Bibcode
Ruiz-Cobo, B.; Puschmann, K. G.
Referencia bibliográfica
The Astrophysical Journal, Volume 745, Issue 2, article id. 141 (2012).
Fecha de publicación:
2
2012
Revista
Número de citas
8
Número de citas referidas
5
Descripción
The aim of this work is the determination of the twist, writhe, and
self-magnetic helicity of penumbral filaments located in an inner
sunspot penumbra. For this purpose, we inverted data taken with the
spectropolarimeter on board Hinode with the SIR (Stokes Inversion based
on Response function) code. For the construction of a three-dimensional
geometrical model we applied a genetic algorithm minimizing the
divergence of vec{B} and the net magnetohydrodynamic force,
consequently a force-free solution would be reached if possible. We
estimated two proxies to the magnetic helicity frequently used in
literature: the force-free parameter α z and the
current helicity term h_{c_{z}}. We show that both proxies are only
qualitative indicators of the local twist as the magnetic field in the
area under study significantly departs from a force-free configuration.
The local twist shows significant values only at the borders of bright
penumbral filaments with opposite signs on each side. These locations
are precisely correlated to large electric currents. The average twist
(and writhe) of penumbral structures is very small. The spines (dark
filaments in the background) show a nearly zero writhe. The writhe per
unit length of the intraspines diminishes with increasing length of the
tube axes. Thus, the axes of tubes related to intraspines are less wrung
when the tubes are more horizontal. As the writhe of the spines is very
small, we can conclude that the writhe reaches only significant values
when the tube includes the border of an intraspine.
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