Spectropolarimetry with the Hida Domeless Solar Telescope

We developed a spectropolarimetry system with a ferroelectric liquid crystal polarization modulator for the 60-cm Domeless Solar Telescope of Hida Observatory. The telescope is equipped with two oblique-reflection mirrors, that alter the incident polarization before it reaches the polarimeter. Furthermore, it is impossible to calibrate the polarimeter using unpolarized light because of the instrumental polarization. Here, we develop a procedure to obtain the parameters of both the instrumental polarization and for the calibration of the polarimeter from the same calibration data sets. We apply the new procedure to carry out high-sensitivity spectropolarimetry. It is now possible to measure the polarizations of various photospheric and chromospheric lines with the Domeless Solar Telescope.