Abstract
Rosette modes compose a peculiar group of oscillation modes in rotating stars. Although they have been investigated in some theoretical works, it has not been clear yet whether these modes are excited in real stars or not. In order to study this problem, a stability analysis of the modes is performed. It turns out that some rosette modes are unstable due to the kappa mechanism in a model of slowly pulsating B stars. It is also examined how unstable rosette modes can transport angular momentum in stars.
Highlights
Rosette modes are a class of eigenmodes of oscillations that are found in rotating stars
Their frequencies are in the range of gravity modes, but not below twice the rotation frequency, the domain in which the Coriolis force plays a dominant role in the oscillation motion
In order to discuss whether the rosette modes can be excited in real stars or not, we examine the stability of oscillation modes of a 5 M zero-age main sequence (ZAMS) model, which can be regarded as a representative model of slowly pulsating B stars [7, 8]
Summary
Rosette modes are a class of eigenmodes of oscillations that are found in rotating stars. The modes have been discovered recently by accident [1] in numerical computations of oscillation modes of uniformly rotating polytropic models, when physical properties of gravito-inertial modes in rapidly rotating stars are studied [2]. The key point is considerable interaction caused by the second-order effect of the Coriolis force among multiple eigenmodes that have almost the same frequencies (close degeneracy) in the non-rotating limit. The possibility of such (close) degeneracy has already been recognised before in the perturbative treatment of the effect of rotation on stellar oscillations [e.g. 4]. The lines with different colours indicate different values of the azimuthal order, m
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