The development of filter vector magnetographs for the Solar Magnetic Activity Research Telescope (SMART)

Abstract

In recent years, it is beginning to be shown observationally and theoretically that the existence of the magnetic field is indispensable for active phenomena on the solar surface. In particular, the rotation or helicity of the magnetic field and their temporal variation are considered to be important factors which influence solar activity. In order to confirm this, it is necessary to compute vector components of the magnetic field with a higher accuracy than before. Therefore, we developed two kinds of filter-type magnetographs for the Solar Magnetic Activity Research Telescope (SMART) at Hida observatory, which allow us to observe the polarization components in sunlight with high accuracy. We use a Lyot filter in one of two sets of magnetographs. On the other hand, a tandem-typed Fabry-Perot filter is used in one more set. For these two instruments, we made the following concrete advances. 1. The method of coating of the pre-filters. 2. Special fine-anneal on the main lenses. 3. Highly accurate rotating wave-plate. 4. Simultaneous observation of two kinds of filtergrams which have orthogonally polarized light mutually by using Fabry-Perot channel. 5. Observation in four wavelengths which can suppress various errors. 6. Low apparent Doppler shift in the FOV due to the oblique incidence of the rays to the filters. 7. Large format CCD (large-sized chip, large full-well). 8. High speed data transfer interface between the CCD and PC. In this paper, we report the details of these points, the expected effect of them, and the results of initial measurements.