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21 February 2003 Fizeau beam-combination for optical astronomy: piston retrieval
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The field of view for the first generation VLTI instruments (VINCI, MIDI, AMBER etc.) is limited to the diffraction limited beam of a single telescope (for a 8.2-meter telescope at 2-micron this is 0.6 arcseconds). However, the VLTI infrastructure with its main delay lines, transfers a 2 arcseconds beam from the telescopes to the interferometric laboratory. When we discuss wide field imaging in the context of this paper, we refer to these 2 arcseconds. Although most current optical interferometers use Michelson pupil plane beam-combination there is a convincing scientific justification for wider field imaging capabilities to allow astrometry, photometry and ultimately spectroscopy of crowded fields (e.g. galactic center, globular clusters), binaries, stellar disks and dust shells. In this paper we present a newly developed tool to model a fringe tracker for a Fizeau interferometer by retrieving the piston of each individual telescope from the combined point spread function. This study shows that the pistons can be retrieved. Detecting the signal in at least two wavelength channels with an energy sensitive detector (e.g. Superconducting Tunneling Junction) allows compensation for the atmospheric piston and successively coherent integration of a science channel. The examples provided in this paper are compliant with the VLTI infrastructure and are part of a larger project to study the feasibility of a wide field imager for the VLTI as a third generation instrument. Finally we present a conceptional design for a wide field imaging for the VLTI, referred to as VLTI-WIDY.
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Eric J. Bakker and Rudolf S. Le Poole "Fizeau beam-combination for optical astronomy: piston retrieval", Proc. SPIE 4838, Interferometry for Optical Astronomy II, (21 February 2003);


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