| | |
Summary: Mon. Not. R. Astron. Soc. 000, 1{15 (2004) Printed 27 November 2004 (MN L A T E X style le v2.2)
On the linear analysis of unstable radiative shocks
Babulakshmanan Ramachandran ? & Michael D. Smithy
Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
Accepted ..... Received ..... ; in original form .....
ABSTRACT
We study the stability properties of strong hydrodynamic shocks and their associated
radiative cooling layers. We explore a range of conditions which covers both molecular
and atomic gas impacting against a rigid wall. Through a linear analysis employing a
cooling function of the form / T and a speci c heat ratio of
, we determine
the overstability regime in the parameter space consisting of , and
. In general, if
is suÆciently low, the fundamental mode leads to long wavelength growing oscilla-
tions. For the fundamental mode, we nd that values of
corresponding to molecular
hydrodynamics lead to a signi cantly restricted instability range for in comparison
to the shocks in a monatomic medium. The conditions for the growth of higher order
modes, however, are relatively unchanged. This predicts that certain molecular shocks
are prone to display signatures of small-scale rapid variability. Dissociative shocks,
however, can be subject to a large-scale overstability if subsequent molecule formation
in the cooling layer abruptly increases the cooling rate. In contrast to the dynami-
cal rippling overstability, the cooling overstability is suppressed for a suÆciently low
|
