Journal Article

On the properties of strange modes

Hideyuki Saio, Norman H. Baker and Alfred Gautschy

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 294, issue 4, pages 622-634
Published in print March 1998 | ISSN: 0035-8711
Published online March 1998 | e-ISSN: 1365-2966 | DOI:
On the properties of strange modes

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Properties of the so-called strange modes occurring in linear stability calculations of stellar models are discussed. The behaviour of these modes is compared for two different sets of stellar models, for very massive zero-age main-sequence stars and for luminous hydrogen-deficient stars, both with high luminosity-to-mass ratios. We have found that the peculiar behaviour of the frequencies of the strange modes with the change of a control parameter is caused by the pulsation amplitude of a particular eigenmode being strongly confined to the outer part of the envelope, around the density inversion zone. The frequency of a strange mode changes because the depth of the confinement zone changes with the control parameter. Weakly non-adiabatic strange modes tend to be overstable because the amplitude confinement quenches the effect of radiative damping. On the other hand, extremely non-adiabatic strange modes become overstable because the perturbation of radiation force (gradient of radiation pressure) provides a restoring force that can be out of phase with the density perturbation. We discuss this mechanism by using a plane-parallel two-zone model.

Keywords: stars: chemically peculiar; stars: oscillations; stars: variables: other

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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