The all-sky GEOS RR Lyr survey with the TAROT telescopes. Analysis of the Blazhko effect

Abstract

We used the GEOS database to study the Blazhko effect of galactic RRab stars. The database is continuously enriched by maxima supplied by amateur astronomers and by a dedicated survey by means of the two TAROT robotic telescopes. The same value of the Blazhko period is observed at different values of the pulsation periods and different values of the Blazhko periods are observed at the same value of the pulsation period. There are clues suggesting that the Blazhko effect is changing from one cycle to the next. The secular changes in the pulsation and Blazhko periods of Z CVn are anticorrelated. The diagrams of magnitudes against phases of the maxima clearly show that the light curves of Blazhko variables can be explained as modulated signals, both in amplitude and in frequency. The closed curves describing the Blazhko cycles in such diagrams have different shapes, reflecting the phase shifts between the epochs of the brightest maximum and the maximum O-C. Our sample shows that both clockwise and anticlockwise directions are possible for similar shapes. The improved observational knowledge of the Blazhko effect, in addition to some peculiarities of the light curves, have still to be explained by a satisfactory physical mechanism.

13 pages, 12 figures, accepted for publication in Astronomical Journal

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• Overtone and multi-mode RR Lyrae stars in the globular cluster M3
• Cyclic variations in O-C diagrams of field RR Lyrae stars as a result of LiTE
• Bright Blazhko RRab Lyrae stars observed by ASAS and the SuperWASP surveys
• The historical vanishing of the Blazhko effect of RR Lyr from GEOS and Kepler surveys
• Known Galactic field Blazhko stars
• A cautionary tale of interpreting O-C diagrams: period instability in a classical RR Lyr Star Z CVn mimicking as a distant companion
• Finest light curve details, physical parameters, and period fluctuations of CoRoT RR Lyrae stars
• Blazhko type fundamental-mode RR Lyrae stars in the globular cluster, M3
• Four 'Peculiar' RRd Stars Observed by K2
• Two Different Weak Modulations in ab-type RR Lyrae Variable V838 Cyg, and Potential Influence of Metal Abundance on Blazhko Modulation
• The elusive chase for the first RR Lyr star in a binary system: the case of KIC 2831097