COOL C-SHOCKS AND HIGH-VELOCITY FLOWS IN MOLECULAR CLOUDS

C-shocks can be driven through dense clouds when the neutrals and magnetic field interact weakly due to a paucity of ions. We develop a method for calculating C-shock properties with the aim of interpreting the observed high-velocity molecular hydrogen. A high Mach number approximation, corresponding to low temperatures, is employed. Under strong cooling conditions the flow is continuous even though a subsonic region may be present downstream. Analytic expressions for the maximum temperature, dissociation fraction, self-ionization level and J-shock transition are derived. This allows a wide range of velocities, densities, magnetic fields and ionization fractions to be explored and the parameter ranges for C-shocks to be displayed. The maximum speed of C-shocks in dense regions remains in the range 30-50 kms-1 with the exceptions of high density (n≥107cm-3) and low H2O abundances or ionization fractions near or above 10-6, for which the maximum breakdown speed is significantly smaller. © 1990 Oxford University Press. All rights reserved.