CLOSURE-PHASE IMAGING WITH PARTIAL ADAPTIVE CORRECTION

We explore the effects of localized adaptive wave front correction on the performance of closure-phase (nonredundant mask, NRM) imaging. Specifically, we examine a system in which tip-tilt corrections are applied to individual beams transmitted by a mask in the telescope pupil plane. Piston errors between the beams are not corrected. Using numerical simulations we have investigated the optimization of the subaperture size and science detector integration time as a function of the seeing parameters for high and low light levels. Our calculations predict improvements in the signal-to-noise ratios of monochromatic power spectrum and bispectrum measurements by factors in the range 2-15 over their uncorrected values. For a given number of adaptive degrees of freedom, this type of sparse and localized adaptive correction is far more efficient in terms of improving the performance of NRM imaging than conventional low-order modal correction when applied to large optical telescopes. The simple AO system we examine represents a cost-effective method for extending the utility of closure-phase imaging using a very small number of active optical components. Suitable astrophysical sources amenable to such an approach include evolved supergiant stars, long period variables, and other bright compact objects.