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1 Introduction

The difficulty of observing faint emissions in the close environment of bright objects like stars led astronomers to develop stellar coronagraphs. In the mid 1980's, coronagraphic masks placed in focal plane of ground based telescopes allow decreasing the flux ratio between the star and its close vicinity (see for example: Smith & Terrile 1984; Paresce et al. 1988). With the development of Adaptive Optic system (AO), a large amount of work has been done for improving the rejection rate of such coronagraphs. First developments were done with only tip-tilt correction (Walker et al. 1994; Nakajima et al. 1994). The latter coronograph drove to the discovery of Gl 105 C, a star close to the Hydrogen burning limit (Golimowsky et al. 1995) and to the discovery of the first brown dwarf: Gl 229B (Nakajima et al. 1995). More recently, Beuzit et al. (1997) placed a coronagraph behind the COME-ONE-PLUS adaptive optics system (50 actuators) and showed ratio of 105accessible at 2 arcsec. At the beginning of 1999, Lowrance et al. (1999) and Schneider et al. (1999) obtained impressive results on dust disks around young stellar objects using the coronagraph installed with NICMOS on HST. But all coronagraphs cited above were designed on the basis of Lyot coronagraph (1939). In fact a typical layout for a Lyot coronagraph shows a mask in the focal plane that removes the major contribution of the star and a Lyot stop placed in the pupil plane so as to reduce light diffracted by the mask. However, to obtain good extinction with such a coronagraph, even with perfect incoming wavefront, the width of the mask can hardly be less than 6 times the width of the theoretical diffraction pattern (Malbet 1996). This characteristic prevents detection of close companions.

Recently new types of coronagraph has been proposed that show better theoretical extinction than the Lyot coronagraph and which do not prevent imaging as close as the first Airy ring: the Achromatic Interfero Coronagraph (Gay & Rabbia 1996) and the Phase Mask Coronagraph (Roddier & Roddier 1997). Both of them show large reduction of the light of a star for a spaced-based telescope (Rabbia et al. 1997; Rabbia et al. 1998; Roddier & Roddier 1997). Moreover a study of the expected performance of the Achromatic Interfero Coronagraph (AIC) for ground based observation (Paper I: Baudoz et al. 1999) presents such encouraging assessments that it is inviting to carry on observations using a real device. In this perspective we have developed an AIC-prototype in order to confront theoretical estimates and effectives results. The goal of this paper is to present and discuss the results obtained with AIC on a 1.5 m telescope using AO. After a reminding of the principle of AIC and the description of the conditions of observation, first results are analysed. We eventually show the limitations of the AIC device effectively used for these observations and we compare expected performance with obtained results.


  \begin{figure}
\resizebox{8cm}{!}{\includegraphics{ds9360f1.eps}}
\end{figure} Figure 1: Optical sketch of the experiment used for this observation run


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