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Switch shocks in molecular clouds. II. Implications

Smith, M.D. (1993) Switch shocks in molecular clouds. II. Implications. Astrophysical Journal, 406 (2). pp. 520-527. ISSN 0004-637X. (doi:10.1086/172464) (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)

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A method for analyzing shocks in molecular clouds with oblique magnetic fields has been developed (Paper I). Here I derive some of the basic observable properties of these C-type waves. In particular, switch shocks, in which the initial motion is parallel to the field lines, is explored and compared to the transverse case. The process of switching on the tangential component, to enable field-cushioning, leads to higher temperatures over a narrower shocked layer. Nevertheless ambipolar diffusion and acceleration of molecular material via shocks remains effective even along field lines. Switch shocks are present for a wide range of cloud parameters, with typical breakdown speeds of 30 and 50 km s-1 for molecular hydrogen densities of 106 and 104 cm-3, respectively. These are comparable to the standard transverse values of 45 and 50 km s-1 under the same conditions. Implications for molecular emission lines are explored. Switches and transverse shocks have similar properties. Switches produce less H2 emission and significantly higher excitation levels are possible. However, a strong low-temperature coolant (such as H2O) is necessary to avoid the appearance of a C* or J-type subshock. Ramifications for star formation and circumstellar disks are discussed. Torzsional switches and poloidal switches extract angular momentum and magnetic flux from molecular cloud cores at super-Alfvénic speeds.

Item Type: Article
DOI/Identification number: 10.1086/172464
Uncontrolled keywords: ISM: clouds, 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 10:41 UTC
Last Modified: 29 May 2019 15:55 UTC
Resource URI: (The current URI for this page, for reference purposes)
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