Conclusion

We have shown the feasability of imaging binary systems with the dark-speckle coronagraph, up to difference magnitudes of 4 and despite acquisition problems. Longer integrations will be required to achieve the maximum ratio predicted by the dark-speckle model (see section 3.1). Our results on $\delta$ Per and $\eta$ Psc were affected by the presence of static optical defects mostly due to the pupil stop and to the AO system, which limits the speckle smoothing. The fixed residual speckles remain the dominant source of noise in these coronagraphic data and should be removed from future systems. If the phase distribution in the detected speckled coronagraphic image could be recorded, the fixed contribution could in principle be attenuated by adaptive optics, as shown by Malbet et al. (1995).
Our preliminary results cannot yet indicate whether extra-solar planets will be actually observable with ground-based telescopes, as suggested by the theoritical analysis (Boccaletti et al. 1998). The situation is much more favourable in space, where the dark speckles can be "boiled" leisurely, using one or ten second cycles of actuator switching and exposing. Following 8m orbital telescopes, large interferometric arrays of free-flying telescopes will also be usable for coronographic dark speckle imaging (Labeyrie 1998). We are grateful to the Office National
d'Etudes et de Recherches Aérospatiales for providing their adaptive optics system. We thank Jean Gay, Yves Rabbia and Pierre Baudoz for a convivial sharing of the telescope light, and to the staff at the Observatoire de Haute-Provence for their efficient support.