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VISIR

The mid-Infrared instrument of the ESO VLT program

	VISIR

The mid-Infrared instrument of the ESO VLT program

VISIR is the mid-infrared instrument installed in 2004 at the Cassegrain focus of MELIPAL, one of the four 8-meter telescopes of the European Very Large Telescopes program. The contract to design and build VISIR was signed in November 1996 between the European Southern Observatory (ESO) and a French-Dutch consortium of institutes led by the Astrophysics division of CEA-Dapnia. The Dutch partner is the Netherlands Foundation for Research in Astronomy (NFRA, Dwingeloo, The Netherlands).

On the left : the Paranal site (Chile) where are located the four 8-m diameter telescopes of the ESO VLT program. In the middle: one of these telescopes; on the right : VISIR mounted at the Cassegrain focus (back of the primary mirror) of 3rd telescope. (Credit ESO)

VISIR is a cryogenic instrument optimized for diffraction-limited performances in both mid-infrared atmospheric windows (N and Q bands). It combines imaging capabilities and long-slit grating spectroscopy with spectral resolutions up to R=25000 at 10 mm and 12500 at 20 mm. To set the various observing possibilities, a novel type of actuators was developed by Dapnia.

Novel cryogenic actuator developed for VISIR. The overall dimensions are as follows: outer diameter: 98 mm, inner diameter (free aperture in the shaft) : 32 mm, thickness 34.5 mm. Such a compactness was a key requirement to achieve a very compact mechanical design of the instrument.

After extensive tests in the laboratory, VISIR was shipped to Paranal in March 2004. After successful commissioning between May and August 2004 and science verification between September 2004 and January 2005, routine science operations started in April 2005. Among the various discoveries made with VISIR, we can mention the discovery of a flaring protoplanetary disk around the young star HD97048.