System overview of the VLTI Spectro-Imager

TL;DR

The VLTI Spectro Imager project aims to enable high-resolution astronomical imaging by combining multiple beams with advanced spectral capabilities, using a comprehensive system of subsystems for data collection, calibration, and control.

Contribution

This paper presents the overall system design and concept of the VSI, including its subsystems, integrated optics beam combiners, and performance considerations.

Findings

Design of a six-subsystem VSI architecture

Implementation of integrated optics multi-way beam combiners

Performance budget analysis for the VSI instrument

Abstract

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.