Subjects: Astronomy >> Astrophysical processes submitted time 2023-12-06 Cooperative journals: 《天文研究与技术》
Abstract： Stellar catalogue matching is a fundamental task in astronomical observations based on CCD images. In this paper, a stellar catalogue matching algorithm based on k-d tree and k-means clustering algorithm is proposed in Python. Triangle invariant tuples are used for blind matching of similar triangles based on Astroalign, which can indirectly calculate the scale of CCD image. In this paper, k-d tree is used for three times to optimize the calculation, and k-means clustering algorithm is used to segment the image to improve the matching precision. For testing, we match the stars with both sparse field frames taken by the 1 m telescope at Yunnan Observatory and dense field frames taken by the 2. 4 m telescope at Yunnan Observatory. Our results show that the method can effectively adapt to subtle change of image scale and improve matching precision.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-10-20 Cooperative journals: 《天文研究与技术》
Abstract： Geometric distortion is a non-negligible factor for CCD high-precision measurement, which usually requires careful observational work to be derived, and inevitably takes up valuable observational time. This paper explores the change of geometric distortion with zenith distance by using the CCD image observed with the GMG -2.4 m telescope at Lijiang station. Specifically, we refer to Gaia DR3 catalog in data reduction, and correct the effect of differential color refraction (DCR). Then the geometric distortion models at different observational times are derived and are fitted with a fourth order polynomial. The results show that the geometric distortion models of the CCD frames are correlated with the zenith distance (ZD) of observational time. There are obvious linear relations between quadratic terms x4, x3 y, x2 y2, xy3, quadratic terms x2, xy and zenith distances in X coordinate; in Y coordinate, there are obvious linear relations between the quadratic terms x4, xy3, cubic term xy2, quadratic term xy of the geometric distortion models and zenith distances.
Subjects: Astronomy >> Astrophysical processes submitted time 2022-10-21 Cooperative journals: 《天文研究与技术》
Abstract： In the field of astronomical image processing, image subtraction techniques are widely used. Due to the varying seeing conditions, different exposure times, and different filters, the two images cannot do image subtraction directly. A novel image subtraction algorithm is proposed in the paper. Its essence is based on correlation to eliminate the parts with the similar flux distribution and preserve the parts with the different flux distribution between two images in sense of statistics. The algorithm can be fast executive, is numerically stable, and is locally independent. Based on our algorithm, we have developed a set of image subtraction code with Python as the interface and C as the implementation. We use the algorithm, together with three other similar algorithms, to perform with the astronomical images . Experiments show that our algorithm can find the difference between two images and detect moving objects in a very short time while having good robustness and position measurement stability.
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