MSDP of THEMIS
as a magnetograph Method using a grid at the prime-focus (by P.Mein, J-M Malherbe.)
Texte .txt
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We present the
very first tests performed with the MSDP of THEMIS to measure magnetic
fields on May 9, 2000.
The MSDP produces
2D-images of the same area of the Sun, in 16 wavelength channels covering
the D1 line profile, and 2 polarization states simultaneously.
A grid is put in the prime focus. The width of the slits is roughly equal to the
analyzer separation and the step of the grid is twice this value. A scan of 3 exposures (step 11") is used to restore a full strip of ~140" X 9".
We present results obtained on a 140" X 120" area, by a scan of 24 strips.
The maps are computed by the bisector technique at +/-0.24 A from line center: intensity
fluctuations (top), B// magnetic field, Doppler velocity V// (bottom).
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Conclusions with
respect to the main advantages of the MSDP:
1 - Spatial resolution: The
seeing quality did not allow to take full advantage of the pixel size (0.18"
X 0.18") of the CCD (1536 X 1024). Better seeing conditions should produce
higher spatial resolutions in the future.
2 - Time resolution: The present
camera and computers need about 7mn to complete a scan. But the sum of
exposure times is only 3 X 24 X 0.2s =14.4s for the whole field of view.
Scanning times down to 30s should be possible with fast detectors (instability
studies, scanning by the earth for accurate positions of magnetic tracers).
