Fast magnetohydrodynamic oscillations in a force-free line-tied coronal arcade

Free access article

Issue		A&A Volume 455, Number 2, August IV 2006


Page(s)		709 - 717
Section		The Sun
DOI		http://dx.doi.org/10.1051/0004-6361:20054430

A&A 455, 709-717 (2006)
DOI: 10.1051/0004-6361:20054430

Fast magnetohydrodynamic oscillations in a force-free line-tied coronal arcade

A. J. Díaz¹, T. Zaqarashvili² and B. Roberts¹

¹ Mathematical Institute, University of St Andrews, St Andrews, KY16 9SS, Scotland, UK
e-mail: [antonio;bernie]@mcs.st-and.ac.uk
² Departament de Física, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain
e-mail: temury.zaqarashvili@uib.es

(Received 27 October 2005 / Accepted 28 April 2006)

Abstract
Aims.We discuss a simple model of a line-tied coronal arcade with piecewise constant density to explore the effects of curvature on radially polarised fast modes.
Methods.A partial differential equation is derived for the velocity perturbation of the fast modes and it is solved analytically in terms of Bessel functions of half integer order, obtaining a dispersion relation.
Results.The properties of the modes are studied in terms of the parameters. All the modes are leaky under these conditions. Besides the usual kink and sausage modes, new families are described: the vertical, swaying (longitudinal), and rocking modes arise.
Conclusions.The damping rates are similar to observed rates. For thin arcades the modes are markedly different from those of a straight slab and resemble more the modes of a circular membrane.

Key words: Sun: oscillations -- Sun: magnetic fields -- Sun: corona

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