| 其他摘要 | The Lijiang 2.4m telescope is an important platform for astronomical observation in China. Pointing accuracy is one of the performance index of telescope, which affects the observation efficiency, real-time performance of the telescope, and the quality of the observation data. The pointing accuracy is affected by various factors in the design, installation operating environment. The way to improve pointing accuracy include hardware adjustment and software correction. Hardware adjustment is to reduce errors in the design installation of the telescope, and to improve the pointing accuracy by using higher-precision encoders. This method is difficult to operate and the costs is high; the software correction is to correct the pointing error in real time when the telescope observes the target by establishing a pointing error correction model to improve the pointing accuracy. This method is flexible and convenient, has a short development cycle, low cost and can significantly improve the pointing accuracy.In this paper, the method of software correction is used to correct the pointing error of the Lijiang 2.4m telescope. Based on the theory of pointing error correction, a detailed analysis of various physical factors of the telescope pointing error, including encoder zero point deviation, shaft alignment misalignment, non-orthogonality between shaft systems, lens barrel deflection, and atmosphere refraction. These errors are repeatable and can be compensated and corrected by establishing a pointing model. Commonly used pointing models are spherical harmonic function model, basic parameter model and turntable model.To establish a pointing error correction model, it is necessary to measure the pointing error throughout the day. In this paper, a grid pointing error data acquisition program is designed for the Lijiang 2.4m telescope, which can generate uniformly distributed observation targets throughout the sky. The telescope points to the target in turn, and the photometric image is taken. The image pointing information is restored by post-processing the image. This solution can effectively shorten the time of pointing error data collection, and the coordinates and time information are obtained from the TCS (Telescope Control System) as much as possible, avoiding the errors introduced by the pointing error separation experiment, and providing high quality pointing error data for subsequent modeling and analysis. In this paper, the above design scheme is used to measure the pointing error of the Lijiang 2.4m telescope. The measured results show that the telescope has a large pointing error. Then using the TPoint embedded in TCS, which is a telescope pointing analysis system, select the appropriate pointing error term, establish the initial pointing model of the Lijiang 2.4m telescope, and calculate the initial pointing model coefficient values and coefficient standard deviation after fitting. By observing the correlation coefficient matrix and residual distribution of the initial pointing model, the initial pointing model was optimized, and finally the actual pointing model of the telescope with good stability was obtained. The actual observation results after importing the final pointing model into TCS show that the pointing model has a significant correction effect on the pointing error of the telescope, the pointing accuracy of the Lijiang 2.4m telescope has been improved to a certain extent. |
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