Verlag der Oesterreichischen Akademie der Wissenschaften
Communications in Asteroseismology vol:157 pages:52-55
The mysterious amplitude and phase modulation observed in many RR Lyrae stars has puzzled astronomers for more than a century. Most commonly quoted hypotheses to explain the phenomenon involve nonradial modes, through either resonances or magnetic fields. However, their reality is still being questioned. Maybe an unknown physical mechanism in the star causes the main radial mode to change its properties over time while no nonradial pulsation modes are involved. Changing Blazhko periods challenge the existing models for the Blazhko effect. Because of its ability to describe a quasi-periodic time series in a simple way, we used the VSAA (Variable Sine Algorithmic Analysis, Tsantilas & Rovithis-Livaniou 2008) in a first and elementary application to monitor the changing Blazhko period of RR Lyr. Assuming modulation of a single pulsation frequency, we applied the VSAA to an extensive data set of RR Lyr, one of the best studied Blazhko stars. The results show how the amplitude and period of the modulation have changed over the past decades.