Blazhko Light Curves – Non-Modulated and Harmonic Detuned Signals

József M. Benkő

In this talk, I showed that two common assumptions concerning RR Lyrae light curves are invalid. (1) It was demonstrated that the presently best fitting mathematical model of Blazhko stars’ light curves is a Fourier representation of a general almost periodic function. It follows that, the widely used phrase ‘Blazhko modulation’ is at least not precise. Although many features of the Blazhko light curves can be described in the modulation framework, the real light curves are definitely not modulated signals. That is, the external modulation explanations of the Blazhko effect must be wrong, which gives a further support for those theoretical models which produce the effect as an inherent feature of the pulsation. (2) Up to now most studies assumed that the Fourier spectrum of the light curve of an RR Lyrae star, either monoperiodic or showing Blazhko effect, is dominated by the main pulsation frequency and its exact harmonics. The Fourier representation of the almost periodic function, however, contains frequency terms which systematically deviated from the harmonics. The previously published deviation of the harmonic frequencies of V445 Lyr is explained with the harmonic detuning effect predicted by the almost-periodic function framework. Using the original Kepler RRab data, an additional star (V2178 Cyg) has also been found showing this detuning effect.

Proceedings of the Polish Astronomical Society, vol. 6, 146-150 (2018)

Download full article as PDF file: