Asymptotic theory of gravity modes in rotating stars II. Impact of
general differential rotation
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by
Vincent Prat, Stéphane Mathis, Kyle Augustson, François
Lignières, Jérôme Ballot, Lucie Alvan, Allan Sacha Brun
2018
Abstract
Context. Differential rotation has a strong influence on stellar internal
dynamics and evolution, notably by triggering hydrodynamical instabilities, by
interacting with the magnetic field, and more generally by inducing transport
of angular momentum and chemical elements. Moreover, it modifies the way waves
propagate in stellar interiors and thus the frequency spectrum of these waves,
the regions they probe, and the transport they generate.
Aims. We investigate the impact of a general differential rotation (both in
radius and latitude) on the propagation of axisymmetric gravito-inertial waves.
Methods. We use a small-wavelength approximation to obtain a local dispersion
relation for these waves. We then describe the propagation of waves thanks to a
ray model that follows a Hamiltonian formalism. Finally, we numerically probe
the properties of these gravito-inertial rays for different regimes of radial
and latitudinal differential rotation.
Results. We derive a local dispersion relation that includes the effect of a
general differential rotation. Subsequently, considering a polytropic stellar
model, we observe that differential rotation allows for a large variety of
resonant cavities that can be probed by gravito-inertial waves. We identify
that for some regimes of frequency and differential rotation, the properties of
gravito-inertial rays are similar to those found in the uniformly rotating
case. Furthermore, we also find new regimes specific to differential rotation,
where the dynamics of rays is chaotic.
Conclusions. As a consequence, we expect modes to follow the same trend. Some
parts of oscillation spectra corresponding to regimes similar to those of the
uniformly rotating case would exhibit regular patterns, while parts
corresponding to the new regimes would be mostly constituted of chaotic modes
with a spectrum rather characterised by a generic statistical distribution.
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