Switch shocks in molecular clouds. I. Plane-parallel magnetohydrodynamic analysis

Smith, M.D. (1992) Switch shocks in molecular clouds. I. Plane-parallel magnetohydrodynamic analysis. Astrophysical Journal, 390 (2). pp. 447-453. ISSN 0004-637X. (doi:https://doi.org/10.1086/171295) (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided)

The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided. (Contact us about this Publication)
Official URL
http://dx.doi.org/10.1086/171295

Abstract

Magnetohydrodynamic shock waves in molecular clouds are discussed. Plane-parallel flows with oblique magnetic fields are analyzed with particular regard to switch shocks. Switch-on shocks occur in the limit as the flow and field directions coincide; a transverse field is then switched on by the shock. In molecular clouds these become continuous or C-type, here termed C-switches. Their existence rules out the alternative J-type hydrodynamic flows. J-switches are only possible at low Alfvén numbers even in strongly radiative shocks which possess an equilibrium temperature. C-switches yield both strong compression and large swings in the magnetic field direction. They arise under a wide range of general conditions. One requirement is that the Alfvén speed exceeds the sound speed. The other requirement, to keep the flow supersonic, is that A2/φ0 is small, where A is the Alfvén number and φ0 is a ratio of heating to cooling time scales. For transverse-field shocks the weaker restraint is on A/φ0. Upstream and downstream flow behavior is examined; weak downstream subshocks are more probable in C-switches than in transverse shocks. The temperature profile across an oblique shock is derived using the cool C-shock method. A formula is presented which determines the transverse shock of equivalent excitation. C-switch behavior influences flows within an angle ∼1/A of the field direction. Switch-off C-shocks, in which the field pressure generated by the switch-on shock is converted into thermal pressure as the transverse field disappears, are also discussed. An approximate isothermal solution is found.

Item Type: Article
Uncontrolled keywords: ISM: molecules, MHD shock waves
Subjects: Q Science > QB Astronomy > QB460 Astrophysics
Divisions: Faculties > Sciences > School of Physical Sciences > Centre for Astrophysics and Planetary Sciences
Depositing User: Giles Tarver
Date Deposited: 11 Aug 2015 10:42 UTC
Last Modified: 12 Aug 2015 16:29 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/50163 (The current URI for this page, for reference purposes)
  • Depositors only (login required):