We report the first near-IR polar-interferometric observations, performed at the IOTA array using its integrated
optics combiner IONIC. Fringes have been obtained on calibration stars and resolved late-type giants. Optical
modeling of the array and dedicated laboratory measures allowed us to confirm the good accuracy obtained on
the calibrated polarized visibilities and closure phases. However, no evidences for polarimetric features at high
angular resolution have been detected. The simulations and the results presented here open several perspectives
for polar-interferometry, especially in the context of fibered, single-mode combiners.
Two of the three instruments proposed to ESO for the second generation instrumentation of the VLTI would
use integrated optics for beam combination. Several design are studied, including co-axial and multi-axial
recombination. An extensive quantity of combiners are therefore under test in our laboratories. We will present
the various components, and the method used to validate and compare the different combiners. Finally, we will
discuss the performances and their implication for both VSI and Gravity VLTI instruments.
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.
The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer
providing 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 reference is
available. The unique combination of high-dynamic-range imaging at high angular resolution and high spectral
resolution enables a scientific program which serves a broad user community and at the same time provides the
opportunity for breakthroughs in many areas of astrophysics. The high level specifications of the instrument are
derived from a detailed science case based on the capability to obtain, for the first time, milliarcsecond-resolution
images of a wide range of targets including: probing the initial conditions for planet formation in the AU-scale
environments of young stars; imaging convective cells and other phenomena on the surfaces of stars; mapping
the chemical and physical environments of evolved stars, stellar remnants, and stellar winds; and disentangling the central regions of active galactic nuclei and supermassive black holes. VSI will provide these new capabilities
using technologies which have been extensively tested in the past and VSI requires little in terms of new
infrastructure on the VLTI. At the same time, VSI will be able to make maximum use of new infrastructure as it
becomes available; for example, by combining 4, 6 and eventually 8 telescopes, enabling rapid imaging through
the measurement of up to 28 visibilities in every wavelength channel within a few minutes. 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 tip-tilt control in order to reduce the constraints on the VLTI infrastructure and maximize
the scientific return.
VLTi Spectro-Imager (VSI) is a proposition for a second generation VLTI instrument which is aimed at providing
the ESO community with the capability of performing image synthesis at milli-arcsecond angular resolution. VSI
provides the VLTI with an instrument able to combine 4 telescopes in a baseline version and optionally up to
6 telescopes in the near-infrared spectral domain with moderate to high spectral resolution. The instrument
contains its own fringe tracker in order to relax the constraints onto the VLTI infrastructure. VSI will do
imaging at the milli-arcsecond scale with spectral resolution of: a) the close environments of young stars probing
the initial conditions for planet formation; b) the surfaces of stars; c) the environment of evolved stars, stellar
remnants and stellar winds, and d) the central region of active galactic nuclei and supermassive black holes. The
science cases allowed us to specify the astrophysical requirements of the instrument and to define the necessary
studies of the science group for phase A.