Comparison of Fitting ePSF and Fitting Gaussian-Functions

In order to solve the problem of point spread function (PSF) undersampling for the images from the Hubble Space Telescope (HST), Anderson and King proposed an effective PSF model (ePSF)with which high-precision stellar positions and fluxes can be derived through fitting. However, they applied it to ground-based images without comparing with any classical methods. We thus compare fitting ePSF to the classical fitting with Gaussian functions. We used the CFITSIO Library to simulate background images, and superimpose simulated stellar images (not undersampled) corresponding to stellar profiles of different parameters on the background images. Finally, we fit ePSF and Gaussian functions to these stellar images separately, and make the comparison for their fitting precisions. The preliminary experiments show that the precisions of the positions measured with the two algorithms are nearly identical.