The Shocking Properties of Supersonic Flows: Dependence of the Thermal Overstability on M, alpha, and T_c/T_0

Details The Shocking Properties of Supersonic Flows: Dependence of the Thermal Overstability on M, alpha, and T_c/T_0 The Shocking Properties of Supersonic Flows: Dependence of the Thermal Overstability on M, alpha, and T_c/T_0

2005-04-28

arxiv.org/abs/astro-ph/0504640v1

Astronomy and Astrophysics

Astrophysics

12 pages, 12 figures, accepted by A&A

Scientific paper

10.1051/0004-6361:20042260

We investigate the Mach number dependence of the radiative overstability of shocks. We find that the stability of radiative shocks increases with decreasing Mach number, with the result that M=2 shocks require cooling exponents < -1.2 to be overstable. The frequency of oscillation of the fundamental mode has a strong Mach number dependence. We find that feedback between the cooling region and the cold dense layer (CDL) further downstream is a function of Mach number, with stronger feedback and oscillation of the boundary between the CDL and the cooling region occuring at lower Mach numbers. This feedback can be quantified in terms of the reflection coefficient of sound waves. An interesting finding is that the stability properties of low Mach number shocks can be dramatically altered if the shocked gas is able to cool to temperatures less than the pre-shock value, and it is probable that low Mach number astrophysical shocks will be overstable in a variety of situations. The results of this work are relevant to astrophysical shocks with low Mach numbers, such as supernova remnants (SNRs) immersed in a hot interstellar medium (e.g., within a starburst region), and shocks in molecular clouds, where time-dependent chemistry can lead to overstability. (Abridged)

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