Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008mnras.386.1959g&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 386, Issue 4, pp. 1959-1965.
Astronomy and Astrophysics
Astronomy
5
Sun: Activity, Sun: Magnetic Fields, Sun: Photosphere
Scientific paper
Based on the spectral scan data of NOAA AR 10325, 10484 and 10377 obtained with the Solar Magnetic Field Telescope at Huairou Solar Observing Station, we analyse the azimuthal differences (Δδφ) between the line centre and the line wing -0.12 Å of FeI λ5324.19 caused by Faraday rotation. Grids of the longitudinal field Bz and inclination ψ for intervals of 100 G and 3° are made. It is found that the azimuthal rotations are of the same magnitude when Bz is in a 100-G interval. The amplitudes of azimuthal differences obviously increase with increasing Bz and decrease with increasing ψ. Averaging Δδφ in each 100-G interval of Bz and making a linear fit between <Δδφ> and Bz, then we obtain the correlation between the observed azimuthal difference and Bz depicted by the linear fitting formula (1), namely Δδφo = 0.0114|Bz|. In addition, through the simulation we also obtain the azimuthal rotation at the line centre of FeI λ5324.19 described by the fitting formula (2), namely δφ0.00 = 0.0254|Bz| - 3.975 × 10-6B2z. We also present a third fitting formula (3), namely Δδφt = 0.0149|Bz| - 1.455 × 10-6B2z, which describes the azimuthal differences between the line centre and the line wing -0.12 Å. Formula (3) is consistent with the observational results of the three active regions. We correct the vector magnetograms of the three active regions with formulae (1) and (3) and find that the electric current Jz, the current helicity Hc, and the average force-free field factor αav calculated from the correct magnetograms are nearly equivalent to those measured at the line wing -0.12 Å. Furthermore, we calculate Jz with 393 corrected vector magnetograms and find that formulae (1) and (3) can remove part of the false current whereas formula (2) can remove most of it.
Gao Yanfang
Su Jiangtao
Xu Haiqing
Zhang Hongqi
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