The Drag Instability in a 1D Isothermal C-Shock. (arXiv:2007.05173v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Gu_P/0/1/0/all/0/1">Pin-Gao Gu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chen_C/0/1/0/all/0/1">Che-Yu Chen</a>
We investigate whether the drag instability, proposed by Gu et al., occurs in
a one-dimensional (1D) C-shock. The 1D background model proposed by Chen and
Ostriker for a steady isothermal C-shock is adopted, and a 1D isothermal linear
analysis is performed. We confirm the postulation of Gu et al. that the drift
velocity between the ions and the neutrals is sufficiently high within a
C-shock to allow for the drag instability. We also study the underlying physics
of the decaying modes in the shock and post-shock regions. The drag instability
is an overstability phenomenon associated with an exponentially growing mode of
a propagating wave. We find that the growing wave mode can only propagate
downstream within the shock and subsequently decay in the post-shock region.
The maximum total growth (MTG) for such an unstable wave before it is damped is
estimated in typical environments of star-forming clouds, which is
approximately 10-30 times larger than the initial perturbation at the modest
shock velocities and can be significantly enhanced several hundred times for a
stronger C-shock with a larger width.
We investigate whether the drag instability, proposed by Gu et al., occurs in
a one-dimensional (1D) C-shock. The 1D background model proposed by Chen and
Ostriker for a steady isothermal C-shock is adopted, and a 1D isothermal linear
analysis is performed. We confirm the postulation of Gu et al. that the drift
velocity between the ions and the neutrals is sufficiently high within a
C-shock to allow for the drag instability. We also study the underlying physics
of the decaying modes in the shock and post-shock regions. The drag instability
is an overstability phenomenon associated with an exponentially growing mode of
a propagating wave. We find that the growing wave mode can only propagate
downstream within the shock and subsequently decay in the post-shock region.
The maximum total growth (MTG) for such an unstable wave before it is damped is
estimated in typical environments of star-forming clouds, which is
approximately 10-30 times larger than the initial perturbation at the modest
shock velocities and can be significantly enhanced several hundred times for a
stronger C-shock with a larger width.
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