Knox-Thompson Imaging at Low Light Levels

Abstract

Speckle interferometry is proving to be an important tool for astronomical research, allowing measurements of a wide range of scientifically interesting objects that can be made in no other way. Most speckle scientific results to date have been on sources which are bright and have relatively simple geometries These results include the determination of close binary star orbits and the measurement of stellar angular diameters. Many astronomical problems require the study of faint, complex, extended sources. At the Center for Astrophysics (CfA), we have been developing detectors and algorithms for this application. The Knox-Thompson (K-T) algorithm (Knox, 1976) is one of a class of approaches which preserves the phase in the speckle process, allowing true image reconstruction. K-T has proven to be a robust and accurate approach to phase recovery, due to several improvements in the technique since Knox's original implementation. These improvements include the averaging of complex vector differences rather than phase differences and the application of a least squares error distribution in the phase estimation process.