LOCATION ESTIMATORS FOR INTERFEROMETRIC FRINGES

Future global astrometry missions have targeted the determination of p ositions, parallaxes, and annual proper motions to the 10 mu as level. This can be achieved through the use of fringe imaging interferometer s, possibly featuring wide fields of view (e.g,, Fizeau configurations ). The basic location information is to be extracted from the fringe p attern by proper implementation of the detection system and proper exp loitation of the focal plane data. The sampling resolution requirement s are a key trade-off issue between science and engineering: therefore , fringe acquisition by means of realistic detectors and the resulting accuracy in photocenter location is discussed herein, The location pe rformance is described as a chi(2) minimization problem; the resulting expressions are then evaluated in analytical form and by means of a M onte Carlo simulation, which provide good agreement. In order to achie ve the limiting Interferometer accuracy, 8-10 pixels per fringe period are required, whereas a sampling resolution of 4-5 pixels per period provides a 30% degradation. We evaluate the location accuracy degradat ion induced by progressively reduced fringe visibility and increasing noise level. The former provides a smooth performance reduction, accep table to a wide extent, read-out noise is critical because the fringe pattern signal is recorded over many pixels, each providing a comparab le contribution to the overall noise.