Summary: Mon. Not. R. Astron. Soc. 362, 13531362 (2005) doi:10.1111/j.1365-2966.2005.09406.x
A stability analysis of radiative shocks in the presence of a transverse
Babulakshmanan Ramachandran and Michael D. Smith
Armagh Observatory, College Hill, Armagh BT61 9DG
Accepted 2005 July 5. Received 2005 July 3; in original form 2005 April 1
Radiative shock waves may be subject to a global thermal instability in which the cooling layer
and shock front undergo growing resonant oscillations. For strong hydrodynamic shocks, the
presence of the overstability depends on the temperature and density indices of power-law
cooling functions and the specific heat ratio (, and , respectively). Here, we investigate
the stabilizing influence of a transverse magnetic field by introducing the shock Alfv´en number,
shocks under a wide range of conditions. In particular, we find that all molecular shocks in
which the cooling increases with the temperature ( > 0) are stabilized to the first four modes
if Ma < 20 ( = 2). For = -0.5, the first overtone remains stable only for Ma < 8.
We conclude that molecular shocks in the interstellar medium are probably stabilized by a
transverse magnetic field unless exceptional circumstances arise in which the cooling strongly
increases as the gas cools.
Key words: instabilities magnetic fields MHD shock waves ISM: molecules.