The nulling stellar coronagraph: Laboratory tests and performance evaluation

The nulling coronagraph, first proposed by Roddier and Roddier, uses a smal l mask (less than half the size of the central Airy spot) that shifts the p hase of the incoming light by 180 degrees to strongly attenuate the Airy sp ot as well as the rings. We report on both theoretical and laboratory perfo rmance. In our laboratory experiment, we reduce the peak intensity of the A iry pattern by a factor of 16. We derive estimates of the performance of a nulling coronagraph used on a telescope equipped with an adaptive optics sy stem, based upon the performance of the University of Hawaii Hokupa'a adapt ive optics system. On a 3.6 m telescope at 1.65 mu m, it is found that a ti p/tilt amplitude lower than 20 mas is needed for such a coronagraph to yiel d an extinction better than 2 stellar mag.