The THEMIS telescope reveals the fine structure of the magnetic

e THEMIS telescope reveals the fine structure of the magnetic field at the solar surface outside of active re
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The THEMIS telescope reveals
the fine structure of the
magnetic field at the solar
surface outside of active
regions
Date de mise en ligne : vendredi 8 juillet 2016
Observatoire de Paris centre de recherche et enseignement en astronomie et
astrophysique relevant du Ministère de l'Enseignement supérieur et de la
Recherche.
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e THEMIS telescope reveals the fine structure of the magnetic field at the solar surface outside of active re
A key objective of the French THEMIS solar telescope, located in the Teide Observatory in
Tenerife in the Canary Islands, is to study the magnetic field and the motion of matter in
active and non-active regions of the Sun. Thanks to the high spatial resolution, it has been
possible for the first time to determine the flux tubes of the magnetic field, and the average
distance between two tubes outside sunspots. This result was obtained by V. Bommier, of the
Paris Observatory, from the measured polarization and inversion-based models.
At the Sun's surface, the magnetic field is highly variable from point to point outside sunspots and their surrounding
active regions. This is known since 1973 from the observation of two spectral lines of different magnetic sensitivity
(Stenflo, 1973). These observations had suggested that in the so-called quiet regions of the solar photosphere the
magnetic field is concentrated in vertical strong flux tubes. However, these fine structures are beyond the spatial
resolution of present solar observatories.
By combining modeling of such unresolved structures with observations made with the French THEMIS telescope
and the American SOT/SP experiment onboard the Japanese satellite HINODE, Véronique Bommier, astronomer at
the LESIA laboratory, has confirmed this fine structuring and has precisely characterized it.
By adding statistical methods of spatial correlation, the following parameters have been derived, namely : the
average flux tube diameter (30 km), the average distance between two flux tubes (230 km), and the average
magnetic field strength in the flux tube (1300 G, which is 0.13 T), in the quietest zones of the solar surface, where the
spatially averaged magnetic field is the weakest.
Représentation en fausses couleurs de l'angle d'inclinaison du vecteur champ magnétique par rapport à la
verticale solaire, dans et autour d'une tache solaire
Figure du bas : résultat de la modélisation dans
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e THEMIS telescope reveals the fine structure of the magnetic field at the solar surface outside of active re
l'hypothèse d'un champ magnétique homogène (tiré de http://jsoc.stanford.edu/ajax/lookdata.html).
du haut : résultat de la modélisation avec prise en compte de l'existence de tubes de flux.
Figure
The analysis of the magnetic field inclination has shown the flux tube opening out with height above the surface.
Thus, the solar quiet region magnetic field is a loop carpet made of opening and interconnected flux tubes. This is in
agreement with the present magnetic field models in such solar quiet regions.
Télescope THEMIS
Crédits image : Véronique Bommier
Reference
"Milne-Eddington inversion for unresolved magnetic structures in the quiet Sun photosphere", by Véronique
Bommier, published in Journal of Geophysical Research - Space Science.
This article will be included in the new version of the book "Measurement Techniques in Solar and Space Physics".
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