Context. Exoplanet science has made staggering progress in the last two decades, due to the relentless exploration of new detection methods and refinement of existing ones. Yet astrometry offers a unique and untapped potential of discovery of habitable-zone lowmass planets around all the solar-like stars of the solar neighborhood. To fulfill this goal, astrometry must be paired with high precision calibration of the detector. Aims. We present a way to calibrate a detector for high accuracy astrometry. An experimental testbed combining an astrometric simulator and an interferometric calibration system is used to validate both the hardware needed for the calibration and the signal processing methods. The objective is an accuracy of 5 × 10 −6 pixel on the location of a Nyquist sampled polychromatic point spread function. Methods. The interferometric calibration system produced modulated Young fringes on the detector. The Young fringes were parametrized as products of time and space dependent functions, based on various pixel parameters. The minimization of function parameters was done iteratively, until convergence was obtained, revealing the pixel information needed for the calibration of astrometric measurements. Results. The calibration system yielded the pixel positions to an accuracy estimated at 4×10 −4 pixel. After including the pixel position information, an astrometric accuracy of 6 × 10 −5 pixel was obtained, for a PSF motion over more than five pixels. In the static mode (small jitter motion of less than 1 × 10 −3 pixel), a photon noise limited precision of 3 × 10 −5 pixel was reached.
The reduction of systematic effects is necessary to improve the accuracy in imaging and astrometry. For example, in Euclid Mission which aims at carrying out accurate measurements of dark energy and quantifying precisely its role in the evolution of the Universe, systematic effects need at be controlled to a level better than 10 −7 (Euclid, Science Book). To achieve this goal, a high-level of knowledge of the system point spread function (PSF) is required. This paper follows the concept-paper presented at the last SPIE conference 1 and gives the recent developments achieved in the design of the test bench for the intrapixel sensitivity measurements. The measurement technique we use is based on the projection of a high spatial resolution periodic pattern on the detector using the self-imaging property of a new class of diffractive objects named continuously self-imaging gratings (CSIG) and developed at ONERA. The principle combines the potential of global techniques, which make measurements at once on the whole FPA, and the accuracy of spot-scan-based techniques, which provide high local precision.
Theia is an astrometric mission proposed to ESA in 2014 for which one of the scientific objectives is detecting Earth-like exoplanets in the habitable zone of nearby solar-type stars. This objective requires the capability to measure stellar centroids at the precision of 1 × 10 −5 pixel. Current state-of-the-art methods for centroid estimation have reached a precision of about 3 × 10 −5 pixel at two times Nyquist sampling, this was shown at the JPL by the VESTA experiment. A metrology system was used to calibrate intra and inter pixel quantum efficiency variations in order to correct pixelation errors. The Theia consortium is operating a testbed in vacuum in order to achieve 1 × 10 −5 pixel precision for the centroid estimation. The goal is to provide a proof of concept for the precision requirement of the Theia spacecraft.The testbed consists of two main sub-systems. The first one produces pseudo stars: a blackbody source is fed into a large core fiber and lights-up a pinhole mask in the object plane, which is imaged by a mirror on the CCD. The second sub-system is the metrology, it projects young fringes on the CCD. The fringes are created by two single mode fibers facing the CCD and fixed on the mirror. In this paper we present the latest experiments conducted and the results obtained after a series of upgrades on the testbed was completed. The calibration system yielded the pixel positions to an accuracy estimated at 4 × 10 −4 pixel. After including the pixel position information, an astrometric accuracy of 6 × 10 −5 pixel was obtained, for a PSF motion over more than 5 pixels. In the static mode (small jitter motion of less than 1 × 10 −3 pixel), a photon noise limited precision of 3 × 10 −5 pixel was reached.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.