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Hubble Space Telescope

Each plot is divided into three panels representing the coronagraphic performance for the F435W, F606W, and F814W filters. Each panel has three curves that represent the average surface brightness profiles of the PSFs of three types of stars (A1V, G2V, and M2V) placed behind the occulting spot. The surface brightnesses profiles are shown as a function of angular distance from the center of the occulting spot, and are given in units of electrons/pixel/sec normalized in each case to a Johnson V magnitude of 5. The sky background and dark current are included to the PSFs. With these curves, the user can determine the signal and noise values of the background over most of the field of view simply by scaling the curves according to the desired exposure time and magnitude of the occulted star.

Also plotted in each panel are the peak-pixel (red bars) and 80% encircled energy (blue bars) count rates in electrons/sec for two types of field point sources having Johnson V magnitudes of 20, 22, and 24. The solid bars represent field sources with a flat continuum spectrum, and the dashed bars represent field sources with a very red M6 V spectrum. The relative positions of the bars and the occulted PSF curves give the user a sense of the expected image contrast for faint neutral and red sources as a function of separation from the occulted central star. Again, the user can scale these bars up or down to match their desired exposure time and limiting field magnitude, and then determine from the scaled bars and PSF curves the final S/N ratios of their field source.