Stability of a system with cosmic rays and waves

Free access article

Issue		A&A Volume 469, Number 3, July III 2007


Page(s)		829 - 837
Section		Astrophysical processes
DOI		http://dx.doi.org/10.1051/0004-6361:20066938

A&A 469, 829-837 (2007)
DOI: 10.1051/0004-6361:20066938

Stability of a system with cosmic rays and waves

Y.-Y. Lo¹ and C.-M. Ko²

¹ Institute of Astronomy, National Central University, Chung-Li, Taiwan 320, R.O.C.
e-mail: d909002@astro.ncu.edu.tw
² Institute of Astronomy, Department of Physics and Center for Complex Systems, National Central University, Chung-Li, Taiwan 320, R.O.C.
e-mail: cmko@astro.ncu.edu.tw

(Received 15 December 2006 / Accepted 27 March 2007)

Abstract
Aims.We investigate the the stability of a cosmic-ray plasma system using the hydrodynamic approach.
Methods.The system we are considering comprises cosmic rays and two oppositely propagating Alfvén waves. The thermal plasma flow is treated as a background, such that the feedback of the cosmic rays and waves is neglected. Steady-state solutions exist for the system, and when two waves are present, the steady state is non-uniform. Linear stability analysis on the steady-state solutions shows that for short wavelengths, large cosmic ray energy density, and small wave energy density the system is stable.
Results.We present in detail the case of uniform background flow. The system is most unstable in the upstream region and becomes stable in the downstream region in the linear regime for short-enough wavelengths. We also speculate on the implication of the instability.

Key words: ISM: cosmic rays -- magnetohydrodynamics (MHD) -- instability -- waves

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