Journal
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN
Volume 74, Issue 6, Pages 1344-1355Publisher
OXFORD UNIV PRESS
DOI: 10.1093/pasj/psac072
Keywords
instrumentation: polarimeters; Sun: magnetic fields; Sun: photosphere
Categories
Funding
- UCHUGAKU project of the Unit of Synergetic Studies for Space, Kyoto University
- JSPS KAKENHI [20684005, JP21J14036]
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The Tandem Etalon Magnetograph (TEM) is an instrument that achieves high polarimetric sensitivity and addresses spatial variation in the response matrix through calibration.
The Tandem Etalon Magnetograph (TEM) is one of the instruments of the Solar Magnetic Activity Research Telescope of Hida Observatory. The TEM is a partial disk (320 '' x 240 '') filter magnetograph which scans the wavelength around a Felline at 6303A and achieves polarimetric sensitivity of <5 x 10(-4) for each wavelength. To obtain the polarimeter response matrix of the instrument, we have carried out end-to-end polarization calibrations of the instrument. We have also measured the polarization characteristics of the polarization beam splitter (PBS), which is a crucial component of the instrument. As a result of end-to-end calibration, we found significant spatial variation in the response matrix across the field of view. From a laboratory test, we found that 1% of the magnitude of a circular diattenuation of the PBS was due to the retardation caused by the stress in the cube and the linear diattenuation of the film. Although the spatial variation across the field of view is more than 10 times larger, to achieve the polarimetric sensitivity of <5 x 10(-4) , this can be well explained by the polarization characteristic of the PBS and corrected by using the response matrix obtained in the end-to-end calibration. In addition, we also obtained the daily variation of the polarization property of the TEM. We found that the crosstalk from Stokes Q to V changes by an amount comparable to the tolerance through a day. In the present configuration, we require a pixel-by-pixel calibration every 100 min to meet the accuracy requirement.
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