65cm Coude-Type Solar Telescope
The Solar Telescope of Okayama Astrophysical Observatory was constructed in 1968. Its primary mirror has a diameter of 65cm. The telescope mount is coude-type. The effective focal length is 37m (F/57), and the solar image at the focal plane is about 35cm in diameter. In the spectrograph room are installed a grating of 1200 grooves/mm and an Echelle grating.
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List of Publications
- References
- S. Nagasawa: 1967, "Tokyo Astronomical Observatory", Solar Phys., 2, 240
- F. Moriyama: 1975, "Tokyo Observatory Today", Sky&Telescope, 50, 276
Photographic Polarimeter
In 1956, W.Unno published a paper on the formation of spectral lines under Zeeman effect. (W. Unno: 1956, Publ. Astron. Soc. Japan, 8, 108). The theory developed in this paper (later known as Unno's formula) established the foundation of polarimetric observations, and has been widely used.
Based on Unno's theory, an instrument to measure the magnetic field on the sun (the polarimeter) was designed and tested in the 1960s, by using the Tower Telescope at Mitaka. In the 1970s, magnetic field measurements by using the photographic polarimeter equipped on the Solar Telescope at Okayama were initiated.
The polarimeter is basically an instrument to split the orthogonally polarized components in the incoming beam into two beams. Circularly polarized components are first converted into linearly polarized light by a quarter-wave plate, and then subjected to the same procedure. The output beams are led to the spectrograph, and are recorded on film. The polarimeter at Okayama uses a Rochon prism as the beam splitter, and a Fresnel rhomb as the quarter-wave retarder. The instrument is normally used at 6303 Angstrom, but Fresnel rhomb is achromatic over wide wavelength range.
The polarimeter is now stored in the observing room of the Okayama Observatory Solar Telescope. The sensitivity of the photographic observations is at most 100 gauss, so that no measurable signal is obtained outside sunspots. A photoelectric instrument which can give much higher sensitivity (the magnetograph) was completed in 1982.
