PISCO can be used as a Bernard Lyot's coronagraph by placing adequate masks in the entrance image plane (I1) and in the plane (P1) (cf. Fig. 1). This mode was successfully tested in 1994 with long integrations on a conventional CCD detector. Speckle imaging has little interest in this mode since the mask needs to be quite large (a few times the FWHM seeing) to hide most of the brightness of the central target. This mode would take its real advantage with an adaptive optics bonnette and a small image plane mask, to investigate closer to the target.
A four-hole pupil mask (Fig. 8) can also be used to suppress the diffraction image of the spider of the telescope. This reduces the diffusion of a bright object and allows for the detection of a faint close companion or stellar envelope (Fig. 9).
Figure 8: Pupil mask used to remove the diffraction pattern
of the spider in the coronagraphy mode.
Figure: Profile of a star with
(dashed line) and without (solid line)
the pupil mask of Fig. 8