High precision differential astrometry

Differential astrometry measures the position and motion of celestial objects relative to nearby stars. Missions like Hipparcos and Gaia reached microarcsecond precision, and future missions such as NASA’s HWO and ESA’s Theia aim for sub-microarcsecond accuracy, enabling studies of Galactic dark matter and the detection of Earth-mass exoplanets. This work presents key elements of a high-precision astrometric instrument and the simulations of the calibrations required to reach this accuracy. We characterize the 46Mpx Gigapyx CMOS detector from Pyxalis, showing its strong potential for future astrometric focal planes. Sub-microarcsecond precision corresponds to 10⁻⁵ (HWO) or 10⁻⁶ (Theia) pixels on the detector. It requires micro-pixel mapping of gigapixel-scale detectors and optical distortion calibration thanks to high-order polynomial models. We introduce the IPAG (Grenoble) testbed enabling these measurements.