中文摘要：

对欠采样图像做天体测量时，往往受像素相位误差的影响。利用高斯函数作为点扩散函数模型进行仿真实验表明，像素相位误差有类似正弦函数的分布，其幅度与拟合模型的半高全宽相对于星像真实的半高全宽的差别有关，拟合模型的半高全宽与星像真实的半高全宽偏差越大，像素相位误差越大。此外还对高斯与ePSF两个函数模型拟合星像位置的精度情况进行了分析。

英文摘要：

Astrometry from undersampled images is usually affected by pixel-phase errors. Using simulated images with Ganssion functions as point spread functions, we carry out a study of characteristics of pixel-phase errors. Our experimental results show that the statistical variation of pixel-phase error with pixel phase is near a sine function and the amplitude of this variation depends on the deviation of the fitting-model FWHM from true stellar FWHM. Overall the errors decrease with such deviations. In addition, we study the precisions of the fits of stellar positions by a Gaussian and an ePSF.