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Proceedings Paper

VISIR upgrade overview: all's well that ends well
Author(s): Florian Kerber; Hans Ulrich Käufl; Konrad Tristram; Daniel Asmus; Pedro Baksai; Nicola Di Lieto; Danuta Dobrzycka; Philippe Duhoux; Gert Finger; Christian Hummel; Derek Ives; Gerd Jakob; Lars Lundin; Dimitri Mawet; Leander Mehrgan; Eric Pantin; Miguel Riquelme; Joel Sanchez; Stefan Sandrock; Ralf Siebenmorgen; Jörg Stegmeier; Alain Smette; Julian Taylor; Mario van den Ancker; Guillermo Valdes; Lars Venema
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Paper Abstract

We present an overview of the VISIR instrument after its upgrade and return to science operations. VISIR is the midinfrared imager and spectrograph at ESO’s VLT. The project team is comprised of ESO staff and members of the original VISIR consortium: CEA Saclay and ASTRON. The project plan was based on input from the ESO user community with the goal of enhancing the scientific performance and efficiency of VISIR by a combination of measures: installation of improved hardware, optimization of instrument operations and software support. The cornerstone of the upgrade is the 1k by 1k Si:As AQUARIUS detector array manufactured by Raytheon. In addition, a new prism spectroscopic mode covers the whole N-band in a single observation. Finally, new scientific capabilities for high resolution and high-contrast imaging are offered by sub-aperture mask and coronagraphic modes. In order to make optimal use of favourable atmospheric conditions, a water vapour monitor has been deployed on Paranal, allowing for real-time decisions and the introduction of a user-defined constraint on water vapour. During the commissioning in 2012, it was found that the on-sky sensitivity of the AQUARIUS detector was significantly below expectations. Extensive testing of the detector arrays in the laboratory and on-sky enabled us to diagnose the cause for the shortcoming of the detector as excess low frequency noise. It is inherent to the design chosen for this detector and cannot be remedied by changing the detector set-up. Since this is a form of correlated noise, its impact can be limited by modulating the scene recorded by the detector. After careful analysis, we have implemented fast (up to 4 Hz) chopping with field stabilization using the secondary mirror of the VLT. During commissioning, the upgraded VISIR has been confirmed to be more sensitive than the old instrument, and in particular for low-resolution spectroscopy in the N-band, a gain of a factor 6 is realized in observing efficiency. After overcoming several additional technical problems, VISIR is back in Science Operations since April 2015. In addition an upgrade of the IT infrastructure related to VISIR has been conducted in order to support burst-mode operations. Science Verification of the new modes was performed in Feb 2016. The upgraded VISIR is a powerful instrument providing close to background limited performance for diffraction-limited observations at an 8-m telescope. It offers synergies with facilities such as ALMA, JWST, VLTI and SOFIA, while a wealth of targets is available from survey works like WISE. In addition, it will bring confirmation of the technical readiness and scientific value of several aspects for future mid-IR instrumentation at Extremely Large Telescopes. We also present several lessons learned during the project.

Paper Details

Date Published: 3 August 2016
PDF: 13 pages
Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 99080D (3 August 2016); doi: 10.1117/12.2232441
Show Author Affiliations
Florian Kerber, European Southern Observatory (Germany)
Hans Ulrich Käufl, European Southern Observatory (Germany)
Konrad Tristram, European Southern Observatory (Chile)
Daniel Asmus, European Southern Observatory (Chile)
Pedro Baksai, European Southern Observatory (Chile)
Nicola Di Lieto, European Southern Observatory (Germany)
Danuta Dobrzycka, European Southern Observatory (Germany)
Philippe Duhoux, European Southern Observatory (Chile)
Gert Finger, European Southern Observatory (Germany)
Christian Hummel, European Southern Observatory (Germany)
Derek Ives, European Southern Observatory (Germany)
Gerd Jakob, European Southern Observatory (Germany)
Lars Lundin, European Southern Observatory (Germany)
Dimitri Mawet, Jet Propulsion Lab. (United States)
Leander Mehrgan, European Southern Observatory (Germany)
Eric Pantin, CEA-Ctr. de SACLAY (France)
Miguel Riquelme, European Southern Observatory (Chile)
Joel Sanchez, Max-Planck-Institut für Astronomie (Germany)
Stefan Sandrock, European Southern Observatory (Germany)
Ralf Siebenmorgen, European Southern Observatory (Germany)
Jörg Stegmeier, European Southern Observatory (Germany)
Alain Smette, European Southern Observatory (Chile)
Julian Taylor, European Southern Observatory (Germany)
Mario van den Ancker, European Southern Observatory (Germany)
Guillermo Valdes, European Southern Observatory (Chile)
Lars Venema, ASTRON (Netherlands)

Published in SPIE Proceedings Vol. 9908:
Ground-based and Airborne Instrumentation for Astronomy VI
Christopher J. Evans; Luc Simard; Hideki Takami, Editor(s)

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