Speckle Imaging with Hypertelescopes
ABSTRACT Optical stellar interferometers have demonstrated milli-arcsecond resolution with fewapertures spaced hundreds of meters apart. To obtain rich direct images, many aper-tures will be needed, for a better sampling of the incoming wavefront. The coherentimaging thus achievable improves the sensitivity with respect to the incoherent com-bination of successive fringed exposures. Ecient use of highly diluted apertures forcoherent imaging can be done with pupil densi cation, a technique also called \hyper-telescope imaging". Although best done with adaptive phasing, concentrating mostenergy in a dominant interference peak for a rich direct image of a complex source,such imaging is also possible with random phase errors such as caused by turbulent\seeing", using methods such as speckle imaging which uses several short-exposureimages to reconstruct the true image. We have simulated such observations using anaperture which changes through the night, as naturally happens on Earth with xedgrounded mirror elements, and nd that reconstructed images of star clusters and ex-tended objects are of high quality. As part of the study we also estimated the requiredphoton levels for achieving a good signal to noise ratio using such a technique.Key words: instrumentation: high angular resolution, interferometers techniques:interferometric.