12 September 2012 First faint dual-field phase-referenced observations on the Keck interferometer
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Ground-baseed long baselinne interferomeeters have lonng been limiteed in sensitiviity by the shoort integration periods imposed by atmospheric tuurbulence. Thee first observaation fainter thhan this limit wwas performedd on January 222, 2011 when the Keck Interferommeter observedd a K=11.5 taarget, about onne magnitude fainter than iits K=10.3 limmit. This observation wwas made posssible by the Duual Field Phase Referencing instrument of the ASTRA pproject: simultaaneously measuring thhe real-time efffects of the atmmosphere on a nearby bright guide star, andd correcting foor it on the fainnt target, integration tiime longer thaan the turbulennce time scale are made possible. As a preelude to this ddemonstration, we first present the implementatioon of Dual FField Phase RReferencing onn the interferoometer. We tthen detail itss on-sky performance focusing on tthe accuracy oof the turbulennce correction, and on the reesulting fringe contrast stabiility. We conclude witth a presentatioon of early resuults obtained wwith Laser Guidde Star AO andd the interferommeter.
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J. Woillez, P. Wizinowich, R Akeson, M . Colavita, J. Eisner, R. Millan-Gabet, J. Monnier, J.-U. Pott, S. Ragland, E. Appleby, A. Cooper, C. Felizardo, J. Herstein, O. Martin, D. Medeiros, D. Morrison, T. Panteleeva, B. Smith, K. Summers, K. Tsubota, C. Tyau, and E. Wetherell "First faint dual-field phase-referenced observations on the Keck interferometer", Proc. SPIE 8445, Optical and Infrared Interferometry III, 84450E (12 September 2012); doi: 10.1117/12.926404; https://doi.org/10.1117/12.926404

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