Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005mnras.357..707r&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 357, Issue 2, pp. 707-721.
Astronomy and Astrophysics
Astronomy
3
Hydrodynamics, Instabilities, Shock Waves, Ism: Kinematics And Dynamics, Ism: Molecules
Scientific paper
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 Λ~ρβTα and a specific heat ratio of γ, we determine the overstability regime in the parameter space consisting of α, β and γ. In general, if α is sufficiently low, the fundamental mode leads to long-wavelength growing oscillations. For the fundamental mode, we find that values of γ corresponding to molecular hydrodynamics lead to a significantly restricted instability range for α in comparison with 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 displaying 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 dynamical rippling overstability, the cooling overstability is suppressed for a sufficiently low specific heat ratio.
Ramachandran Babulakshmanan
Smith Michael D.
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