Characteristics Of The Pixel-Phase Errors

As we know, astrometry for a star in an undersampled image is usually affected by pixel-phase errors. In order to solve the problem of pixel-phase error in an undersampled image taken from HST(Hubble Space Telescope), Anderson and King proposed a new fitting model, i.e., ePSF (effective point-spread function),which could derive precise centriod. However, Anderson admitted that this fitting process of ePSF is very complicated. The characteristics of pixel-phase errors were deeply studied in this thesis.In order to understand the characteristics of pixel-phase errors deeply, researches are based on a series of simulative images. In practice, We called the CFITSIO Library to produce simulative images with poisson noise.First, we introduced the concept of pixel-phase error. Secnond, we used the Gaussian to fit stars and analyzed the determination of accurate function model. Finally, we explored how the pixel-phase error affects the precision of centering. Our experimental results showed that (1) Pixel-phase errors is similar to a sine function against pixel-phase. (2) It is theoretically possible to avoid pixel-phase error as long as we can derive an accurate model of the PSF. (3) The accuracy of fitting model depends on whether the fitting model's FWHM(Full Width at Half Maximum) is equal to star's FWHM. (4) Gaussian function model, whether accurate or not, once the star's FWHM is bigger than 2 pixels, the fitting result of Gaussian would no longer surffer from pixel-phase error.