Simulations of the wardle instability of c-type shock waves |
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| Authors: | G Tóth |
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| Institution: | (1) Dept. of Astrophysical Sciences, Princeton University, Princeton, USA;(2) Dept. of Atomic Physics, Eötvös University, Budapest, Hungary;(3) Present address: Astronomical Institute, Utrecht University, Postbus 80000, 3508 Utrecht, TA, The Netherlands |
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| Abstract: | C-type shocks in the partially ionized ISM are modelled by numerical simulations. Under certain conditions the shocks are subject to the Wardle instability, which initially makes the shock front rippled, then in the non-linear stage can produce density variations in both the ion and neutral fluids. A systematic search in the numerically accessible parameter space is done to determine the wave vector kmax and the growth rates
max of the fastest growing modes. The neutral Alfvén number, and the angle
sbetween the shock normal and the upstream magnetic field determine the strength and obliqueness of the shock, as well as the dimensionless parameters of the fastest growing mode. The results confirm and extend Wardle's linear analysis.The non-linear evolution shows saturation of the instability and the formation of high density regions that detach from the shock front with the downstream flow. Numerical difficulties are partially solved by an implicit treatment of the ion-neutral friction terms, but strong shocks still can not be modelled efficiently. A fully implicit method for the ions and the magnetic field is used to model C-type shocks with low fractional ionization and high ion Alfvén speed. |
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| Keywords: | ISM Shock Waves Instabilities MHD Methods: numerical |
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