The effect of grid density on EPSF mode´s accuracy

Effective point-spread function (ePSF) method is an excellent method for the stars´ positional measurements in stellar images, whose critical step is constructing an accurate ePSF mode. In the study, we investigated the effect of the grid density on the mode´s accuracy by some experiments on processing synthetic stellar images in which all stars have a Gaussian PSF. Our experimental results show that the grid density significantly affects the mode´s accuracy. On the one hand, for a given full width at half maximum (FWHM) of the Gaussian PSF in one image, the finer gird leads the smaller error; on the other hand, for a given grid density, the larger FWHM brings a smaller error. Finally, a data table listed the maximum errors of the modes on different grid densities and FWHMs, from which the error level corresponding to some grid density can be looked up. The data table will benefit the application of the ePSF method in practice.