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Issue A&A Volume 369, Number 2, April II 2001 Page(s) 646 - 659 Section The Sun DOI 10.1051/0004-6361:20010120

A&A 369, 646-659 (2001)
DOI: 10.1051/0004-6361:20010120

Empirical models of solar magnetic flux-tubes and their non-magnetic surroundings

C. Frutiger¹ and S. K. Solanki<sup>2

1</sup>  Institute of Astronomy, ETH-Zentrum, 8092 Zürich, Switzerland
²  Max-Planck-Institut für Aeronomie, 37191 Katlenburg-Lindau, Germany

(Received 21 July 2000 / Accepted 12 January 2001 )

Abstract
A powerful method for the analysis of the structure of small scale magnetic elements in the solar photosphere is the inversion of Stokes spectra. In previous papers based on such inversions Bellot Rubio et al. (1997, 1999) and Frutiger et al. (1999) have argued in favor of models with rather different dynamic properties. In this paper we return to this debate and compare results returned by inversions based on new multi-component models applied to several Fe I, Fe II and C I spectral line profiles obtained in active region plage with a Fourier Transform Spectrometer. These inversions differ from earlier ones by the fact that mass conservation is strictly imposed both inside the magnetic elements and on the surrounding external flow field. These flux-tube models are not only able to reproduce the characteristic Stokes V asymmetries and line-shifts observed in active regions plages or network elements, but also the Stokes I line profiles, including line bisectors. It is confirmed that from the quality of the fits alone it is not possible to distinguish between the steady flow proposed by Bellot Rubio et al. (1997) and the oscillatory model of Frutiger & Solanki (1998). If, however, physical constraints are imposed (e.g. mass conservation or that the flow retains the same direction over height in the flux tube) then the oscillatory model is found to be superior. In addition, the current investigation also provides the first inversion-based model of abnormal granulation.

Key words: polarization -- radiative transfer -- Sun: faculae, plages -- Sun: granulation -- Sun: magnetic fields

Offprint request: C. Frutiger, frutiger@astro.phys.ethz.ch

© ESO 2001

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