Stellar Photometry In Crowded Fields

Software available at KPNO for performing stellar photometry on digital images is summarized. Aperture sum and two dimensional fitting techniques are described and compared in terms of accuracy, versatility, and computational efficiency. Algorithms are presented for deriving the point spread function (PSF) from intensity data, and fitting it via chisquare minimization techniques to either single or multiple stellar images. The results of tests performed on artificial starfields are summarized and evaluated. Two dimensional psf fitting techniques are seen to be a versatile and accurate tool even in fairly crowded fields, though computationally quite expensive compared to aperture sum techniques.