Interstellar shock waves with magnetic precursors

The structure of steady, radiative, one-dimensional shock waves in partially ionized gas with a transverse magnetic field B<SUB>0</SUB> is investigated. Under a broad range of conditions applicable to the interstellar medium it is found that such shocks may be preceded by a 'magnetic precursor' which heats and compresses the medium ahead of the front where the neutral gas undergoes a discontinuous change of state; indeed, if B<SUB>0</SUB> is sufficiently large, a shock can exist with no discontinuities in hydrodynamical variables. Within this 'magnetic precursor' both ions and electrons stream through the neutral fluid with velocities which may be a significant fraction of the shock speed. The physical processes operative in such shocks are examined, including the effects of charged dust grains in dense molecular clouds. Numerical examples are shown for 10 km/s shocks propagating into diffuse H I or H2.

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