PIONIER: A Four-telescope Instrument for the VLTI

The Messenger 146 – December 2011 wavelength channel and one closure amplitude, whereas a three-telescope combiner only provides three visibilities and one closure phase. The remarkable success of the four-telescope (4T) CHARA inter ferometer ( Monnier et al., 2007) has demonstrated that such an increase in uv-plane coverage significantly improves the capability to reconstruct a “modelindependent” image from the observables, so-called aperture synthesis imaging.