Amplitude and orientation of prominence magnetic fields from constant α magnetohydrostatic models
Pascal Demoulin Submitted: 2003-04-25 08:30
We analyze outputs from three-dimensional models for three
observed filaments, which belong to the quiescent, intermediate
and plage class respectively. Each model was calculated from a
constant α magnetohydrostatic extrapolation,
assuming that the prominence material is located in magnetic
dips, so that the field is nearly horizontal throughout
the prominence body and feet.
We calculate the spatial distribution of the magnetic field
amplitude B and orientation theta with respect to the filament
axis, neither of which were imposed a priori in the models.
In accordance with past magnetic field measurements within prominence
bodies, we also obtain nearly homogeneous magnetic fields, respectively
of about B ~ 3, 14 and 40 G for the quiescent, intermediate and
plage prominence, with a systematic weak vertical field gradient of
dB / dz ~ 0.1-1.5 X 10-4 G.km-1.
We also find that the inverse polarity configuration is dominant
with theta ~ -20 to 0 degrees, which is slightly
smaller than in some observations.
We also report some other properties, which have either
rarely or never been observed. We find at prominence tops
some localized normal polarity regions with theta < +10 degrees.
At prominence bottoms below 20 Mm in altitude, we find
stronger field gradients dB / dz ~ 1-10 X 10-4 G.km-1
and a wider range of field directions theta ~ -90 to 0 degrees.
These properties can be interpreted by the perturbation of the prominence flux tube by strong photospheric polarities located in the neighborhood of the prominence. We also report some full portions of prominences that have the normal polarity. The latter are simply due to
the local curvature of the filaments with respect to their
average axis, which was used to define theta.
These results could either be used as predictions for further
testing of this class of models with new observations, or as
quantitative tools for the interpretation of observations which
show complex patterns.
Authors: Aulanier, G., Demoulin, P.
Publication Status: 2003, A&A, 402, 769
Last Modified: 2003-04-25 08:30