Blazhko RR Lyrae light curves as modulated signals

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 06/2011; 417(2). DOI: 10.1111/j.1365-2966.2011.19313.x
Source: arXiv

ABSTRACT We present an analytical formalism for the description of Blazhko RR Lyrae
light curves in which employ a treatment for the amplitude and frequency
modulations in a manner similar to the theory of electronic signal
transmitting. We assume monoperiodic RR Lyrae light curves as carrier waves and
modulate their amplitude (AM), frequency (FM), phase (PM), and as a general
case we discuss simultaneous AM and FM. The main advantages of this handling
are the following: (i) The mathematical formalism naturally explains numerous
light curve characteristics found in Blazhko RR Lyrae stars such as mean
brightness variations, complicated envelope curves, non-sinusoidal frequency
variations. (ii) Our description also explains properties of the Fourier
spectra such as apparent higher-order multiplets, amplitude distribution of the
side peaks, the appearance of the modulation frequency itself and its
harmonics. In addition, comparing to the traditional method, our light curve
solutions reduce the number of necessary parameters. This formalism can be
applied to any type of modulated light curves, not just for Blazhko RR Lyrae

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Available from: Robert Szabo, Sep 28, 2015
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    ABSTRACT: The Blazhko-phenomenon, the modulation of the pulsation of RR Lyrae stars remains one of the most stubborn unsolved problems of stellar pulsation. The recent idea of Stothers proposes that periodic variations in the properties of the convective envelope may be behind the amplitude and phase modulation. In this work we approximated the mechanism by introducing variations in the convective parameters of the Florida-Budapest hydrodynamic code and also by means of amplitude equations. We found that the process is only effective for long modulation periods, typically for more than hundred days, in agreement with the thermal time scales of the pulsation in RR Lyrae stars. Due to the slow response of the pulsation to the structure changes, short period, high amplitude Blazhko-modulation cannot be reproduced with this mechanism or would require implausible variations in the convective parameters on short time scales. We also found that the modulation of the mixing length results in strong differences between both the luminosity and radius variations and the respective phase modulations of the two quantities, suggesting notable differences between the energy output of the photosphere and the mechanical variations of the layers. The findings suggest that the convective cycle model is not well suited as a standalone mechanism behind the Blazhko-effect.
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