Direct numerical simulations of the -mechanism
I. Radial modes in the purely radiative case
Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 14 avenue Édouard Belin, 31400 Toulouse, France e-mail: firstname.lastname@example.org
Accepted: 17 February 2008
Context. We present a purely-radiative hydrodynamical model of the κ-mechanism that sustains radial oscillations in Cepheid variables.
Aims. We determine the physical conditions favourable for the κ-mechanism to occur inside a layer, with a configurable conductivity-hollow. We complete nonlinear direct numerical simulations (DNS) that initiate from these most favourable conditions.
Methods. We compare the results of a linear-stability analysis, applied to radial modes using a spectral solver, and a DNS, which is developed from a high-order finite difference code.
Results. We find that by changing the location and shape of the hollow, we can generate well-defined instability strips. For a given position in the layer, the amplitude and width of the hollow appear to be key parameters to vary to attain unstable modes driven by the κ-mechanism. The DNS, starting from the favourable conditions, confirm both the growth rates and the structures of linearly-unstable modes. Nonlinear saturation is produced by intricate couplings between excited fundamental mode and higher damped overtones.
Key words: hydrodynamics / instabilities / waves / stars: oscillations / methods: numerical
© ESO, 2008