Abstract
We present the analysis of the CoRoT star 105288363, a new Blazhko RR Lyrae star of type RRab (f0 = 1.7623 c/d), observed with the CoRoT space craft during the second long run in direction of the galactic center (LRc02, time base 145 d). The CoRoT data are characterized by an excellent time sampling and a low noise amplitude of 0.07 mmag in the 2-12 c/d range and allow us to study not only the fine details of the variability of the star but also long-term changes in the pulsation behaviour and the stability of the Blazhko cycle. We use, among other methods, standard Fourier analysis techniques and O-C diagrams to investigate the pulsational behavior of the Blazhko star 105288363. In addition to the frequency pattern expected for a Blazhko RR Lyrae star, we find an independent mode (f1 = 2.984 c/d) showing a f0/f1 ratio of 0.59 which is similar to that observed in other Blazhko RR Lyrae stars. The bump and hump phenomena are also analysed, with their variations over the Blazhko cycle. We carefully investigated the strong cycle-to-cycle changes in the Blazhko modulation (PB = 35.6 d), which seem to happen independently and partly diametrically in the amplitude and the phase modulation. Furthermore, the phasing between the two types of modulation is found to change during the course of the observations.
Highlights
RR Lyrae stars are low-mass stars on the horizontal branch that burn helium in their core
RR Lyrae stars can pulsate in the radial fundamental mode (RRab stars), in the first radial overtone (RRc stars) or in both modes simultaneously (RRd stars)
Most multiplet components are hidden, not in the noise, but in an irregular pattern of unresolved peaks that are caused by the cycle-to-cycle changes of the Blazhko modulation
Summary
RR Lyrae stars are low-mass stars on the horizontal branch that burn helium in their core. While hydrodynamical simulations successfully reproduced period doubling (Szabo, Kollath & Molnar 2010; Kollath, Molnar & Szabo 2011) and found a 9:2 resonance between the ninth overtone which appears as a surface mode and the fundamental pulsation to be responsible for the phenomenon, they were not able to yield modulated light curves It was an alternative approach by Buchler & Kollath (2011), using the amplitude equation formalism, that succeeded in producing amplitude modulation of both regular and irregular types. Chaos occurs because of the presence of a strange attractor in the dynamics, causing irregular behaviour Changes in both the amplitude and/or the length of the Blazhko cycles, irregularities in the Blazhko phenomenon, sometimes accompanied by a change in the main pulsation period, have been reported for a sample of RR Lyrae stars. The main differences between the results of the two manuscripts are briefly summarized in Appendix A
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