EDP Sciences
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Volume 430, Number 2, February I 2005
Page(s) 567 - 569
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20042138

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. Pittard1

1  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 )

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