  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 V445 Lyr (KIC 6186029) which was observed with the Kepler
space mission. V445 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,
V445 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_sun) and luminosity (40-50 L_sun) of V445 Lyr through
theoretical Petersen diagrams. A non-radial mode as well as possibly the first
overtone are also excited. Furthermore, V445 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 V445 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.
