Very Small Field Astrometry

Abstract

In contrast to the various astrometric techniques described in the preceding chapters in which focal images of stars are pointed at or analysed, it is also possible to obtain astrometric data — and actually very precise data — from treatments of the light not using images, but essentially its undulatory properties presented in Sects. 2.1.3 and 2.1.4. The methods that we are going to describe are based on interference of coherent light (see Sect. 2.3) or on diffraction (Sect 2.2) . In this first chapter, we shall present these methods in their primary application to reconstruct the image of a star or to obtain information on the structure of a light source within its immediate environment. This is the meaning we give to the expression very small field. The astrometric information that can be obtained is the apparent dimensions (diameter)of a star or the respective positions of the components of a double or multiple st ar .