The Photometric Accuracy of Astronomical Images Restored with the MEMSYS3 Code

Abstract

After reviewing the causes of blur in astronomical images obtained with optical telescopes, both ground based instruments and the Hubble Space Telescope, simulations are described which test the photometric accuracy of the maximum entropy image restoration algorithm used in the code Memsys3 version 2. It is found that at the faintest brightness levels, while the code can recover blurred out point sources, they are recovered systematically too faint. The size of the photometric error depends on the brightness of the source (relative to the noise of the background) and the crowding of the field. At present, the optimum technique to apply to blurred images of crowded fields where most of the sources are point sources seems to be to use a restored image to generate the list of objects, then feed this into a standard point spread function fitting code and use this on the original blurred frame. In that manner, the most crowded fields can be analyzed without losing photometric accuracy.