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Resonant Excitation of Nonradial Modes in RR Lyrae Stars

Published online by Cambridge University Press:  12 April 2016

R. Nowakowski
R. Nowakowski*
Affiliation:
Copernicus Astronomical Center, Warsaw, Poland

Abstract

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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-Väisälä frequency in the deepest part of the radiative envelope.

Type
Part 3. Nonlinear Effects in Pulsating Stars
Information
International Astronomical Union Colloquium , Volume 185: Radial and Nonradial Pulsations as Probes of Stellar Physics , 2002 , pp. 408 - 411
Copyright
Copyright © Astronomical Society of the Pacific 2002

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