The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and with a maximum
angular resolution of 1 milliarcsecond, making best use of the Very Large Telescope Interferometer capabilities. To
fulfill the scientific goals (see Garcia et. al.), the system requirements are: a) combining 4 to 6 beams; b) working in
spectral bands J, H and K; c) spectral resolution from R= 100 to 12000; and d) internal fringe tracking on-axis, or off-axis
when associated to the PRIMA dual-beam facility.
The concept of VSI consists on 6 sub-systems: a common path distributing the light between the fringe tracker and the
scientific instrument, the fringe tracker ensuring the co-phasing of the array, the scientific instrument delivering the
interferometric observables and a calibration tool providing sources for internal alignment and interferometric
calibrations. The two remaining sub-systems are the control system and the observation support software dedicated to the
reduction of the interferometric data.
This paper presents the global concept of VSI science path including the common path, the scientific instrument and the
calibration tool. The scientific combination using a set of integrated optics multi-way beam combiners to provide high-stability
visibility and closure phase measurements are also described. Finally we will address the performance budget of
the global VSI instrument. The fringe tracker and scientific spectrograph will be shortly described.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.