Initial Results on Line-of-Sight Field Calibrations of SP/NFI Data Taken by SOT/Hinode

Abstract

Abstract We present initial results on the line-of-sight field calibration of the two kinds of Stokes $I$ and $V$ data taken by the Solar Optical Telescope on the satellite Hinode: spectral profiles of Stokes $I$ and $V$ parameters recorded on the Spectro-polarimeter (SP), and monochromatic images of the same parameters recorded on the Narrow-band Filter Imager (NFI). By applying the center-of-gravity method to the SP data of AR10930 taken on 2006 December 11, we determined the line-of-sight field at every location in the active region. As a result, we found that the line-of-sight field strength ranges up to 2 kG in plages, even without taking into account the filling factor, and up to 3.5 kG or higher values inside the umbra of the major sunspot. We calibrated the NFI data in reference to the field determined from the SP data. In regions outside the sunspots and the penumbral regions, we adopted a linear relation, $B_\Vert=\beta V/I$, between the circular polarization, $V/I$, and the line-of-sight field strength, $B_\Vert$, and obtained $\beta=$ 23.5 kG in regions outside the sunspots, and $\beta=$ 12.0 kG in penumbral regions. In umbral regions of sunspots, a first-order polynomial was adopted to model the reversal of the polarization signal over the field strength.