Issue |
A&A
Volume 473, Number 1, October I 2007
|
|
---|---|---|
Page(s) | L1 - L4 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:20078109 | |
Published online | 06 August 2007 |
Letter to the Editor
First polarimetric observations and modeling of the FeH F
–X
system
1
Institute of Astronomy, ETH Zurich, 8092 Zurich, Switzerland e-mail: nafram@astro.phys.ethz.ch
2
Tuorla Observatory, University of Turku, 21500 Pikkiö, Finland
3
Laboratoire d'Études Spatiales et d'Instrumentation en Astrophysique, Observatoire de Paris, Section de Meudon, 92195 Meudon Principal Cedex, France
4
Istituto Ricerche Solari Locarno, Via Patocchi, 6605 Locarno-Monti, Switzerland
Received:
18
June
2007
Accepted:
23
July
2007
Context.Lines of diatomic molecules are typically much more temperature and pressure sensitive than atomic lines, which makes them ideal,
complementary tools for studying cool stellar atmospheres as well as the internal structure of sunspots and starspots. The FeH
FX
system represents such an example that exhibits in addition a large magnetic field sensitivity. However,
the current theoretical descriptions of these transitions including the molecular constants involved are only based on intensity measurements because polarimetric observations have not been available so far, which limits their diagnostic value. Furthermore, the theory was optimized to reproduce energy levels and line strengths without taking the magnetic sensitivities into account.
Aims.We present for the first time spectropolarimetric observations of the FeH FX
system measured in sunspots
to investigate their diagnostic capabilities for probing solar and stellar magnetic fields. In particular, we investigate whether the
current theoretical model of FeH can reproduce the observed Stokes profiles including their magnetic properties.
Methods.The polarimetric observations of the FeH FX
system in Stokes I and V are compared with synthetic Stokes
profiles modeled with radiative transfer calculations. This allows us to infer the temperature and the magnetic field strength of the
observed sunspots.
Results.We find that the current theory successfully reproduces the magnetic properties of a large number of lines in the
FeH FX
system. In a few cases the observations indicate a larger Zeeman splitting than predicted by the
theory. There, our observations have provided additional constraints, which allowed us to determine empirical molecular constants.
Conclusions.The FeH FX
system is found to be a very sensitive magnetic diagnostic tool. Polarimetric data of these
lines, in contrast to intensity measurements, provide us with more direct and detailed information to study the coolest parts of
sunspot and starspot umbrae, and cool active dwarfs.
Key words: molecular processes / sun: magnetic fields / polarization / radiative transfer / line: formation / stars: magnetic fields
© ESO, 2007
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