**AAS 197, January 2001**

*Session 42. Dust and Theory of ISM*

Display, Tuesday, January 9, 2001, 9:30am-7:00pm, Exhibit Hall
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## [42.14] Algebraic Solutions and Global Statistics of Colliding, Momentum-Conserving Thin Shells

*S. Stevenson (Wesleyan University), D. Chappell (University of La Verne), J. Scalo (University of Texas at Austin)*

We develop a set of parametric algebraic equations
describing the shape, velocity field, and surface density of
the interface layer formed between two colliding thin
shells. The solutions are exact in the limit that fluid
advection and momentum conservation of the shells dominate
both internal pressure effects and driving forces. Thus,
they are most appropriate to interactions between shells
when the zero-pressure snowplow assumption is valid. We
briefly examine the gravitational instability of the
interaction layer and compare the resulting growth rate with
the growth rate in the individual shells.

We also examine global statistics of pair-wise interactions
in a system of expanding shells using Monte-Carlo
simulations. The simulations may be relevant to either
interacting superbubbles driven by cluster winds or to the
interaction of smaller-scale shells driven by protostellar
winds. Results include the mass spectra of interaction
structures, velocity histograms, and dependence of the shell
collision rate on both the porosity of the interstellar
medium and the morphology of the interface layer.

The author(s) of this abstract have provided an email address
for comments about the abstract:
chappell@ulv.edu

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