Magnetic Field Structures in a Facular Region Observed by THEMIS and Hinode

TL;DR

This study compares vector magnetic maps of a facular region obtained by two spectropolarimeters, revealing small-scale magnetic structures and proposing a new method to estimate formation heights of spectral lines.

Contribution

It introduces a comparative analysis of magnetic field measurements from THEMIS and Hinode, and proposes a novel approach to determine relative formation heights of spectral lines in faculae.

Findings

Hinode SOT/SP resolves small magnetic polarities of 1-2 arcseconds.

Strong horizontal magnetic fields are observed in faculae.

Fe 6302.5 Å line forms at higher atmospheric height than Fe 5250.2 Å line.

Abstract

The main objective of this paper is to build and compare vector magnetic maps obtained by two spectral polarimeters, i.e. THEMIS/MTR and Hinode SOT/SP, using two inversion codes (UNNOFIT and MELANIE) based on the Milne-Eddington solar atmosphere model. To this end, we used observations of a facular region within active region NOAA 10996 on 23 May 2008, and found consistent results concerning the field strength, azimuth and inclination distributions. Because SOT/SP is free from the seeing effect and has better spatial resolution, we were able to resolve small magnetic polarities with sizes of 1" to 2", and we could detect strong horizontal magnetic fields, which converge or diverge in negative or positive facular polarities. These findings support models which suggest the existence of small vertical flux tube bundles in faculae. A new method is proposed to get the relative formation heights of the multi-lines observed by MTR assuming the validity of a flux tube model for the faculae. We found that the Fe 1 6302.5 \AA line forms at a greater atmospheric height than the Fe 1 5250.2 \AA line.