Relative Astrometry in an Annular Field

Abstract Background. Relative astrometry at or below the microarcsec level with a 1 m class space telescope has been repeatedly proposed as tool for exo-planet detection and characterization, well several topics forefront of Astrophysics Fundamental Physics. Aim. This paper investigates potential benefits an instrument concept based on annular field view, compared to traditional focal plane imaging contiguous area close optical axis. Method. Basic aspects relative are reviewed function distribution sky reference stars brighter than G = 12 mag (from Gaia EDR3). Statistics targets down 8 is evaluated by analysis simulation. Results. Observation efficiency from prior knowledge individual targets, since source model improved few measurements. Dedicated observations (10–20 hr) can constrain orbital inclination exoplanets degrees. Observing strategy be tailored include sample stars, materialising frame, sufficiently large average residual catalog errors desired level. For most provides typically more factor four seven in our case, conventional field. The brightest each target up 2 brighter. Conclusions. improves observation flexibility and/or astrometric performance respect designs. It appears therefore appealing contribution optimization future missions.