12 September 2012 The GRAVITY spectrometers: optical design
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Operating on 6 interferometric baselines, i.e. using all 4 unit telescopes (UTs) of the Very Large Telescope Interferometer (VLTI) simultaneously, the 2nd generation VLTI instrument GRAVITY will deliver narrow-angle astrometry with 10μas accuracy at the infrared K-band. At this angular resolution, GRAVITY will be able to detect the positional shift of the photo-center of a flare at the Galactic Center within its orbital timescale of about 20 minutes, using the observed motion of the flares as dynamical probes of the gravitational field around the supermassive black hole Sgr A*. Within the international GRAVITY consortium, the 1. Physikalische Institut of the University of Cologne is responsible for the development and construction of the two spectrometers of the camera system: one for the science object, and one for the fringe tracking object, both being operated at cryo-vacuum. In this paper we present the phase-C final optical design of the two spectrometers as it got derived from the scientific and technical requirements and as it was presented and reviewed successfully at the Final Design Review (FDR) at the European Southern Observatory (ESO) in October 2011.
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Christian Straubmeier, Sebastian Fischer, Constanza Araujo-Hauck, Michael Wiest, Senol Yazici, Imke Wank, Frank Eisenhauer, Guy Perrin, Wolfgang Brandner, Karine Perraut, António Amorim, Markus Schöller, and Andreas Eckart "The GRAVITY spectrometers: optical design", Proc. SPIE 8445, Optical and Infrared Interferometry III, 84452R (12 September 2012); doi: 10.1117/12.925129; https://doi.org/10.1117/12.925129

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