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Resonant Excitation of Nonradial Modes in RR Lyr Stars

Rafal M. Nowakowski·Wojciech A. Dziembowski
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Abstract

We study a nonlinear development of radial pulsation instability to a resonant excitation of nonradial modes. Our theory covers the cases of axisymmetric (m=0) modes as well as (m,-m) pairs. Adopting a simplified treatment of the radial and nonradial mode coupling we find that the asymptotic state is a pulsation with constant amplitudes and we evaluate the relative amplitude of the nonradial component. Observable consequence of the m=0 mode excitation is a small period change and a more significant amplitude change, especially in the case of a dipole mode (l=1). Such a mode has a fairly large excitation probability. Significant amplitude and phase modulation is predicted in the case of excitation of a m=1,-1 pair. We suggest that this may explain Blazhko-type modulation in RR Lyr 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 interior.

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Rafal M. Nowakowski, Wojciech A. Dziembowski. 2001-05-09. Resonant Excitation of Nonradial Modes in RR Lyr Stars. https://arxiv.org/abs/astro-ph/0105141

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