Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-05-09
Acta Astronomica, Vol 51, 2001, p.5
Astronomy and Astrophysics
Astrophysics
42 pages, 10 figures, published in Acta Astronomica
Scientific paper
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.
Dziembowski Wojciech A.
Nowakowski Rafal M.
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