P-REx: The Piston Reconstruction Experiment for infrared interferometry

• Published in: Monthly notices of the Royal Astronomical Society Vol. 475; no. 1; pp. 1224 - 1237
• Main Authors: Widmann, Felix, Pott, Jörg-Uwe, Velasco, Sergio
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 21.03.2018
• Subjects: Adaptive optics; Atmosphere; Evolution; Infrared astronomy; Interferometry; Multilayers; Reconstruction; Sky; Telescopes; Very Large Telescope; infrared: general; instrumentation: adaptive optics; instrumentation: interferometers
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stx3306

Abstract For sensitive infrared interferometry, it is crucial to control the differential piston evolution between the used telescopes. This is classically done by the use of a fringe tracker. In this work, we develop a new method to reconstruct the temporal piston variation from the atmosphere, by using real-time data from adaptive optics (AO) wavefront sensing: the Piston Reconstruction Experiment (P-REx). In order to understand the principle performance of the system in a realistic multilayer atmosphere, it is first extensively tested in simulations. The gained insights are then used to apply P-REx to real data, in order to demonstrate the benefit of using P-REx as an auxiliary system in a real interferometer. All tests show positive results, which encourages further research and eventually a real implementation. Especially, the tests on on-sky data showed that the atmosphere is, under decent observing conditions, sufficiently well structured and stable, in order to apply P-REx. It was possible to conveniently reconstruct the piston evolution in two-thirds of the data sets from good observing conditions (r0 ∼ 30 cm). The main conclusion is that applying the piston reconstruction in a real system would reduce the piston variation from around 10 μm down to 1–2 μm over time-scales of up to two seconds. This suggests an application for mid-infrared interferometry, for example for MATISSE at the very large telescope interferometer or the large binocular telescope interferometer. P-REx therefore provides the possibility to improve interferometric measurements without the need for more complex AO systems than already in regular use at 8-m-class telescopes.