Dynamical condensation in a thermally bistable flow. Application to interstellar cirrus
P. Hennebelle, M. Pérault;
AaA, 1999, 351, 309
ABSTRACT:Astrophysical multi-phase media display rich spatial structures, as for example the cold cirrus clouds found in the neutral atomic
interstellar medium.
Condensation of cold structures in locally compressed
regions of turbulent thermally bistable flows is a plausible, not exclusive,
origin for the structuration of the medium.
Simulations in plane-parallel
geometry show that trans-sonic convergent flows of warm gas can indeed produce
long-lived cold condensations, whose properties are consistent with cirrus
observations.
Self-similar, non-isobaric, analytical solutions capable of describing the
beginning of the condensation process in the context of a convergent cooling flow
are derived.
The quantitative conditions for condensation are
discussed (size and velocity thresholds) as functions of the ambient
pressure.
The process efficiency is also addressed as well as the long-term
evolution.
Although the simplified framework proposed leaves aside important features of
realistic 3-d flows, we argue that compression-induced condensation within
trans-sonic flows, at scales close to the size threshold, is a central mechanism in
the formation of interstellar structures.
KEYWORDS: hydrodynamics, instabilities, ism: kinematics and dynamics, ism: structure, ism: clouds
CODE: hennebelle99