**AAS 204th Meeting, June 2004**

*Session 37 Solar Magnetic Fields and the Photosphere*

SPD Poster, Tuesday, June 1, 2004, 10:00am-7:00pm, Ballroom
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## [37.06] IR Vector Magnetic Fields I: Instrumental Polarization Correction

*S. A. Jaeggli (University of Arizona), M. J. Penn (National Solar Observatory)*

Instrumental polarization is evident in the spectra of
active region 10008 taken with the CSUN-NSO IR camera at the
McMath-Pierce telescope on June 24, 2002. Several iron lines
near 15650 Å in the spectra exhibit Zeeman splitting. Using
a technique described by Kuhn et. al. (1994) the original
polarization is restored. For all Zeeman split lines in the
spectra the corrected Stokes profiles for the Q and U
components show symmetry, while Stokes V is made
antisymmetric with no central component.

The observed Stokes vector is related to the true Stokes
vector through the formula S_{true} = M^{-1} S_{obs}
where M^{-1} is the inverse Mueller matrix. The
correction coefficients from the Kuhn method are used to
compute the inverse Mueller matrix for light path of the
entire system. The expected inverse Mueller matrix is
computed for the telescope at each scan time using a simple
model described by Bernasconi (1997) but assuming the n and
k values of the index of refraction are the same for each
mirror surface. A least squares technique is used to fit
this telescope model to the measured inverse Mueller matrix
for the system. The telescope model can account for most of
the measured cross-talk except for the observed Stokes Q to
Stokes V cross-talk which is thought to occur in the
polarimeter.

The author(s) of this abstract have provided an email address
for comments about the abstract:
jaeggli@noao.edu

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