Chromospheric reversals in the emergence of an ephemeral region
THEMIS SL, c/ vía Láctea s/n, 38200 La Laguna, Tenerife, Spain e-mail: email@example.com
2 Instituto de Astrofísica de Canarias, c/ vía Láctea s/n, 38200 La Laguna, Tenerife, Spain
3 THEMIS, CNRS UPS 853, c/ vía Láctea s/n, 38200 La Laguna, Tenerife, Spain
Accepted: 1 March 2007
Context.The behaviour of both ephemeral regions and moving magnetic features has been often described for the photospheric layer, but not for the chromosphere. Both magnetic structures are related to the decay of active regions, but their actual role is not yet clear.
Aims.Our aim is to observe and understand the behaviour of these structures in the chromosphere.
Methods.We performed simultaneous photospheric and chromospheric spectropolarimetric observations of an ephemeral region and a moving magnetic feature. A new code developed for the reduction of spectropolarimetric data of several wavelengths observed simultaneously was used here for the first time and will be described here for future reference. The resulting Stokes profiles are analysed in detail.
Results.The Stokes V profiles of Fe i 6301 and 6302 Å are reversed in polarity with respect to the chromospheric Ca ii 8498 and 8542 Å in the cases shown. They reveal a reversed magnetic field topology between these layers for both structures. The time evolution of the ephemeral region results in a cancellation of the chromospheric signal, while the ratio of Stokes V amplitudes of Fe i 6301 and 6302 Å simultaneously informs us of a strengthening of the photospheric field. A scenario of the evolution of the ephemeral region is consequently suggested.
Conclusions.The moving magnetic feature reveals itself as an exclusively photospheric feature, similar to the ephemeral region in the initial stages of its emergence. As the loop emerges into the chromosphere it is slowed down and does not reach the corona. Most probably, the opposite polarity background in the chromosphere prevents ascent into corona.
Key words: Sun: magnetic fields / Sun: chromosphere / techniques: polarimetric
© ESO, 2007