Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
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DEVELOPMENT OF THE SNU COELOSTAT: CONCEPTUAL DESIGN

  • Kang, Juhyung (Department of Physics and Astronomy, Seoul National University) ;
  • Chae, Jongchul (Department of Physics and Astronomy, Seoul National University) ;
  • Kwak, Hannah (Department of Physics and Astronomy, Seoul National University) ;
  • Yang, Heesu (Korea Astronomy and Space Science Institute)
  • Received : 2018.10.10
  • Accepted : 2018.12.12
  • Published : 2018.12.31
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Abstract

A coelostat is often used for solar observations, because it corrects the image rotation automatically by guiding sunlight into a fixed telescope with two plane mirrors. For the purposes of education and spectroscopic observation, the solar group at Seoul National University (SNU) plans to develop the SNU coelostat (SNUC) and install it in the SNU Astronomical Observatory (SAO). Requirements of the SNUC are < 1" positioning accuracy with 30 cm beam size on the entrance pupil in the compact dome. To allow for installation in the small dome, we design a compact slope type coelostat with a 45 cm primary plane mirror and a 39 cm secondary plane mirror. The motion of the SNUC is minimized by fixing the position of the slope frame. Numerical simulations of the available observational time of the designed coelostat shows that the sun can be observed ay all times from June to early August and at least three hours in other months. Since the high accuracy driving motors installed in the SNUC can be affected by external environment factors such as humidity and temperature variations, we design a prototype to test the significance of these effects. The prototype consists of a 20 cm primary plane mirror, a 1 m slope rail, a direct drive motor, a ballscrew, a linear motion guide, an AC servo motor, a reduction gear and a linear encoder. We plan to control and test the accuracy of the prototype with varying atmospheric conditions in early 2019. After testing the prototype, the SNUC will be manufactured and installed in SAO by 2020.

Keywords

CMHHBA_2018_v51n6_207_f0001.tif 이미지

Figure 1. The reconstructed SAO. The large dome located to the right is for night observations and includes the 1 m reflective telescope. The left dome is the solar dome, where the coelostat will be installed.

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Figure 2. Schematic illustration of the solar dome and labo-ratory. Units of lengths are mm. The solar dome is shown in black line. The red (blue) ellipse represents the PM (SM) and the orange lines are the light path of the sunlight. The simplified optics are shown in the red dashed box.

CMHHBA_2018_v51n6_207_f0003.tif 이미지

Figure 3. The 3-dimensional conceptual design of the SNUC. The blue and red circles represent the PF and SF respec-tively. The orange line is the lightpath, and the green line is the path of PF on the slope which is represented in purple. All relevant vectors and parameters are shown in this figure.

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Figure 4. The conceptual design of the SNUC for four different times. The panels from (a) to (c) show the rotation of PF at different times during a day in the summer. The panel (d) represents the positions of PF and SF during the winter season.

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Figure 5. The observable time diagram for SNUC in the solar dome at the SAO. The white represents the available time to observe the sun, but the sunlight is blocked in the blue region.

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Figure 6. Prototype design of the primary part of the SNUC.

Table 1 Information on the solar observational facilities

CMHHBA_2018_v51n6_207_t0001.tif 이미지

Table 2The requirements of the SNUC

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Table 3 Parameters of conceptual design of the SNUC

CMHHBA_2018_v51n6_207_t0003.tif 이미지

Table 4 Parameters of the PSNUC

CMHHBA_2018_v51n6_207_t0004.tif 이미지

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