THE MPE IMAGING BEAM COMBINER SIMULATOR COSI

We present first interferograms and reconstructed images obtained with the MPE imaging beam combiner simulator COSI. The purpose of COSI is to simulate the imaging beam combiner at the coherent focus of the ESO VLTI in multi-speckle mode or under conditions of partial or full cor rection of the single telescope wave front by adaptive optics. COSI co nsists of a 1 m telescope and a near-infrared continuum light source t o simulate the radiation from astronomical objects. Two flat mirrors a llow us to use one half of the telescope as a transmitter and the othe r half as a receiver. In the receiving focus we have installed the MPE speckle camera SHARP, which uses a HgCdTe 256(2) NICMOS 3 array. A pu pil mask over the aperture allows us to simulate various telescope con figurations with a beam compression factor of 100 as it will be used f or the ESO VLT interferometer. COSI is used to explore NIR array detec tor properties and their suitability for interferometric measurements and to generate data to explore image reconstruction algorithms. First interferograms of single and multiple objects were taken early this y ear (1993). Employing various deconvolution and Fourier-inversion meth ods, a diffraction limited image of the pin-hole sources can be succes sfully recovered which experimentally demonstrates the feasibility of interferometric imaging with a beam combiner. Thus, we have demonstrat ed that COSI is an excellent test bed to investigate methods of image recovery and to investigate how the methods are influenced by effects like atmospheric turbulence, expected optical imperfections and detect or characteristics.