25 October 2004 Interferometric fringes with MACAO-VLTI corrected starlight and VINCI
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We report on observations with MACAO-VLTI to feed the VLT Interferometer in November 2003. The purpose of this observing run was to optimize the feed to the VLTI by varying certain parameters of the curvature AO system and of the interferometer instrument VINCI. All along the main concern about this instrument combination was the differential piston introduced by 2 independent AO systems. A special so-called “piston removal algorithm” has been developed especially for this purpose. Each DM Influence Function is carefully characterized and a pure piston mode is defined to compensate piston over the pupil produced by a given voltage set. Piston is reduced by ~20 using this algorithm. It was found that decreasing the system main gain, while reducing strehl ratio, also reduces high frequency vibrations on the DM and therefore OPD variations. A control frequency of 420 Hz instead of the nominal 350 Hz was found to improve substantially the coupling by reducing the excitation of the DM resonance (~700Hz). On bright stars, an improvement of a factor of 30 in the flux injection into the VINCI fibers was measured. Following these tests a successful observation of the active nucleus of NGC 1068 was performed leading to a visibility of 40.4±5.4% on an average baseline of 45.84 m. The K magnitude in the 60 mas central source is 9.2±0.4. The results already put some interesting constraints on the inner torus and central engine of the nucleus of NGC 1068 but mostly show that the combination MACAO-VLTI and VINCI opens the realm of extragalactic astronomy to interferometry.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Robin Arsenault, Pierre Kervella, Rob Donaldson, Markus Erdmann Kasper, Enrico Fedrigo, Anders Wallander, Markus Schoeller, Nico Housen, Francoise Delplancke, Fernando Salgado, Christophe Dupuy, Norbert N. Hubin, Liviu Ivanescu, Sylvain Oberti, Jerome Paufique, Silvio Rossi, Markus Wittkowski, "Interferometric fringes with MACAO-VLTI corrected starlight and VINCI", Proc. SPIE 5490, Advancements in Adaptive Optics, (25 October 2004); doi: 10.1117/12.552574; https://doi.org/10.1117/12.552574

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