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Astron. Astrophys. 344, 709-717 (1999)

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On features of Faraday rotation of the decametric radio emission in the Jovian magnetosphere

V.E. Shaposhnikov 1, M.Y. Boudjada 2, H.O. Rucker 2, V.V. Zaitsev 1 and M. Aubier 3

1 Institute of Applied Physics, Russian Academy of Sciences, Uljanov St. 46, 603600 Nizhny Novgorod, Russia
2 Space Research Institute, Austrian Academy of Sciences, Halbaerthgasse 1, A-8010 Graz, Austria
3 Observatoire de Meudon, F-92195 Meudon, France

Received 8 June 1998 / Accepted 5 January 1999

Abstract

Jovian decametric emission exhibits a high degree of linear polarization. During its propagation the radiation crosses the Jovian magnetosphere and the terrestrial ionosphere which involves Faraday rotation of the polarization ellipse. We develop the basic equation necessary to estimate the amount of Faraday rotation of the polarization ellipse of the Jovian decametric emission in the different plasmas crossed by the emission, assuming that the different emission frequencies f are emitted from different regions. This assumption modifies the equation adding a new term [FORMULA], the coefficient C which depends on the Jovian magnetospheric plasma inhomogeneity across the emission ray paths. This term being taken into consideration gives the possibility to investigate the Jovian magnetospheric plasma inhomogeneity across the emission ray paths due to the Faraday rotation measurements. Using spectropolarimeter observations performed at the Nançay Observatory (France) we derive the wave ellipse orientation allowing to get the total amount of Faraday rotation [FORMULA] between the source and the observer. We find that the amount of rotation could as well be described by two approximate formulae: the quadratic ([FORMULA] is a function of [FORMULA] and [FORMULA]) and the parabolic ([FORMULA] is a function of [FORMULA] and [FORMULA]). This ambiguous result is due to the limited number of the experimental data and the short frequency band of the observations. We calculate the rotation measure along the propagation path from the source at Jupiter to the observer and the value of the position angle of the polarization ellipse at the emission point and estimate the characteristic latitude scale of the Io torus inhomogeneity. We find that within the same data set the use of different approximate formulae leads to different estimations of the rotation measure and position angle. Besides, we show that an incorrect choice of the frame interval of the polarization ellipse angle can lead to an essential error on the estimation of this angle.

Key words: polarization – planets and satellites: individual: Jupiter – radio continuum: solar system

Send offprint requests to: V.E. Shaposhnikov

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© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999
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