Nonlinear Perturbations in Shock-bounded Slabs
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**Session 26 -- Interstellar Medium and Radiative Shocks**
*Oral presentation, Monday, 9, 1995, 10:00am - 11:30am*

## [26.07] Nonlinear Perturbations in Shock-bounded Slabs

*B. S. Marks (NCSU)*

Radiative shocks are relatively common in astrophysics, occuring in
accretion flows, stellar winds, stellar jets, supernovae, star
formation, and perhaps galaxy formation. In some cases the cooled gas
downstream of the radiative shock forms an isolated slab of dense gas.
If this slab is bounded on the other side by a radiative shock as well,
it is susceptible to a nonlinear dynamic instability (Vishniac, ApJ
428, 186). We have studied such shock-bounded slabs using numerical
hydrodynamics. Sinusoidal perturbations were added to planar slabs to
determine the characteristics of the dynamical evolution as a function
of the wavelength and amplitude of the perturbation relative to the
width of the slab. We confirm Vishniac's claim that perturbations with
amplitudes larger than the width of the slab are dynamically unstable:
the so-called "Nonlinear Thin Shell Instability" (NTSI). Given a
suitable initial perturbation and a sufficiently large Mach number, the
perturbation will grow unbounded. However, in many cases our results
show that the breathing mode of the perturbed slab can "outrun" the
shredding motion of the NTSI, causing the perturbations to pinch off
and form a relatively flat, albeit thick, slab that remains confined in
space. We have also investigated perturbations due to dense clouds
advected into an unperturbed planar slab. These perturbations often
lead to the NTSI effects as well.

This research was supported by an AAS REU award to North Carolina State University.

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