RAFTER: Ring Astrometric Field Telescope for Exo-planets and Relativity

TL;DR

RAFTER is a compact 1-meter class telescope designed for high-precision astrometry, featuring an innovative optical system with a large diffraction-limited field of view suitable for exoplanet and relativity studies.

Contribution

It introduces a novel TMA-based optical design with high filling factor for an annular FOV, improving calibration and response stability for astrometric measurements.

Findings

Diffraction limited FOV exceeds 1.25 square degrees

Detector covers 0.25 square degrees with 66 devices

Design is compatible with modern CCD and CMOS detectors

Abstract

High precision astrometry aims at source position determination to a very small fraction of the diffraction image size, in high SNR regime. One of the key limitations to such goal is the optical response variation of the telescope over a sizeable FOV, required to ensure bright reference objects to any selected target. The issue translates into severe calibration constraints, and/or the need for complex telescope and focal plane metrology. We propose an innovative system approach derived from the established TMA telescope concept, extended to achieve high filling factor of an annular field of view around the optical axis of the telescope. The proposed design is a very compact, 1 m class telescope compatible with modern CCD and CMOS detectors (EFL = 15 m). We describe the concept implementation guidelines and the optical performance of the current optical design. The diffraction limited FOV exceeds 1.25 square degrees, and the detector occupies the best 0.25 square degree with 66 devices.