Preliminary Exploration of the Change of Geometric Distortion of the 2.4m Telescope at Yunnan Observatories

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, x³y, x²y², 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.