Infrared Spectro-Polarimeter of the Solar Flare Telescope at NAOJ

A new infrared spectro-polarimeter was installed in 2008 onto the Solar Flare Telescope of NAOJ in the Mitaka headquarters. The Solar Flare Telescope had been operated previously as a filter-based magnetograph and obtained vector magnetograms of active regions with the Fe I 630.3nm line during 1992 - 2005. The aim of this new instrument is to measure the distribution of magnetic helicity over the whole Sun and for an extended period with high magnetic sensitivity in the infrared wavelengths. This spectro-polarimter is able to obtain polarizations in both photospheric and chromospheric layers. In order to take full Stokes profiles, we observe Fe I 1564.8 nm and He I 1083.0 nm lines (with the neighboring photospheric Si line) for the photospheric and chromospheric magnetic field vectors, respectively. The infrared detector of this instrument is a $640{\times}512$-pixel InGaAs camera produced by a Belgian company Xenics. The frame rate of the camera is 90 frames/sec. The 640-pixel row of this camera is set along the spectrograph slit of the polarimeter. Since the slit only covers the solar hemisphere, a full disk map is obtained by raster scanning the solar disk twice. A magnetic map is made of about $1200{\times}1200$ pixels with a pixel size of 1.8 arcsec. It generally takes 1.5 hours to scan the whole Sun. Although some issues on the instrument calibration still remain, a few maps of the whole Sun at the two wavelengths are now taken daily. In this presentation, we will introduce the instrument and present some observational results.