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		| Paper: | 
		Theory of Amplitude Modulation II. The Resonant Mode Interaction Model | 
	 
	
		| Volume: | 
		203, The Impact of Large-Scale Surveys on Pulsating Star Research, IAU Colloquium 176 | 
	 
	
		| Page: | 
		307 | 
	 
	
		| Authors: | 
		van Hoolst, T. | 
	 
	
	
		| Abstract: | 
		With about one fourth of the RRab stars showing the Blazhko effect, amplitude modulation on long time scales is a common phenomenon in stellar pulsation. The role of nonradial oscillation modes is studied here, and it is proposed that the amplitude modulation is a result of a dynamical, nonlinear resonance between the observed radial mode and a low-degree nonradial mode. In this scenario, a nonradial mode is resonantly excited in Blazhko-type RR Lyrae stars. Degree one modes are found to have the highest probability of being excited and a crucial test of the model would be the observational determination of the degree of the proposed nonradial mode. | 
	 
	
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