156 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
Inversion of stellar fundamental parameters from Espadons and Narval high-resolution spectra
The general context of this study is the inversion of stellar fundamental
parameters from high-resolution Echelle spectra. We aim indeed at developing a
fast and reliable tool for the post-processing of spectra produced by Espadons
and Narval spectropolarimeters. Our inversion tool relies on principal
component analysis. It allows reduction of dimensionality and the definition of
a specific metric for the search of nearest neighbours between an observed
spectrum and a set of observed spectra taken from the Elodie stellar library.
Effective temperature, surface gravity, total metallicity and projected
rotational velocity are derived. Various tests presented in this study, and
done from the sole information coming from a spectral band centered around the
Mg I b-triplet and with spectra from FGK stars are very promising.Comment: 13 pages, 8 figures (accepted A&A). arXiv admin note: text overlap
with arXiv:1401.108
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
Principal component analysis-based inversion of effective temperatures for late-type stars
We show how the range of application of the principal component
analysis-based inversion method of Paletou et al. (2015) can be extended to
late-type stars data. Besides being an extension of its original application
domain, for FGK stars, we also used synthetic spectra for our learning
database. We discuss our results on effective temperatures against previous
evaluations made available from Vizier and Simbad services at CDS.Comment: Accepted for publication in A&
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