Experiment on obtaining maps of solar magnetic fields with the spectrograph of the Solar Tower Telescope 2 at CrAO

Abstract

The paper describes the experiment on the solar magnetic field measurements with the spectrograph of the Solar Tower Telescope 2 (STT-2). Using a charge-coupled device (CCD), the data on solar spectra in two polarization states were collected by two consecutive scans of the solar surface. The polarization of the light beam was decoded by a quarterwave plate and a linear polarizer. The recorded spectra were processed to derive I and V Stokes profiles, which were further inverted under the Milne–Eddington atmosphere model. The method provides spatial maps of the longitudinal magnetic field component and magnetic field strength. A shortcoming of the method is the necessity to carry out two consecutive scans of the solar surface in different polarization states rather than simultaneous capturing of orthogonal polarization states using a beam splitter unit. However, the approach yielded acceptable results and showed satisfactory agreement with the data provided by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory.  We found that the polarization crosstalk of the telescope may produce false polarization signals and requires special attention.