Optical configuration for a micro-arcsecond astrometric interferometer in space

Abstract

One of the ESA candidate cornerstone missions is dedicated to wide-angle astrometry and aims at dramatically increasing the accuracy of astrometric measurements and the limiting magnitude with respect to Hipparcos (ESA Symposium, Venice, 1997). This mission was initially designated by the acronym GAIA (Global Astrometric Interferometer for Astrophysics) and featured several Fizeau interferometers. One important drawback of the original configuration proposed by Lindegren & Perryman (1996) was the confusion effect. This effect, which is a superposition of the light coming from different objects, is due to recording the fringe signal in the exit pupil plane of the instrument, necessary to relax the pixel size in the considered configuration. In order to overcome the confusion effect while retaining the original Fizeau interferometer concept, we present an optical configuration allowing direct fringe detection, i.e. in the image plane. It features focal length of 30 m inducing technologically feasible pixel size in the bandwidth of interest, and meets the condition to fit the Ariane V launcher fairing.