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8 Conclusion

In this Paper we have reported observations and results of a first test run with AIC on ground-based telescope and we have shown the interest of this type of coronagraph. In particular, we have achieved from raw data, a clear detection of a companion close to a star at an angular distance of less than the Airy angular radius and fainter than the star by $\Delta K=3.5$. This close-sensing capability has been demonstrated with the observation of 72 Peg and 5 Lac, and this capability can be enhanced by means of an appropriate post-processing of the raw data. AIC takes full advantage of the theoretical angular resolution of the telescope. Thus, it is clear that using AIC on large telescopes equipped with Adaptive Optics corrections will lead to a very-close sensing at a level better than set by the diffraction limit. With AIC the effect of the corrections by adaptive optics is to remove residual light from the coronagraphed image. The correction affects the center of the field first and gradually enlarges this "cleaned area" as the number of corrected Zernike modes is increased. This is another interest of AIC: even with a limited number of corrected modes the center of the image is "cleaned" first.
  \begin{figure}
\includegraphics[width=8cm,clip]{ds9360f11.eps}
\end{figure} Figure 11: Mean radial profiles for $\frac{D}{r_0(\mathrm{vis})}=43$. Full lines: recorded profiles with and without AIC (no selection of images). Dashed lines: simulated profiles with and without AIC. Dotted line recorded profile with AIC with substraction of the profile of a diffraction pattern weighted by RT.<d2>. Horizontal scale: arcseconds on the sky

The AIC device used for these observations was a prototype undergoing exceedingly large and fast OPD variations, which has severely limited the detection capability. For example our evaluation (Paper I) of the performance in case of uncomplete correction by AO, falls short by nearly two magnitudes with respect to the observations, and this can be explained mainly by the OPD variations. Both the size of the prototype and its sensitivity to OPD variations make it unadequate for observations on large telescopes (for which, generally speaking, only Cassegrain focus are equipped with AO). A new AIC device which is compact, has low weight and has robust OPD balance has been developed at Observatoire de la Côte d'Azur, France for observations on large telescopes. The AO system is the key point for the efficiency of AIC since working with the best wavefront is the condition required for reaching the best performance. No doubt that coupling AO and laser star will significantly increase the capabilities of AIC for ground-based observations, even though the ultimate nulling performance will be reached by installing AIC on a space-based telescope.


  \begin{figure}
\includegraphics[width=8cm,clip]{ds9360f12.eps}
\end{figure} Figure 12: Mean radial profiles for $\frac{D}{r_0(\mathrm{vis})}=52$. Full lines: recorded profiles with and without AIC (no selection of images). Dashed lines: simulated profiles with and without AIC. Dotted line recorded profile with AIC with substraction of the profile of a diffraction pattern weighted by RT.<d2>. Horizontal scale: arcseconds on the sky


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