Upgrading the GRAVITY fringe tracker for GRAVITY+: Tracking the white light fringe in the non-observable Optical Path Length state-space
M. Nowak, S. Lacour, R. Abuter, J. Woillez, R. Dembet, M. S. Bordoni, G. Bourdarot, B. Courtney-Barrer, D. Defrère, A. Drescher, F. Eisenhauer, M. Fabricius, H.… 展开作者
M. Nowak, S. Lacour, R. Abuter, J. Woillez, R. Dembet, M. S. Bordoni, G. Bourdarot, B. Courtney-Barrer, D. Defrère, A. Drescher, F. Eisenhauer, M. Fabricius, H. Feuchtgruber, R. Frahm, P. Garcia, S. Gillessen, V. Gopinath, J. Graf, S. Hoenig, L. Kreidberg, R. Laugier, J. B. Le Bouquin, D. Lutz, F. Mang, F. Millour, N. More, N. Morujão, T. Ott, T. Paumard, G. Perrin, C. Rau, D. C. Ribeiro, J. Shangguan, T. Shimizu, F. Soulez, C. Straubmeier, F. Widmann, B. Wolff
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16 pages, 8 figures. Accepted for publication in A&A
Aims. As part of the ongoing GRAVITY+ upgrade of the Very Large Telescope Interferometer infrastructure, we aim to improve the performance of the GRAVITY Fringe-Tracker, and to enable its use by other instruments. Methods. We modify the group delay controller to consistently maintain tracking in the white light fringe, characterised by a minimum group delay. Additionally, we introduce a novel approach in which fringe-tracking is performed in the non-observable Optical Path Length state-space, using a covariance-weighted Kalman filter and an auto-regressive model of the disturbance. We outline this new state-space representation, and the formalism we use to propagate the state-vector and generate the control signal. While our approach is presented specifically in the context of GRAVITY/GRAVITY+, it can easily be adapted to other instruments or interferometric facilities. Results. We successfully demonstrate phase delay tracking within a single fringe, with any spurious phase jumps detected and corrected in less than 100 ms. We also report a significant performance improvement, as evidenced by a reduction of about 30 to 40% in phase residuals, and a much better behaviour under sub-optimal atmospheric conditions. Compared to what was observed in 2019, the median residuals have decreased from 150 nm to 100 nm on the Auxiliary Telescopes and from 250 nm to 150 nm on the Unit Telescopes. Conclusions. The improved phase-delay tracking combined with whit light fringe tracking means that from now-on, the GRAVITY Fringe-Tracker can be used by other instruments operating in different wavebands. The only limitation remains the need for an optical path dispersion adjustment.
Upgrading LBTI/NOMIC with a quadruple annular groove phase mask and GeoSnap detector for imaging nearby, habitable-zone exoplanets
Steward Observatory University of Arizona（亚利桑那大学斯图尔德天文台）；Large Binocular Telescope Observatory University of Arizona（亚利桑那大学大双筒望远镜天文台）；Uppsala University（乌普萨拉大学）；Université Paris-Saclay CEA（巴黎萨克雷大学法国原子能委员会）；STAR Institute Université de Liège（列日大学STAR研究所）；KU Leuven（荷语鲁汶大学）；European Southern Observatory（欧洲南方天文台）；University of Wyoming（怀俄明大学）；Lunar and Planetary Laboratory University of Arizona（亚利桑那大学月球与行星实验室）；Arizona State University（亚利桑那州立大学）；Breakthrough Initiatives Steward Observatory University of Arizona（亚利桑那大学斯图尔德天文台突破倡议项目）；University of Eastern Finland（芬兰东部大学）；National Astronomical Observatory of Japan（日本国立天文台）；Laboratoire d’Astrophysique de Marseille（马赛天体物理学实验室）；ETH Zürich Institute for Particle Physics and Astrophysics（苏黎世联邦理工学院粒子物理与天体物理研究所）
