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Digitizer of astronomical plates at Shanghai Astronomical Observatory and its performance test

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Research in Astronomy and Astrophysics 2017年第3期17卷 67-76页

作者： Yong Yu Jian-Hai Zhao Zheng-Hong Tang Zheng-Jun Shang Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai 200030 China

Before CCD detectors were widely employed in observational astronomy, the main method of detection was the use of glass astrophotographic plates. Astronomical plates have been used to record information on the position and activity of celestial bodies for more than 100 years. There are about 30 000 astronomical plates in China, and the digitization of astronomical plates is of great significance for permanent preservation and to make full use of these valuable observation data. A digitizer with high precision and high measuring speed is a key piece of equipment for carrying out the task of dig- itizing these astronomical plates. A digitizer for glass astrophotographic plates was developed jointly by Shanghai Astronomical Observatory and Nishimura Co., Ltd of Japan. The digitizer＇s hardware was manufactured by Nishimura Co., Ltd, and the performance test, error corrections as well as image pro- cessing of the digitizer were carried out by Shanghai Astronomical Observatory. The main structure and working mode of the digitizer are introduced in this paper. A performance test shows that brightness uniformity of illumination within the measuring area is better than 0.15%, the repeatability of digitized positions is better than 0.2 μm and the repeatability of digitized brightness is better than 0.01 instrumen- tal magnitude. The systematic factors affecting digitized positions, such as lens distortion, the actual optical resolution, non-linearity of guide rails, non-uniformity of linear motors in the mobile platform, deviation of the image mosaic, and non-orthogonality between the direction of scanning and camera lin- ear array, are calibrated and evaluated. Based on an astronomical plate with a size of 300 mm × 300 mm, which was digitized at different angles, the conversion residuals of positions of common stars on dif- ferent images were investigated. The results show that the standard deviations of the residuals are better than 0.9μm and the residual distribution is al

关键词： astrometry - instrumentation detectors - methods data analysis - techniques imageprocessing

Automated spectral classification using template matching

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Chinese Journal of Astronomy and Astrophysics 2009年第3期9卷 341-348页

作者： Fu-Qing Duan Rong Liu Ping Guo Ming-Quan Zhou Fu-Chao Wu College of Information Science and Technology Beijing Normal University Beijing 100875 China Base Department Beijing Institute of Clothing Technology Beijing 100029 China National Laboratory of Pattern Recognition Institute of Automation Chinese Academy of SciencesBeijing 100080 China

An automated spectral classification technique for large sky surveys is proposed. We firstly perform spectral line matching to determine redshift candidates for an observed spectrum, and then estimate the spectral class by measuring the similarity between the observed spectrum and the shifted templates for each redshift candidate. As a byproduct of this approach, the spectral redshift can also be obtained with high accuracy. Compared with some approaches based on computerized learning methods in the literature, the proposed approach needs no training, which is time-consuming and sensitive to selection of the training set. Both simulated data and observed spectra are used to test the approach; the results show that the proposed method is efficient, and it can achieve a correct classification rate as high as 92.9%, 97.9% and 98.8% for stars, galaxies and quasars, respectively.

关键词： methods data analysis - techniques spectroscopic - stars general - galaxies stellar.content

Optical fiber positioning based on four-quadrant detector with Gaussian fitting method

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Research in Astronomy and Astrophysics 2017年第7期17卷 115-120页

作者： Jin-Sheng Liu Hua Zou Mei-Ling Zhang Lin-Zheng Wang College of Science Hohai University

With the development of large-scale spectral surveys, fiber positioning technology has been developing rapidly. Because of the performance advantages of a four-quadrant（4Q） detector, a fiber positioning and real-time monitoring system based on the 4Q detector is proposed. The detection accuracy of this system is directly determined by the precision of the center of the spot. A Gaussian fitting algorithm based on the 4Q detector is studied and applied in the fiber positioning process to improve the calculated accuracy of the spot center. The relationship between the center position of the incident spot and the detector output signal is deduced. An experimental platform is built to complete the simulated experiment. Then we use the Gaussian fitting method to process experimental data, compare the fitting value with the theoretical one and calculate the corresponding error.

关键词： instrumentation detectors - methods data analysis - techniques imaging spectroscopy- telescopes