C variation strength and the amplitude of the frequency-modulation component of the Blazhko effect, indicating a connection between the two phenomena.