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During Spring 1998 the FGE telescope has been transported to NOAO/NSO Kitt Peak (Arizona) to perform a series of tests of the optics to estimate its optical quality, and to evaluate the vector polarimeter performances. The McMath-Pierce Solar Telescope of NOAO/NSO was used in the integrated light mode to feed the FGE telescope with a collimated beam of 1.5 m in diameter. In that way we did not have to constantly move the FGE telescope to track the motion of the sun across the sky. This task was performed by the heliostat of the McMath telescope. The following images and magnetograms have been obtained using the FGE 1532 x 1024 CCD camera in its 8 bits resolution mode. Here are optical diagrams of the FGE telescope, and of its post focus optics .
Image of a sunspot group
recorded on June 21 1998. The Fabry-Perot filter bandpass was centered
in the core of the CaI 6122.2 line. The exposure time was 100 ms. The
black bar on the top left corner is approximately 1 second of arc long
(~ 720 km on the Sun), and the field of view is about 150"x100". This
image has been flat fielded and Fourier filtered (cut-off high-pass
filter). The low contrast in the solar granulation is mainly due to the
non optimal seeing (image distortion and blurring due to the Earth's
atmospheric turbulence) during the exposure.
Image of granulation near
the Sun center, also recorded on June 21 1998. The same setup and data
processing as for the above image has been used. Details on the order
of 1 second of arc or slightly better can be seen in the image.
Longitudinal magnetogram of a
sunspot group recorded on June 21 1998 with the Fabry-Perot
passband in the blue wing of the CaI 6122 line. On its right is also
shown the Kitt Peak medium resolution magnetogram of the same
region, rotated to match the orientation of our magnetogram. The Kitt
Peak magnetogram does NOT have the same scale as the FGE
magnetogram. White (black) means field lines pointing towards (away
from) the observer. The fine black and white pattern visible outside
the sunspot and the pores is very likely an artifact due to small
differences in the two polarization images produced by the Earth's
atmospheric turbulence. The magnetogram is built by computing the
normalized difference between the images for the left and the right
circular polarization. These two images are recorded with an interval
of a few seconds between each other, therefore they are not exactly the
same. Here is the Full
disk Kitt Peak medium resolution magnetogram (the observed active
region is located in the upper right quadrant). An animated magnetogram in which the
best white light image recorded on June 21 and the magnetogram are
alternatively shown on top of each other.
Linear polarization image
(Stokes Q) of the same active region
Linear polarization image
(Stokes U) of the same active region
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