Two-dimensional aperture photometry - Signal-to-noise ratio of point-source observations and optimal data-extraction techniques

Abstract

New methodology and associated software techniques for use when performing two-dimensional aperture photometry with data from areal detectors are presented. It is shown that applying simple Poisson statistics to point sources only works in certain limited regimes and that for many situations the 'CCD equation' must be employed to get accurate results. Sky or background subtraction is again found to be of critical importance and, of five background estimation methods tried, each had some difficulties in producing a 'correct' background value. CCD growth curves are introduced as a means of correcting the flux from faint or crowded sources, when measured with very small (optimum) apertures. These optimum apertures are of interest as they are shown to give large increases in S/N for point-source observations. The usage of these small apertures along with CCD growth curves is discussed and presented with emphasis on their use for time-resolved CCD photometry.