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Resonant Excitation of Nonradial Modes in RR Lyrae Stars

Rafal M. Nowakowski
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Abstract

A nonlinear development of radial pulsation instability to a resonant excitation of nonradial modes is studied. The theory covers the cases of axisymmetric (m=0) modes as well as (m,-m) pairs. Adopting a simplified treatment of the mode coupling, it is found that multimode pulsation with constant amplitudes is a highly probable solution. An observable consequence of the m=0 mode excitation is randomness of pulsation amplitude. The case of an l=1 mode is the most important because of a small averaging effect and a large excitation probability. A significant amplitude and phase modulation is predicted in the case of excitation of an l=1,m=+/-1 pair. This may explain Blazhko-type modulation in RR Lyrae stars. If this model is correct, the modulation period is determined by the rotation rate and the Brunt-Vaisala frequency in the deepest part of the radiative envelope.

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Rafal M. Nowakowski. 2002-02-26. Resonant Excitation of Nonradial Modes in RR Lyrae Stars. https://arxiv.org/abs/astro-ph/0202482

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