The height of chromospheric loops in an emerging flux region

¹ Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Straße 2, Katlenburg-Lindau, Germany
e-mail: merenda@mps.mpg.de
² School of Space Research, Kyung Hee University, Yongin, Gyeonggi, 446-701 Korea

Received: 14 May 2010
Accepted: 1 June 2011

Abstract

Context. The chromospheric layer observable with the He i 10 830 Å triplet is strongly warped. The analysis of the magnetic morphology of this layer therefore requires a reliable technique to determine the height at which the He i absorption takes place.

Aims. The He i absorption signature connecting two pores of opposite polarity in an emerging flux region is investigated. This signature is suggestive of a loop system connecting the two pores. We aim to show that limits can be set on the height of this chromospheric loop system.

Methods. The increasing anisotropy in the illumination of a thin, magnetic structure intensifies the linear polarization signal observed in the He i triplet with height. This signal is altered by the Hanle effect. We apply an inversion technique incorporating the joint action of the Hanle and Zeeman effects, with the absorption layer height being one of the free parameters.

Results. The observed linear polarization signal can be explained only if the loop apex is higher than  ≈ 5 Mm. Best agreement with the observations is achieved for a height of 6.3 Mm.

Conclusions. The strength of the linear polarization signal in the loop apex is inconsistent with the assumption of a He i absorption layer at a constant height level. The determined height supports the earlier conclusion that dark He 10 830 Å filaments in emerging flux regions trace emerging loops.