469 research outputs found
Calibration of the 6302/6301 Stokes V line ratio in terms of the 5250/5247 ratio
Four decades ago the Stokes V line ratio in the Fe I 5247.06 and 5250.22
{\AA} lines was introduced as a powerful means of exploring the intrinsic field
strengths at sub-pixel scales, which led to the discovery that most of the
photospheric flux is in intermittent kG form. The "green" 5247-5250 line pair
is unique because it allows the magnetic-field effects to be isolated from the
thermodynamic effects. No other line pair with this property has since been
identified. In recent years much of the magnetic-field diagnostics has been
based on the "red" Fe I 6301.5 and 6302.5 {\AA} line pair, since it was chosen
in the design of the Hinode space observatory. Although thermodynamic effects
severely contaminate the magnetic-field signatures for this line ratio, it is
still possible to use it to extract information on intrinsic magnetic fields,
but only after it has been "renormalized", since otherwise it produces
fictitious, superstrong fields everywhere. In the present work we explore the
joint behavior of these two line ratios to determine how the "contaminated" red
line ratio can be translated into the corresponding green line ratio, which
then allows for a direct interpretation in terms of intrinsic magnetic fields.
Our observations are mainly based on recordings with the ZIMPOL-3
spectro-polarimeter at IRSOL in Locarno, Switzerland, complemented by data from
the STOP telescope at the Sayan solar observatory (Irkutsk, Russia). The IRSOL
observations are unique by allowing both the green and red line pairs to be
recorded simultaneously on the same CCD sensor. We show how the line ratios
depend on both the measured flux densities and on the heliocentric distance
(the \mu\ value on the solar disk), and finally derive the calibration function
that enables the red line ratio to be translated to the green ratio for each
\mu\ value
Atmospheric fluctuations below 0.1 Hz during drift-scan solar diameter measurements
Measurements of the power spectrum of the seeing in the range 0.001-1 Hz have
been performed in order to understand the criticity of the transits' method for
solar diameter monitoring.Comment: 3 pages, 3 figures, proc. of the Fourth French-Chinese meeting on
Solar Physics Understanding Solar Activity: Advances and Challenges, 15 - 18
November, 2011 Nice, Franc
First polarimetric observations and modeling of the FeH F^4 Delta-X^4 Delta system
Lines of diatomic molecules are more temperature and pressure sensitive than
atomic lines, which makes them ideal tools for studying cool stellar
atmospheres an internal structure of sunspots and starspots. The FeH F^4
Delta-X^4 Delta system represents such an example that exhibits in addition a
large magnetic field sensitivity. 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. We present for the first
time spectropolarimetric observations of the FeH F^4 Delta-X^4 Delta system
measured in sunspots to investigate their diagnostic capabilities for probing
solar and stellar magnetic fields. We investigate whether the current
theoretical model of FeH can reproduce the observed Stokes profiles including
their magnetic properties. The polarimetric observations 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. We find that the current theory successfully reproduces the
magnetic properties of a large number of lines in the FeH F^4 Delta-X^4 Delta
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. The
FeH F^4 Delta-X^4 Delta system is found to be a very sensitive magnetic
diagnostic tool. Polarimetric data of these lines provide us with more direct
information to study the coolest parts of astrophysical objects.Comment: 4 pages, 3 figure
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