Free access article

A&A 430, 567-569 (2005)
DOI: 10.1051/0004-6361:20042138

Cosmic ray moderation of the thermal instability

A. Y. Wagner¹, S. A. E. G. Falle², T. W. Hartquist¹ and J. M. Pittard<sup>1

1</sup>  School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
    e-mail: ayw@ast.leeds.ac.uk
²  Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, UK

(Received 7 October 2004 / Accepted 6 November 2004 )

Abstract
We apply the Hermite-Bieler theorem in the analysis of the effect of cosmic rays on the thermal stability of an initially uniform, static background. The cosmic rays were treated in a fluid approximation and the diffusion coefficient was assumed to be constant in time and space. The inclusion of cosmic rays does not alter the criterion for the thermal stability of a medium subjected to isobaric perturbations. It does alter the criteria for the stability of a medium perturbed by small amplitude sound waves. In the limit of a high background cosmic ray pressure to thermal pressure ratio, the instability in response to high frequency sound waves is suppressed.

Key words: ISM: kinematics and dynamics -- ISM: cosmic rays -- hydrodynamics -- instabilities

© ESO 2005

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