Characteristics of Pixel-Phase Errors

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.