Imaging Survey for Faint Companions with Shaped Pupil Masks

摘要

A combination of Spergel's innovative gaussian-shaped pupil masks with future space-based and ground-based adaptive optics telescopes will offer great sensitivity for direct imaging of faint companions including brown dwarfs and extra-solar planets around nearby stars. Here we propose a quick way to fully achieve its potential for deep contrast imaging surveys with a great speed in a conventionally designed telescope. In our approach, two Gaussian pupil masks set on each side of the secondary obscuration, slightly penetrating the telescope spider structures, are placed in a cryogenic pupil plane in an infrared (IR) camera to allow the collimated telescope beams to pass through. This simple design will enable ～10~(-6) deep contrast imaging while enjoying diffraction-limited imaging from the full telescope aperture for discovering faint companions closest to the primary. The survey speed with this design will be at least 3-4 times faster than a conventional coronagraph due to its simple alignment. This contrast should allow an image survey for Jupiter-like planets to ～ 20 pc in the thermal IR with next generation large ground-based and space based telescopes. A combination of this shaped pupil mask with an apodizing focal plane mask will enable deeper contrast than the pupil mask alone. However, it takes a much longer time to align the system, so this mode will be used for characterization of faint companion systems from the candidates identified from the survey. A prototype gaussian pupil mask in the Penn State near IR Imager and Spectrograph (PIRIS) has been tested at the Mt. Wilson 100 inch telescope with high order natural guide star adaptive optics (AO) and has demonstrated its tremendous potential. The contrast is about 10~(-3)-10~(-4) beyond 7 λ/D. The contrast is about 5 times better than the direct AO image, and comparable to an IR coronagraph in the same instrument. Recent lab experiments show that 3x10~(-6) at ～ 4 λ/D can be reached with a combination of a Gaussian pupil mask with an apodizing focal plane mask.