Astronomy & Astrophysics

Issue		A&A Volume 463, Number 1, February III 2007
Page(s)		333 - 338
Section		The Sun
DOI		10.1051/0004-6361:20065863

A&A 463, 333-338 (2007)
DOI: 10.1051/0004-6361:20065863

MHD seismology of coronal loops using the period and damping of quasi-mode kink oscillations

I. Arregui¹, J. Andries², T. Van Doorsselaere², M. Goossens², and S. Poedts²

¹ Departament de Física, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain
e-mail: inigo.arregui@uib.es
² Centrum voor Plasma Astrofysica, KU Leuven, Celestijnenlaan 200B, 3001 Heverlee, Belgium
e-mail: [Jesse.Andries;tomvd;Marcel.Goossens;Stefaan.Poedts]@wis.kuleuven.be

(Received 20 June 2006 / Accepted 11 November 2006 )

Abstract
Aims.We combine the magnetohydrodynamic (MHD) theory of resonantly damped quasi-mode kink oscillations with observational estimates of the period and damping of transverse coronal loop oscillations to extract information on physical parameters in oscillating loops.
Methods.A numerical study of the quasi-mode period and damping, in one-dimensional fully non-uniform flux tubes, is used to obtain equilibrium models that reproduce the observed periods and damping rates. This scheme is applied to 11 loop oscillation events.
Results.When only the damping rate is used, the valid equilibrium models form a one-dimensional solution curve in the two-dimensional parameter space (density contrast, transverse inhomogeneity length-scale). Lower limits to the transverse inhomogeneity are obtained in the limit of high contrast loops. When both the period and the damping rate are used, the equilibrium Alfvén speed (or Alfvén travel time) comes into play. The valid equilibrium models then form a one-dimensional solution curve in the three-dimensional parameter space (density contrast, transverse inhomogeneity length-scale, Alfvén speed or Alfvén travel time). The projection of these solutions onto the Alfvén speed axis is found to be constrained to a rather limited interval. Upper limits to the internal Alfvén speed are derived for 9 of the 11 analysed events.

Key words: magnetohydrodynamics (MHD) -- Sun: corona -- Sun: magnetic fields -- Sun: oscillations

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