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

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.

Progress on the Astrometric Gravitation Probe design

“…The optical design rationale and concept is described in another contribution to these Proceedings. 9 We recall that the starting point is a Three-Mirror Anastigmat (TMA), 15,16 further developed under the prescription of achieving thus fitting an envelope of ∼ 2.2 m. The optics layout is shown at the top of Fig. 5, with the corresponding spot diagram shown below.…”

“…8 In particular, a telescope especially suited to astrometry over a large annular field of view, thanks to uniform optical response, is appealing, and the concept is being investigated in detail. 9 Further author information: E-mail: mario.gai@inaf.it, Telephone: +39 011 8101 943, www.…”

The ASTRA project: a doorway to future astrometry

“…The activity is based on synergy of science and technology: we will build on our GR models for the Gaia mission, to consolidate science requirements for astrometric technology: 9, 10 measurement at < 1 µas implies simulation accuracy in the range 0.1 to 0.1 µas to ensure control of model errors. The long-term objective is the development of innovative astronomic instrumentation reliably operating in the micro-arcsecond (µas) precision range or better, also including relativistic experiments, as the above mentioned GAME/AGP, or a novel astrometric instrument concept presented in another contribution to this meeting (RAFTER, 11 ). This will be achieved through modelization, simulation and laboratory experiments, addressing some basic implementation aspects of astrometric measurements, described below.…”

“…As a possible mitigation strategy with respect to the above challenges, we investigate the concept of an annular field telescope, RAFTER: Ring Astrometric Field Telescope for Exo-planets and Relativity. 11 It features highly uniform optical response over a large focal plane area, thus providing favourable characteristics with resect to the possibility of averaging out detector and source variability over a set of observations. A specific application for Fundamental Physics, with the addition of a custom coronagraphic system, is represented by the current Astrometric Gravitation Probe design.…”

“…JWST, 13 NEAT, 14 Theia, 15 Gaia extensions to higher precision or other spectral bands, in particular NIR, 16 and others. 11,17 The main output of ASTRA will be a white paper summarising a roadmap toward future high precision astrometry.…”