VEGA: A Visible Spectrograph and Polarimeter for the VLTI

The ESO/VLTI has now clearly a position of world leader in the domain of ground-based optical interferometry. With four 8.2 m telescopes and two (four) 1.8 m telescopes, the Paranal Observatory is without any doubt the best optical interferometric facility in the world. Since many years, it has attracted the major part of the European interferometric community and with the opening of MIDI and AMBER, the astronomers have now access to ’general user’ interferometric instruments in the thermal and near infrared. This paper describes a project for a second generation focal instrument of the VLTI, named VEGAfor Visible spEctroGraph and polArimeter. The goal is to give access to the visible wavelength region, with spectroscopic and polarimetric capabilities, taking advantage of the coherent field of view of the VLTI. It is a unique scientific field for the VLTI. For example, a 200m interferometer operating in the visible will be able to resolve structures of the order of 0.5 mas or 0.1 AU at the distance of the Ophiuchus cloud.