Binary-Shaped Pupil Coronagraphs for High-Contrast Imaging Using a Space Telescope with Central Obstructions

We present sets of configurations of binary-shaped pupil coronagraphs optimized for a realistic space telescope to directly detect extrasolar giant planets. For the purpose of mid-infrared observations, the target contrast ratio is set to $10^{-7}$ . We made a systematic assessment of the performance of two recently proposed pupil shapes, “checkerboard” and “concentric ring” masks, where a large central obstruction due to a secondary mirror and its related support spiders was introduced into the telescope pupil. It turned out that, if the secondary mirror diameter is smaller than $\sim 15 \%$ of the diameter of the primary, the checkerboard-type masks are more promising in terms of the total high-contrast area. With such a small secondary, we propose to modify the original symmetrical checkerboard apodization function. This modification enables us to achieve a $10^{-7}$ contrast at an inner working angle (IWA) of $4.0 \,\lambda/D$ . On the other hand, when the secondary mirror size cannot be reduced to that level, the concentric ring masks are preferable because of their larger transmission. It was also found that the transmission through the optimal binary masks exhibits two characteristic features as the IWA increases: firstly, abrupt increases and secondly, plateaus. We attribute this nature of the binary apodization functions to the existence of threshold IWAs that allow large openings in the pupil.