239 research outputs found
The magnetic field of solar prominences
In his famous monographs, Einar Tandberg-Hanssen writes that "the single,
physically most important parameter to study in prominences may be the magnetic
field. Shapes, motions, and in fact the very existence of prominences depend on
the nature of the magnetic field threading the prominence plasma". Hereafter we
sumarize recent contributions and advances in our knowledge about the magnetic
field of solar prominences. It mostly relies on high resolution and high
sensitivity spectropolarimetry made both in the visible and in the near
infrared.Comment: 6 pages, 3 figures, Procs. of the 2008 meeting of the French Society
of Astronomy and Astrophysics (SF2A
2D radiative modelling of He I spectral lines formed in solar prominences
We present preliminary results of 2D radiative modelling of He I lines in
solar prominences, using a new numerical code developed by us (Leger,
Chevallier and Paletou 2007). It treats self-consistently the radiation
transfer and the non-LTE statistical equilibrium of H and, in a second stage,
the one of He using a detailed atomic model. Preliminary comparisons with new
visible plus near-infrared observations made at high spectral resolution with
THeMIS are very satisfactory.Comment: 4 pages, 2 figures (to appear in the Procs. of Solar Polarization
Workshop #5, eds. Berdyugina, Nagendra and Ramelli), revised +2 citations,
better figure
Freeware solutions for spectropolarimetric data reduction
Most of the solar physicists use very expensive software for data reduction
and visualization. We present hereafter a reliable freeware solution based on
the Python language. This is made possible by the association of the latter
with a small set of additional libraries developed in the scientific community.
It provides then a very powerful and economical alternative to other
interactive data languages. Although it can also be used for any kind of
post-processing of data, we demonstrate the capabities of such a set of
freeware tools using THeMIS observations of the second solar spectrum.Comment: 4 pages, 2 figures (to appear in the Procs. of Solar Polarization
Workshop #5, eds. Berdyugina, Nagendra and Ramelli
2D non-LTE radiative modelling of He I spectral lines formed in solar prominences
The diagnosis of new high-resolution spectropolarimetric observations of
solar prominences made in the visible and near-infrared mainly, requires a
radiative modelling taking into account for both multi-dimensional geometry and
complex atomic models. Hereafter we contribute to the improvement of the
diagnosis based on the observation of He I multiplets, by considering 2D
non-LTE unpolarized radiation transfer, and taking also into account the atomic
fine structure of helium. It is an improvement and a direct application of the
multi-grid Gauss-Seidel/SOR iterative scheme in 2D cartesian geometry developed
by us. It allows us to compute realistic emergent intensity profiles for the He
I 10830 A and D3 multiplets, which can be directly compared to the simultaneous
and high-resolution observations made at THeMIS. A preliminary 2D multi-thread
modelling is also discussed.Comment: 6 pages, 9 figures, A&
Fast 2D non-LTE radiative modelling of prominences I. Numerical methods and benchmark results
New high-resolution spectropolarimetric observations of solar prominences
require improved radiative modelling capabilities in order to take into account
both multi-dimensional - at least 2D - geometry and complex atomic models. This
makes necessary the use of very fast numerical schemes for the resolution of 2D
non-LTE radiative transfer problems considering freestanding and illuminated
slabs. The implementation of Gauss-Seidel and successive over-relaxation
iterative schemes in 2D, together with a multi-grid algorithm, is thoroughly
described in the frame of the short characteristics method for the computation
of the formal solution of the radiative transfer equation in cartesian
geometry. We propose a new test for multidimensional radiative transfer codes
and we also provide original benchmark results for simple 2D multilevel atom
cases which should be helpful for the further development of such radiative
transfer codes, in general.Comment: 10 pages, 8 figures, accepted to A&
Numerical radiative transfer with state-of-the-art iterative methods made easy
This article presents an on-line tool (rttools.irap.omp.eu) and its
accompanying software ressources for the numerical solution of basic radiation
transfer out of local thermodynamic equilibrium (LTE). State-of-the-art
stationary iterative methods such as Accelerated -Iteration and
Gauss-Seidel schemes, using a short characteristics-based formal solver are
used. We also comment on typical numerical experiments associated to the basic
non-LTE radiation problem. These ressources are intended for the largest use
and benefit, in support to more classical radiation transfer lectures usually
given at the Master level.Comment: 8 pages, 5 figures, accepted for Eur. J. Phys. - see also (and use!)
http://rttools.irap.omp.e
Multi-line Stokes inversion for prominence magnetic-field diagnostics
We present test results on the simultaneous inversion of the Stokes profiles
of the He I lines at 587.6 nm (D_3) and 1083.0 nm in prominences (90-deg
scattering). We created datasets of synthetic Stokes profiles for the case of
quiescent prominences (B<200 G), assuming a conservative value of 10^-3 of the
peak intensity for the polarimetric sensitivity of the simulated observations.
In this work, we focus on the error analysis for the inference of the magnetic
field vector, under the usual assumption that the prominence can be assimilated
to a slab of finite optical thickness with uniform magnetic and thermodynamic
properties. We find that the simultaneous inversion of the two lines
significantly reduces the errors on the inference of the magnetic field vector,
with respect to the case of single-line inversion. These results provide a
solid justification for current and future instrumental efforts with multi-line
capabilities for the observations of solar prominences and filaments.Comment: 14 pages, 5 figures, 1 tabl
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