Rapid and strong changes in the Blazhko modulation of RR Lyrae stars , as they have recently been detected in high precision satellite data , have become a crucial topic in finding an explanation of the long-standing mystery of the Blazhko effect .
We present here an analysis of the most extreme case detected so far , the RRab star V445Â Lyr ( KIC 6186029 ) which was observed with the Kepler space mission .
V445Â Lyr shows very strong cycle-to-cycle changes in its Blazhko modulation , which are caused both by a secondary long-term modulation period as well as irregular variations .
In addition to the complex Blazhko modulation , V445Â Lyr also shows a rich spectrum of additional peaks in the frequency range between the fundamental pulsation and the first harmonic .
Among those peaks , the second radial overtone could be identified , which , combined with a metallicity estimate of [ Fe/H ] =-2.0 dex from spectroscopy , allowed to constrain the mass ( 0.55-0.65 M _ { \odot } ) and luminosity ( 40-50 L _ { \odot } ) of V445Â Lyr through theoretical Petersen diagrams .
A non-radial mode as well as possibly the first overtone are also excited .
Furthermore , V445Â Lyr shows signs of the period doubling phenomenon and a long term period change .
A detailed Fourier analysis along with a study of the O-C variation of V445Â Lyr is presented , and the origin of the additional peaks and possible causes of the changes in the Blazhko modulation are discussed .
The results are then put into context with those of the only other star with a variable Blazhko effect for which a long enough set of high precision continuous satellite data has been published so far , the CoRoT star 105288363 .