A stellar coronograph for the COME-ON-PLUS adaptive optics system .2. First astronomical results

We present here the first scientific results obtained with the coronograph described by Beuzit et al. (1996, hereafter paper I), developed to be used together with the COME-ON-PLUS/ADONIS adaptive optics (AO) system. Two IRAS excess Main Sequence (MS) stars, namely HR 4796 and HR 2020 (beta Pictoris), have been observed. No circumstellar disk is detected around HR 4796, down to 2'' from the star. This new constraint on its circumstellar environment is discussed. The photometry in the J, H, and K bands allows us to derive a G0 to G2 spectral type for a faint companion located at 4.7''. The beta Pictoris disk is detected through scattered light as close as 1.5'' from the star. We derive the radial mid-plane brightness from 1.5'' to 6'', and the FWHM from 2'' to 6''. We compare our results with other observations: here, the disk appears thinner than previously, and its surface brightness radial distribution gets flatter in the inner part. These results are then discussed in terms of density of the circumstellar matter.