Jiao Tong University Spectroscopic Telescope (JUST) is a 4.8-m composite spectroscopic telescope which integrates the high-resolution observation in a small field of view (FoV) with the spectral survey in a wide FoV. The primary mirror of JUST adopts the latest segmented mirror active optics technology, which is composed of 18 hexagonal segments with a diameter of 1.1 meters each. There are two Nasmyth focal stations which can be switched by rotating the tertiary mirror. One station with a 10 arcmin FoV diameter and its image quality (full width at half maximum, FWHM) can be below 0.35 arcsec with the error budgets, which is suitable for installing high-resolution spectroscopic and imaging instruments. The other station is equipped with the wide-field correctors, which can achieve a FoV diameter of scientific 1.2 degrees and correct atmospheric dispersion. The wide-field Nasmyth focal station operates at a wavelength band ranging from 0.35 to 1.3μm and for the zenith distance ranging from 0 to 60 degrees, the image quality (FWHM) falls within a 0.75 arcsec diameter with error budgets. It is used for broad observations and mainly used for wide-field spectroscopic survey of stars, galaxies, etc. This article will describe the optical system design, the baffle design and stray light analysis, error budget, and thermal effect of the telescope in detail.
Since the publication of the HIPPARCOS catalog in 1997, and with its successor Gaia in operational phase since 2013 having already published 3 data releases, global astrometry has earned itself a prominent role in the field of astrophysics. Both missions rest on the well-established concepts of one-dimensional (or nearly one-dimensional) observations performed by a telescope that is continuously scanning the sky following a predefined scanning law. Moreover, Gaia heavily relies also on the concept of self-calibrating instrument. In this work we explore the possibility of exploiting two-dimensional observations performed by a pointed mission, discussing the feasibility of this concept, and its possible advantages.
The concept of a 3 lines of sight telescope for space astrometry is evaluated in terms of implementation feasibility and some science applications. The beam combination by pupil splitting exploits the Hipparcos concept, extending it to true large bidimensional angle. The PSF symmetry provides equivalent astrometric performance and immediate field identification on the common detector. Operation aspects are investigated in terms of field identification and observing strategy, in particular pointing constraints and sky density of reference bright stars. The approach, based on flat mirrors mounted on a pyramidal structure, provides a simple geometric framework, with immediate mechanical materialization and clear interface to metrology. The geometric arrangements considered place the lines of sight either along the (x, y, z) Cartesian axes, or in a planar layout for a Gaia-like astrometric mission. The application to a single head, multiple boresight star tracker is also outlined.
The Astrometric Gravitation Probe mission is a modern version of the 1919 Dyson-Eddington-Davidson experiment, based on a space-borne telescope with a permanent built-in eclipse, provided by a coronagraphic system. The expected improvement on experimental bounds to General Relativity and competing gravitation theories is by at least two orders of magnitude. The measurement principle is reviewed, in particular the principle of Fizeau-like combination of a set of individual inverted coronagraphs simultaneously feeding a common high resolution telescope. Also, the payload has a dual field of view property, in order to support simultaneous observations of stellar fields either very close, or far away, from the Sun, i.e. fields affected by either high or low light bending. We discuss a set of solutions introduced in the optical design to improve on technical feasibility and robustness of the optical performance against perturbations, in particular induced by manufacturing and alignment tolerances, and launch stresses.
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 that 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.
Astrometric Science and Technology Roadmap for Astrophysics (ASTRA) is a bilateral cooperation between China and Italy with the goal of consolidating astrometric measurement concepts and technologies. In particular, the objectives include critical analysis of the Gaia methodology and performance, as well as principle demonstration experiments aimed at future innovative astrometric applications requiring high precision over large angular separations (one to 180 degrees). Such measurement technologies will be the building blocks for future instrumentation focused on the "great questions" of modern cosmology, like General Relativity validity (including Dark Matter and Dark Energy behavior), formation and evolution of structure like proto-galaxies, and planetary systems formation in bio compatibles environments. We describe three principle demonstration tests designed to address some of the potential showstoppers for high astrometric precision experiments. The three tests are focused on the key concepts of multiple fields telescopes, astrometric metrology and very fine sub-pixel precision (goal: < 1/2000 pixel) in white light.
Ground based optical observation is widely used in the field of astrometry of moving objects such as Near-Earth Objects and space debris due to its low cost and easy deployment. However, it’s difficult for traditional optical telescopes to have both large aperture and wide FOV, making it impossible to achieve both observation depth and observation efficiency. We propose the computational imaging astrometry method to solve this problem. Based on a scientific CMOS detector and a small-aperture telescope with wide FOV, through strict correction of various astronomical effects and instrumental errors, we establish a high-precision overlay enhancement method for wide-FOV astronomic images. Including displacement overlay of high frame rate images at sub-pixel scale. In the case of no mechanical tracking device, the computational imaging astrometry method enables the observation system to simultaneously track multiple types of moving objects, and exert the ability of image overlay to reduce background noise, thus improving the SNR of the target and enhancing the observation depth of the system.
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