PLANET DETECTABILITY BY AN ADAPTIVE OPTICS STELLAR CORONAGRAPH

We show the possibilities for imaging Jupiter-like planets around nearby bright stars, assuming the availability of stellar coronagraphs coupled with modest adaptive optics mounted on large ground-based telescopes. The adaptive optics sharpens the point-spread function (PSF) of the planet, permits the use of an occulting disk smaller than the seeing disk, reduces the PSF envelope of the bright star, and therefore enhances the contrast between the planet and background. We have generated the PSF of the planet and the PSF envelope of the main star, using Monte Carlo simulations based on the Kolmogorov theory of turbulence. We calculate the signal-to-noise ratio of a model planet as a function of the angular separation based on photon statistics and realistic assumptions on the system performance. We have derived a criterion for optimizing the combination of the degree of adaptive compensation and the telescope diameter. It is found that a stellar coronagraph with modest adaptive optics mounted on a large ground-based telescope will be capable of detecting Jupiter-like planets around nearby bright stars such as alpha Cen, Sirius, and Procyon at wavelengths between 0.7 and 2.2 mum. Near-infrared observations are preferred because usable telescopes and isoplanatic angles are larger at infrared wavelengths than optical wavelengths for a given adaptive optics system. We have also found seven other target stars around which planets will be above the detection limit.