Some Notes on the Modelling of Blazhko Effect

Some Notes on the Modelling of Blazhko Effect

Zoltán Kolláth

Although hydrodynamic models provide a good fit to most of the nonlinear phenomena in classical variable stars, no reliable models have existed for a long time for the Blazhko effect, a well-known property of RR Lyrae pulsations. During the last decades, several new models have been proposed to understand the puzzle of the Blazhko effect. Some of them are just mathematical considerations to provide a simple mechanism of modulations, lacking a real physical interpretation. Other models are based on results from numerical hydrodynamic calculations.
In parallel to the theoretical attempts to understand Blazhko modulation, space- and ground-based observations of RR Lyrae stars have uncovered a new level of complexity in the pulsation of these stars – new pieces of the great puzzle of RR Lyrae variability have been found. One of the most important recent findings is the limited modulation in the infrared observations. In connection, the radius of the inner layers oscillates in a very regular fashion, lacking significant modulations. It provides a strong physical constraint on all ideas. A satisfactory model has to provide a mechanism not only for the modulations but for all the dynamical effects found in the observations. We provide a reality check based on the observational facts on the possible theoretical models.
Although hydrodynamic models still contain lots of simplifications (1D approximation, lack of non-radial modes in nonlinear calculations, a crude approx- imation of turbulent convection) they display a very rich behaviour. High order resonances play a crucial role in the nonlinear dynamics representing the interact- ing modes. The richness of the found phenomena suggests that the interaction of multiple modes should be taken seriously in the understanding of observed features.

Proceedings of the Polish Astronomical Society, vol. 6, 137-145 (2018)

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