Issue |
A&A
Volume 367, Number 3, March I 2001
|
|
---|---|---|
Page(s) | 1033 - 1048 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361:20000495 | |
Published online | 15 March 2001 |
Influence of magnetic fields on the coherence effects in the Nai D1 and D2 lines
1
Institute of Astronomy, ETH Zentrum, 8092 Zurich, Switzerland
2
National Solar Observatory, PO Box 26732, Tucson, AZ 85726-6732, USA
Corresponding author: J. O. Stenflo, stenflo@astro.phys.ethz.ch
Received:
1
September
2000
Accepted:
12
December
2000
To clarify the physical nature of the enigmatic scattering polarization
in the Na i D1 and D2 line cores we have explored
their behavior with full Stokes vector polarimetry in regions with
varying degree of magnetic activity near the solar limb. These
observations represent the first time that ZIMPOL II, the second
generation of our CCD based imaging polarimeter systems, has been used for
a scientific program. With ZIMPOL II the four Stokes images can be
demodulated and recorded with a single CCD sensor such that the resulting
images of the fractional polarization ,
, and
are
entirely free from spurious features due to seeing or flat-field
effects. The polarization in the cores of the lines, in particular in
D2, exhibits dramatic and unexpected spatial variations in both
and
, including polarization self-reversals of the D2
core peak. As the fluctuations in the Q, U, and V parameters
appear to be relatively uncorrelated, we have parametrized the profiles
and made scatter plots of the extracted parameters. Comparison with
synthetic scatter plots based on different theoretical models
suggests that the polarization signals in the cores of the D2 and
D1 lines have different physical origins: While the D1 core
is likely to be governed by ground-state atomic polarization,
the D2 core is dominated by the alignment of the excited state
and by effects of partial frequency redistribution.
Key words: polarization / scattering / Sun: magnetic fields / atomic processes / techniques: polarimetric
© ESO, 2001
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