VLTI Spectro Imager
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2. Instrument overview

Friday 18 January 2008

The VLTI Spectro Imager will provide the ESO community with spectrally-resolved near-infrared images at angular resolutions down to 1.1 milliarcsecond and spectral resolutions up to R=12000. Targets as faint as K=13 will be imaged without requiring a brighter nearby reference object; fainter targets can be accessed if a suitable off-axis reference is available. This unique combination of high-dynamic-range imaging at high angular resolution and high spectral resolution for a wide range of targets enables a scientific programme which will serve a broad user community within ESO and at the same time provide the opportunity for breakthroughs in many areas at the forefront of astrophysics.

A great advantage of VSI is that it will provide these new capabilities while using technologies which have extensively been tested in the past and while requiring little in terms of new infrastructure on the VLTI. At the same time, VSI will be capable to make maximum use of the new infrastructure as it becomes available. VSI provides the VLTI with an instrument capable of combining up to 8 telescopes, enabling rapid imaging through measurement of up to 28 visibilities in hundreds of wavelength channels within a few minutes. Operations with less than 8 telescopes is the scope of the first phases of VSI. Three development phases are foreseen: VSI4 combining 4 telescopes (UTs or ATs), VSI6 combining 6 telescopes (4UTS+2ATs or 4ATs+2UTS and eventually 6ATs), and perhaps ultimately, in the long-run, VSI8 combining 8 telescopes (4UTs+4ATs or eventually 8ATs). The current studies are focused on a 4-telescope version with an upgrade to a 6-telescope one. The instrument contains its own fringe tracker and wavefront control in order to reduce the constraints on the VLTI infrastructure and maximize the scientific return.

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